Media Control Channel Framework (CFW) Call Flow Examples

This document provides a list of typical MEDIACTRL Media Control Channel Framework call flows. The motivation for this comes from our implementation experience with the framework and its protocol. This drove us to write a simple guide to the use of the several interfaces between Application Servers and MEDIACTRL-based Media Servers, and a base reference document for other implementors and protocol researchers. Following this spirit, this document covers several aspects of the interaction between Application Servers and Media Servers. However, in the context of this document, the call flows almost always depict the interaction between a single Application Server (which, for the sake of conciseness, is called the AS from now on) and a single Media Server (MS). In , some flows involving more entities by means of a Media Resource Broker compliant with are presented. To help readers understand all the flows (as related to both SIP dialogs and Media Control Channel Framework (CFW) transactions), the domains hosting the AS and the MS in all the scenarios are called 'as.example.com' and 'ms.example.net', respectively, per . The flows will often focus more on the CFW interaction, rather than on the other involved protocols, e.g., SIP , the Session Description Protocol (SDP) , or RTP . In the next paragraphs, a brief overview of our implementation approach is described, with particular focus on protocol-related aspects. This involves state diagrams that depict both the client side (the AS) and the server side (the MS). Of course, this section is not at all to be considered a mandatory approach to the implementation of the framework. It is only meant to help readers understand how the framework works from a practical point of view. Once done with these preliminary considerations, in the subsequent sections real-life scenarios are addressed. In this context, first of all, the establishment of the Control Channel is dealt with. After that, some use-case scenarios involving the most typical multimedia applications are depicted and described. It is worth pointing out that this document is not meant in any way to be a self-contained guide to implementing a MEDIACTRL-compliant framework. The specifications are a mandatory read for all implementors, especially because this document follows their guidelines but does not delve into the details of every aspect of the protocol.

Note that due to RFC formatting conventions, SIP/SDP and CFW lines whose content exceeds 72 characters are split across lines. This line folding is marked by a backslash at the end of the first line. This backslash, the preceding whitespace, the following CRLF, and the whitespace beginning the next line would not appear in the actual protocol contents. Note also that the indentation of the XML content is only provided for readability. Actual messages will follow strict XML syntax, which allows, but does not require, indentation. Due to the same limit of 72 characters per line, this document also sometimes splits the content of XML elements across lines. Please be aware that when this happens, no whitespace is actually meant to be at either the beginning or the end of the element content. Note also that a few diagrams show arrows that go from a network entity to itself. It's worth pointing out that such arrows do not represent any transaction message but are rather meant as an indication to the reader that the involved network entity made a decision, within its application logic, according to the input it previously received.

This document uses the same terminology as , , , and . The following terms are only a summarization of the terms most commonly used in this context and are mostly derived from the terminology used in the related documents: connection-oriented media (i.e., TCP and Transport Layer Security (TLS)). Also used to signify the support in SDP for connection-oriented media and the RFCs that define that support ( and ). an entity that requests media processing and manipulation from a Media Server; typical examples are Back-to-Back User Agents (B2BUAs) and endpoints requesting manipulation of a third party's media stream. an entity that performs a service, such as media processing, on behalf of an Application Server; typical provided functions are mixing, announcement, tone detection and generation, and play and record services. a reliable connection between an Application Server and a Media Server that is used to exchange framework messages. runtime control of aspects of an audio playback like speed and volume, via dual-tone multi-frequency (DTMF) signals sent by the user, in a manner that resembles the functions of a VCR (video cassette recorder) controller.

In this document, we embrace an engineering approach to the description of a number of interesting scenarios that can be realized through the careful orchestration of the Media Control Channel Framework entities, namely the Application Server and the Media Server. We will demonstrate, through detailed call flows, how a variegated bouquet of services (ranging from very simple scenarios to much more complicated examples) can be implemented with the functionality currently offered, within the main MEDIACTRL framework, by the Control Packages that have been made available to date. The document aims at being a useful guide for those interested in investigating the inter-operation among MEDIACTRL components, as well as being a base reference document for application developers willing to build advanced services on top of the base infrastructure made available by the framework.

In this section, we present an "informal" view of the main MEDIACTRL protocol interactions, in the form of state diagrams. Each diagram is indeed a classical representation of a Mealy automaton, comprising a number of possible protocol states, indicated with rectangular boxes. Transitions between states are indicated through edges, with each edge labeled with a slash-separated pair representing a specific input together with the associated output (a dash in the output position means that, for that particular input, no output is generated from the automaton). Some of the inputs are associated with MEDIACTRL protocol messages arriving at a MEDIACTRL component while it is in a certain state. This is the case for 'CONTROL', 'REPORT' (in its various "flavors" -- pending, terminate, etc.), '200', '202', and 'Error' (error messages correspond to specific numeric codes). Further inputs represent triggers arriving at the MEDIACTRL automaton from the upper layer, namely the Application Programming Interface used by programmers while implementing MEDIACTRL-enabled services. Such inputs have been indicated with the term 'API' followed by the message that the API itself is triggering (as an example, 'API terminate' is a request to send a 'REPORT' message with a status of 'terminate' to the peering component). Four diagrams are provided. Two of them (Figures and ) describe normal operation of the framework. contains two diagrams describing asynchronous event notifications. embraces the MS perspective, whereas shows the AS side. The upper part of shows how events are generated, on the MS side, by issuing a CONTROL message addressed to the AS; events are acknowledged by the AS through standard 200 responses. Hence, the behavior of the AS, which mirrors that of the MS, is depicted in the lower part of the figure. Coming back to , the diagram shows that the MS activates upon reception of CONTROL messages coming from the AS. The CONTROL messages instruct the MS regarding the execution of a specific command that belongs to one of the available Control Packages. The execution of the received command can either be quick or require some time. In the former case, right after completing its operation, the MS sends back to the AS a 200 message, which basically acknowledges correct termination of the invoked task. In the latter case, the MS first sends back an interlocutory 202 message containing a 'Timeout' value, which lets it enter a different state ('202' sent). While in the new state, the MS keeps on performing the invoked task. If the task does not complete in the provided timeout, the server will update the AS on the other side of the Control Channel by periodically issuing 'REPORT update' messages; each such message has to be acknowledged by the AS (through a '200' response). Eventually, when the MS is done with the required service, it sends to the AS a 'REPORT terminate' message. The transaction is concluded when the AS acknowledges receipt of the message. It is worth pointing out that the MS may send a 202 response after it determines that the request does not contain any errors that cannot be reported in a later REPORT terminate request instead. After the MS sends a 202 response, any error that it (or the API) finds in the request is reported in the final REPORT terminate request. Again, the behavior of the AS, as depicted in , mirrors the above-described actions undertaken at the MS side. The figures also show the cases in which transactions cannot be successfully completed due to abnormal conditions; such conditions always trigger the creation and transmission of a specific 'Error' message that, as mentioned previously, is reported as a numeric error code.

| CONTROL received |---------+ +------------------+ +------------------+ | ^ ^ ^ API 200/200 | | | | | | | | | | | +------------------+ | | | 200/- | API Error/Error | | | +----------------------------+ | | | +-------------+ | | Waiting for | v | last 200 |<------------------------+ +------------+ +-------------+ | | '202' sent | ^ | +------------+ | | | | | +---------------+ | | API terminate/ API terminate/ | | REPORT terminate REPORT terminate | | | +--------------------+ | | 'update' confirmed |------+ API update/ | +--------------------+ | REPORT update | ^ | API update/ | | | REPORT update | | v | | 200/- +---------------+ | +--------------| 'update' sent |<----------------+ +---------------+ ]]>

| CONTROL sent |---------->| 202 received | | +--------------+ +--------------+ | | | | | | | | | | API CONTROL/ | | 200/- | | | send CONTROL | | | | | | | | Error/ | | +------------------+ | | Error | | | Idle/'terminate' |<-+ | | | +------------------+<---------+ | | ^ ^ | | | | REPORT 'terminate'/ | | | | send 200 | | | +--------------------------------+ | REPORT 'update'/ | | send 200 | REPORT 'terminate'/ | | send 200 | | +-----------+ | +---------------------| 'update ' |<--------------+ +-----------+ ^ | | | REPORT 'update'/ +------+ send 200 ]]>

As specified in , the preliminary step to any interaction between an AS and an MS is the establishment of a Control Channel between the two. As explained in the next subsection, this is accomplished by means of a connection-oriented media (COMEDIA) negotiation. This negotiation allows a reliable connection to be created between the AS and the MS. It is here that the AS and the MS agree on the transport-level protocol to use (TCP / Stream Control Transmission Protocol (SCTP)) and whether any application-level security is needed or not (e.g., TLS). For the sake of simplicity, we assume that an unencrypted TCP connection is negotiated between the two involved entities. Once they have connected, a SYNC message sent by the AS to the MS consolidates the Control Channel. An example of how a keep-alive message is triggered is also presented in the following paragraphs. For the sake of completeness, this section also includes a couple of common mistakes that can occur when dealing with the Control Channel establishment.

| | 100 (Trying) | |<------------------------------| | 200 OK (COMEDIA) | |<------------------------------| | ACK | |------------------------------>| | | |==============================>| | TCP CONNECT (CTRL CHANNEL) | |==============================>| | | | SYNC (Dialog-ID, etc.) | |+++++++++++++++++++++++++++++>>| | |--+ | | | Check SYNC | |<-+ | 200 OK | |<<+++++++++++++++++++++++++++++| | | . . . . ]]>

As a first step, the AS and the MS establish a Control SIP dialog. This is usually originated by the AS itself. The AS generates a SIP INVITE message containing in its SDP body information about the TCP connection it wants to establish with the MS. In the provided example (see and the attached call flow), the AS wants to actively open a new TCP connection, which on its side will be bound to port 5757. If the request is fine, the MS answers by communicating to the AS the transport address to connect to in order to establish the TCP connection. In the provided example, the MS will listen on port 7575. Once this negotiation is over, the AS can effectively connect to the MS. The negotiation includes additional attributes. The 'cfw-id' attribute is the most important, since it specifies the Dialog-ID, which in turn will be subsequently referred to by both the AS and the MS as specified in .

| | 2. 100 (Trying) | |<------------------------------| | 3. 200 OK (COMEDIA) | |<------------------------------| | 4. ACK | |------------------------------>| | | |==============================>| | TCP CONNECT (CTRL CHANNEL) | |==============================>| | | . . . . ]]>

MS (SIP INVITE) ------------------------ INVITE sip:MediaServer@ms.example.net:5060 SIP/2.0 Via: SIP/2.0/UDP 203.0.113.1:5060;\ branch=z9hG4bK-d8754z-9b07c8201c3aa510-1---d8754z-;rport=5060 Max-Forwards: 70 Contact: To: From: ;tag=4354ec63 Call-ID: MDk2YTk1MDU3YmVkZjgzYTQwYmJlNjE5NTA4ZDQ1OGY. CSeq: 1 INVITE Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER Content-Type: application/sdp Content-Length: 203 v=0 o=lminiero 2890844526 2890842807 IN IP4 as.example.com s=MediaCtrl c=IN IP4 as.example.com t=0 0 m=application 5757 TCP cfw a=connection:new a=setup:active a=cfw-id:5feb6486792a 2. AS <- MS (SIP 100 Trying) ---------------------------- SIP/2.0 100 Trying Via: SIP/2.0/UDP 203.0.113.1:5060; \ branch=z9hG4bK-d8754z-9b07c8201c3aa510-1---d8754z-;rport=5060 To: ;tag=499a5b74 From: ;tag=4354ec63 Call-ID: MDk2YTk1MDU3YmVkZjgzYTQwYmJlNjE5NTA4ZDQ1OGY. CSeq: 1 INVITE Content-Length: 0 3. AS <- MS (SIP 200 OK) ------------------------ SIP/2.0 200 OK Via: SIP/2.0/UDP 203.0.113.1:5060; \ branch=z9hG4bK-d8754z-9b07c8201c3aa510-1---d8754z-;rport=5060 Contact: To: ;tag=499a5b74 From: ;tag=4354ec63 Call-ID: MDk2YTk1MDU3YmVkZjgzYTQwYmJlNjE5NTA4ZDQ1OGY. CSeq: 1 INVITE Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER Content-Type: application/sdp Content-Length: 199 v=0 o=lminiero 2890844526 2890842808 IN IP4 ms.example.net s=MediaCtrl c=IN IP4 ms.example.net t=0 0 m=application 7575 TCP cfw a=connection:new a=setup:passive a=cfw-id:5feb6486792a 4. AS -> MS (SIP ACK) --------------------- ACK sip:MediaServer@ms.example.net:5060 SIP/2.0 Via: SIP/2.0/UDP 203.0.113.1:5060; \ branch=z9hG4bK-d8754z-22940f5f4589701b-1---d8754z-;rport Max-Forwards: 70 Contact: To: ;tag=499a5b74 From: ;tag=4354ec63 Call-ID: MDk2YTk1MDU3YmVkZjgzYTQwYmJlNjE5NTA4ZDQ1OGY. CSeq: 1 ACK Content-Length: 0 ]]>

Once the AS and the MS have successfully established a TCP connection, an additional step is needed before the Control Channel can be used. In fact, as seen in the previous subsection, the first interaction between the AS and the MS happens by means of a SIP dialog, which in turn allows the creation of the TCP connection. This introduces the need for a proper correlation between the above-mentioned entities (SIP dialog and TCP connection), so that the MS can be sure that the connection came from the AS that requested it. This is accomplished by means of a dedicated framework message called a SYNC message. This SYNC message uses a unique identifier called the Dialog-ID to validate the Control Channel. This identifier, as introduced previously, is meant to be globally unique and as such is properly generated by the caller (the AS in the call flow) and added as an SDP media attribute (cfw-id) to the COMEDIA negotiation in order to make both entities aware of its value:

It also offers an additional negotiation mechanism. In fact, the AS uses the SYNC to not only properly correlate, as explained before, but also negotiate with the MS the Control Packages in which it is interested, as well as agree on a 'Keep-Alive' timer needed by both the AS and the MS so that they will know if problems on the connection occur. In the provided example (see and the related call flow), the AS sends a SYNC with a Dialog-ID constructed as needed (using the 'cfw-id' attribute from the SIP dialog) and requests access to two Control Packages: specifically, the Interactive Voice Response (IVR) package and the Mixer package. The AS also instructs the MS that a 100-second timeout is to be used for keep-alive messages. The MS validates the request by matching the received Dialog-ID with the SIP dialog values, and, assuming that it supports the Control Packages the AS requested access to (and for the sake of this document we assume that it does), it answers with a 200 message. Additionally, the MS provides the AS with a list of other unrequested packages it supports (in this case just a dummy package providing testing functionality).

>| | |--+ | | | Check SYNC | |<-+ | 2. 200 OK | |<<+++++++++++++++++++++++++++++| | | . . . . ]]>

MS (CFW SYNC) ---------------------- CFW 6e5e86f95609 SYNC Dialog-ID: 5feb6486792a Keep-Alive: 100 Packages: msc-ivr/1.0,msc-mixer/1.0 2. AS <- MS (CFW 200) --------------------- CFW 6e5e86f95609 200 Keep-Alive: 100 Packages: msc-ivr/1.0,msc-mixer/1.0 Supported: msc-example-pkg/1.0 ]]> The framework-level transaction identifier is obviously the same in both the request and the response (6e5e86f95609), since the AS needs to be able to match the response to the original request. At this point, the Control Channel is finally established, and it can be used by the AS to request services from the MS.

provides a mechanism for implementing a keep-alive functionality. Such a mechanism is especially useful whenever any NAT or firewall sits in the path between an AS and an MS. In fact, NATs and firewalls may have timeout values for the TCP connections they handle, which means that if no traffic is detected on these connections within a specific time they could be shut down. This could be the case for a Control Channel established between an AS and an MS but not used for some time. For this reason, specifies a dedicated framework message (K-ALIVE) that the AS and MS can use in order to generate traffic on the TCP connection and keep it alive. As discussed in , the timeout value for the keep-alive mechanism is set by the SYNC request. Specifically, in the example, the AS specified a value of 100 seconds. In fact, the timeout value is not actually negotiated between the AS and MS, as it is simply specified by whichever endpoint takes the active role. The 100&nbhy;second value is compliant with how NATs and firewalls are usually implemented, since in most cases the timeout value they use before shutting TCP connections down is around 2 minutes. Such a value has a strong meaning within the context of this mechanism. In fact, it means that the active role (the AS, in this case) has to send a K-ALIVE message before those 100 seconds pass; otherwise, the passive role (the MS) will tear down the connection, treating it like a timeout. suggests a more conservative approach towards handling this timeout value, suggesting that the K-ALIVE message be triggered before 80% of the negotiated time passes (80 seconds, in this case). This is exactly the case presented in .

| | | 1. K-ALIVE | |+++++++++++++++++++++++++++++>>| | |--+ Reset the local | | | 'Keep-Alive' | |<-+ timer | 2. 200 OK | |<<+++++++++++++++++++++++++++++| Reset the +--| | local | | | 'Keep-Alive' +->| | timer | | . . . . ]]> After the Control Channel has been established (COMEDIA+SYNC), both the AS and the MS start local 'Keep-Alive' timers mapped to the negotiated keep-alive timeout value (100 seconds). When about 80 seconds have passed since the start of the timer (80% of 100 seconds), the AS sends a framework-level K-ALIVE message to the MS. The message as seen in the protocol message dump is very lightweight, since it only includes a single line with no additional header. When the MS receives the K-ALIVE message, it resets its local 'Keep-Alive' timer and sends a 200 message back as confirmation. As soon as the AS receives the 200 message, it resets its local 'Keep-Alive' timer as well, and the mechanism starts over again. The actual transaction steps are presented below.

MS (K-ALIVE) --------------------- CFW 518ba6047880 K-ALIVE 2. AS <- MS (CFW 200) --------------------- CFW 518ba6047880 200 ]]> If the timer expired in either the AS or the MS (i.e., the K-ALIVE or the 200 arrived after the 100 seconds), the connection and the associated SIP control dialog would be torn down by the entity detecting the timeout, thus ending the interaction between the AS and the MS.

This section will briefly address some types of behavior that could represent the most common mistakes when dealing with the establishment of a Control Channel between an AS and an MS. These scenarios are obviously of interest, since they result in the AS and the MS being unable to interact with each other. Specifically, these simple scenarios will be described: an AS providing the MS with a wrong Dialog-ID in the initial SYNC. an AS sending a generic CONTROL message instead of SYNC as a first transaction. The first scenario is depicted in .

>| | |--+ | | | Check SYNC (wrong!) | |<-+ | 2. 481 | |<<+++++++++++++++++++++++++++++| | | |<-XX- CLOSE TCP CONNECTION -XX-| | | | SIP BYE | |------------------------------>| | | . . . . ]]> This scenario is similar to the scenario presented in , but with a difference: instead of using the correct, expected Dialog-ID in the SYNC message (5feb6486792a, the one negotiated via COMEDIA), the AS uses a wrong value (4hrn7490012c). This causes the SYNC transaction to fail. First of all, the MS sends a framework-level 481 message. This response, when given in reply to a SYNC message, means that the SIP dialog associated with the provided Dialog-ID (the wrong identifier) does not exist. The Control Channel must be torn down as a consequence, and so the MS also closes the TCP connection it received the SYNC message from. The AS at this point is supposed to tear down its SIP control dialog as well, and so it sends a SIP BYE to the MS. The actual transaction is presented below.

MS (CFW SYNC with wrong Dialog-ID) ------------------------------------------- CFW 2b4dd8724f27 SYNC Dialog-ID: 4hrn7490012c Keep-Alive: 100 Packages: msc-ivr/1.0,msc-mixer/1.0 2. AS <- MS (CFW 481) --------------------- CFW 2b4dd8724f27 481 ]]> The second scenario is depicted in .

>| | |--+ First transaction | | | is not a SYNC | |<-+ | 2. 403 | |<<+++++++++++++++++++++++++++++| | | |<-XX- CLOSE TCP CONNECTION -XX-| | | | SIP BYE | |------------------------------>| | | . . . . ]]> This scenario demonstrates another common mistake that could occur when trying to set up a Control Channel. In fact, mandates that the first transaction after the COMEDIA negotiation be a SYNC to conclude the setup. If the AS, instead of triggering a SYNC message as expected, sends a different message to the MS (in the example below, it tries to send an <audit> message addressed to the IVR Control Package), the MS treats it like an error. As a consequence, the MS replies with a framework-level 403 message (Forbidden) and, just as before, closes the TCP connection and waits for the related SIP control dialog to be torn down. The actual transaction is presented below.

MS (CFW CONTROL instead of SYNC) ----------------------------------------- CFW 101fbbd62c35 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 78 2. AS <- MS (CFW 403 Forbidden) ------------------------------- CFW 101fbbd62c35 403 ]]>

The following scenarios have been chosen for their common presence in many rich real-time multimedia applications. Each scenario is depicted as a set of call flows involving both the SIP/SDP signaling (UACs<->AS<->MS) and the Control Channel communication (AS<->MS). All the examples assume that a Control Channel has already been correctly established and SYNCed between the reference AS and MS. Also, unless stated otherwise, the same User Agent Client (UAC) session is referenced in all the examples that will be presented in this document. The UAC session is assumed to have been created as described in :

| | | 180 (Ringing) | | |<------------------| | | |--+ | | | | Handle app(X) | | |<-+ | | | INVITE (Y) as 3PCC | | |-------------------------->| | | 100 (Trying) | | |<--------------------------| | | |--+ Negotiate media | | | | with UAC; map | | |<-+ tags and labels | | 200 OK | | |<--------------------------| | 200 OK | | |<------------------| | | ACK | | |------------------>| | | | ACK | | |-------------------------->| | | | |<<###########################################>>| | RTP Media Stream(s) flowing | |<<###########################################>>| | | | . . . . . . ]]> Note well: This is only an example of a possible approach involving a Third-Party Call Control (3PCC) negotiation among the UAC, the AS, and the MS, and as such is not at all to be considered the mandatory way, nor best common practice, in the presented scenario. provides several different solutions and many details about how 3PCC can be realized, with pros and cons. It is also worth pointing out that the two INVITEs displayed in the figure are different SIP dialogs. The UAC first places a call to a SIP URI for which the AS is responsible. The specific URI is not relevant to the examples, since the application logic behind the mapping between a URI and the service it provides is a matter that is important only to the AS. So, a generic 'sip:mediactrlDemo@as.example.com' is used in all the examples, whereas the service this URI is associated with in the AS logic is mapped scenario by scenario to the case under examination. The UAC INVITE is treated as envisaged in . The INVITE is forwarded by the AS to the MS via a third party (e.g., the 3PCC approach), without the SDP provided by the UAC being touched, in order to have the session fully negotiated by the MS according to its description. The MS matches the UAC's offer with its own capabilities and provides its answer in a 200 OK. This answer is then forwarded, again without the SDP contents being touched, by the AS to the target UAC. This way, while the SIP signaling from the UAC is terminated in the AS, all the media would start flowing directly between the UAC and the MS. As a consequence of this negotiation, one or more media connections are created between the MS and the UAC. They are then addressed, when needed, by the AS and the MS by means of the concatenation of tags, as specified in . How the identifiers are created and addressed is explained by using the sample signaling provided in the following lines.

AS (SIP INVITE) ------------------------- INVITE sip:mediactrlDemo@as.example.com SIP/2.0 Via: SIP/2.0/UDP 203.0.113.2:5063;rport;branch=z9hG4bK1396873708 From: ;tag=1153573888 To: Call-ID: 1355333098 CSeq: 20 INVITE Contact: Content-Type: application/sdp Max-Forwards: 70 User-Agent: Linphone/2.1.1 (eXosip2/3.0.3) Subject: Phone call Expires: 120 Content-Length: 330 v=0 o=lminiero 123456 654321 IN IP4 203.0.113.2 s=A conversation c=IN IP4 203.0.113.2 t=0 0 m=audio 7078 RTP/AVP 0 3 8 101 a=rtpmap:0 PCMU/8000/1 a=rtpmap:3 GSM/8000/1 a=rtpmap:8 PCMA/8000/1 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-11 m=video 9078 RTP/AVP 98 a=rtpmap:98 H263-1998/90000 a=fmtp:98 CIF=1;QCIF=1 2. UAC <- AS (SIP 180 Ringing) ------------------------------ SIP/2.0 180 Ringing Via: SIP/2.0/UDP 203.0.113.2:5063;rport=5063; \ branch=z9hG4bK1396873708 Contact: To: ;tag=bcd47c32 From: ;tag=1153573888 Call-ID: 1355333098 CSeq: 20 INVITE Content-Length: 0 3. AS -> MS (SIP INVITE) ------------------------ INVITE sip:MediaServer@ms.example.net:5060;transport=UDP SIP/2.0 Via: SIP/2.0/UDP 203.0.113.1:5060; \ branch=z9hG4bK-d8754z-8723e421ebc45f6b-1---d8754z-;rport Max-Forwards: 70 Contact: To: From: ;tag=10514b7f Call-ID: NzI0ZjQ0ZTBlMTEzMGU1ZjVhMjk5NTliMmJmZjE0NDQ. CSeq: 1 INVITE Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER Content-Type: application/sdp Content-Length: 330 v=0 o=lminiero 123456 654321 IN IP4 203.0.113.2 s=A conversation c=IN IP4 203.0.113.2 t=0 0 m=audio 7078 RTP/AVP 0 3 8 101 a=rtpmap:0 PCMU/8000/1 a=rtpmap:3 GSM/8000/1 a=rtpmap:8 PCMA/8000/1 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-11 m=video 9078 RTP/AVP 98 a=rtpmap:98 H263-1998/90000 a=fmtp:98 CIF=1;QCIF=1 4. AS <- MS (SIP 100 Trying) ---------------------------- SIP/2.0 100 Trying Via: SIP/2.0/UDP 203.0.113.1:5060; \ branch=z9hG4bK-d8754z-8723e421ebc45f6b-1---d8754z-;rport=5060 To: ;tag=6a900179 From: ;tag=10514b7f Call-ID: NzI0ZjQ0ZTBlMTEzMGU1ZjVhMjk5NTliMmJmZjE0NDQ. CSeq: 1 INVITE Content-Length: 0 5. AS <- MS (SIP 200 OK) ------------------------ SIP/2.0 200 OK Via: SIP/2.0/UDP 203.0.113.1:5060; \ branch=z9hG4bK-d8754z-8723e421ebc45f6b-1---d8754z-;rport=5060 Contact: To: ;tag=6a900179 From: ;tag=10514b7f Call-ID: NzI0ZjQ0ZTBlMTEzMGU1ZjVhMjk5NTliMmJmZjE0NDQ. CSeq: 1 INVITE Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER Content-Type: application/sdp Content-Length: 374 v=0 o=lminiero 123456 654322 IN IP4 ms.example.net s=MediaCtrl c=IN IP4 ms.example.net t=0 0 m=audio 63442 RTP/AVP 0 3 8 101 a=rtpmap:0 PCMU/8000 a=rtpmap:3 GSM/8000 a=rtpmap:8 PCMA/8000 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-15 a=ptime:20 a=label:7eda834 m=video 33468 RTP/AVP 98 a=rtpmap:98 H263-1998/90000 a=fmtp:98 CIF=2 a=label:0132ca2 6. UAC <- AS (SIP 200 OK) ------------------------- SIP/2.0 200 OK Via: SIP/2.0/UDP 203.0.113.2:5063;rport=5063; \ branch=z9hG4bK1396873708 Contact: To: ;tag=bcd47c32 From: ;tag=1153573888 Call-ID: 1355333098 CSeq: 20 INVITE Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER Content-Type: application/sdp Content-Length: 374 v=0 o=lminiero 123456 654322 IN IP4 ms.example.net s=MediaCtrl c=IN IP4 ms.example.net t=0 0 m=audio 63442 RTP/AVP 0 3 8 101 a=rtpmap:0 PCMU/8000 a=rtpmap:3 GSM/8000 a=rtpmap:8 PCMA/8000 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-15 a=ptime:20 a=label:7eda834 m=video 33468 RTP/AVP 98 a=rtpmap:98 H263-1998/90000 a=fmtp:98 CIF=2 a=label:0132ca2 7. UAC -> AS (SIP ACK) ---------------------- ACK sip:mediactrlDemo@as.example.com SIP/2.0 Via: SIP/2.0/UDP 203.0.113.2:5063;rport;branch=z9hG4bK1113338059 From: ;tag=1153573888 To: ;tag=bcd47c32 Call-ID: 1355333098 CSeq: 20 ACK Contact: Max-Forwards: 70 User-Agent: Linphone/2.1.1 (eXosip2/3.0.3) Content-Length: 0 8. AS -> MS (SIP ACK) --------------------- ACK sip:MediaServer@ms.example.net:5060;transport=UDP SIP/2.0 Via: SIP/2.0/UDP 203.0.113.1:5060; \ branch=z9hG4bK-d8754z-5246003419ccd662-1---d8754z-;rport Max-Forwards: 70 Contact: To: ;tag=10514b7f Call-ID: NzI0ZjQ0ZTBlMTEzMGU1ZjVhMjk5NTliMmJmZjE0NDQ. CSeq: 1 ACK Content-Length: 0 ]]> As a result of the 3PCC negotiation just presented, the following relevant information is retrieved: The 'From' and 'To' tags (10514b7f and 6a900179, respectively) of the AS<->MS session:

;tag=10514b7f ^^^^^^^^ To: ;tag=6a900179 ^^^^^^^^ ]]> The labels associated with the negotiated media connections, in this case an audio stream (7eda834) and a video stream (0132ca2):

These four identifiers allow the AS and MS to univocally and unambiguously address to each other the connections associated with the related UAC. Specifically: 10514b7f:6a900179, the concatenation of the 'From' and 'To' tags through a colon (':') token, addresses all the media connections between the MS and the UAC. 10514b7f:6a900179 <-> 7eda834, the association of the previous value with the label attribute, addresses only one of the media connections of the UAC session (in this case, the audio stream). Since, as will be made clearer in the example scenarios, the explicit identifiers in requests can only address 'from:tag' connections, an additional mechanism will be required to have a finer control of individual media streams (i.e., by means of the <stream> element in package-level requests). The mapping that the AS makes between the UACs<->AS and the AS<->MS SIP dialogs is out of scope for this document. We just assume that the AS knows how to address the right connection according to the related session it has with a UAC (e.g., to play an announcement to a specific UAC). This is obviously very important, since the AS is responsible for all the business logic of the multimedia application it provides.

The echo test is the simplest example scenario that can be achieved by means of an MS. It basically consists of a UAC directly or indirectly "talking" to itself. A media perspective of such a scenario is depicted in .

| Media | | A |<=========================| Server | +-------+ A (RTP) +--------+ ]]> From the framework point of view, when the UAC's leg is not attached to anything yet, what appears is shown in : since there's no connection involving the UAC yet, the frames it might be sending are discarded, and nothing is sent to it (except for silence, if its transmission is requested).

>-------x | o.....<<.......x | | | +------+ ]]> Starting from these considerations, two different approaches to the Echo Test scenario are explored in this document: a Direct Echo Test approach, where the UAC directly talks to itself. a Recording-based Echo Test approach, where the UAC indirectly talks to itself.

In the Direct Echo Test approach, the UAC is directly connected to itself. This means that, as depicted in , each frame the MS receives from the UAC is sent back to it in real time.

>-------@ | o-----<<-------@ | | | +------+ ]]> In the framework, this can be achieved by means of the Mixer Control Package , which is in charge of joining connections and conferences. A sequence diagram of a potential transaction is depicted in :

>| | | |--+ self- | | | | join | | 2. 200 OK |<-+ UAC | |<<++++++++++++++++++++++++++++++++| | | | |<<######################################################>>| | Everything is now echoed back to the UAC | |<<######################################################>>| | | | . . . . . . ]]> The transaction steps have been numbered and are explained below: The AS requests the joining of the connection to itself by sending to the MS a CONTROL request (1) that is specifically meant for the conferencing Control Package (msc-mixer/1.0). A <join> request is used for this purpose, and since the connection must be attached to itself, both id1 and id2 attributes are set to the same value, i.e., the connectionid. The MS, having checked the validity of the request, enforces the joining of the connection to itself. This means that all the frames sent by the UAC are sent back to it. To report the result of the operation, the MS sends a 200 OK (2) in reply to the AS, thus ending the transaction. The transaction ended successfully, as indicated by the body of the message (the 200 status code in the <response> tag). The complete transaction -- that is, the full bodies of the exchanged messages -- is provided in the following lines:

MS (CFW CONTROL) ------------------------- CFW 4fed9bf147e2 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 130 2. AS <- MS (CFW 200 OK) ------------------------ CFW 4fed9bf147e2 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 ]]>

In the Recording-based Echo Test approach, the UAC is NOT directly connected to itself, but rather indirectly. This means that, as depicted in , each frame the MS receives from the UAC is first recorded; then, when the recording process is ended, the whole recorded frames are played back to the UAC as an announcement.

>-------+~~~~~> (recording.wav) ~~+ o-----<<-------+ | | | ^ | v +--|---+ | +~~~~~~~~~~~<<~~~~~~~~~~~~+ ]]> In the framework, this can be achieved by means of the IVR Control Package , which is in charge of both the recording and the playout phases. However, the whole scenario cannot be accomplished in a single transaction; at least two steps, in fact, need to be performed: First, a recording (preceded by an announcement, if requested) must take place. Then, a playout of the previously recorded media must occur. This means that two separate transactions need to be invoked. A sequence diagram of a potential multiple transaction is depicted in :

>| | | A2. 202 | | |<<++++++++++++++++++++++++++++++++| prepare & | | |--+ start | | | | the | | A3. REPORT (terminate) |<-+ dialog | |<<++++++++++++++++++++++++++++++++| | | A4. 200 OK | | |++++++++++++++++++++++++++++++++>>| | | | |<<########################################################| | "This is an echo test: say something" | |<<########################################################| | | | |########################################################>>| | 10 s of audio from the UAC are recorded |--+ save |########################################################>>| | in a | | |<-+ file | | B1. CONTROL () | | |<<++++++++++++++++++++++++++++++++| | Use recorded +--| B2. 200 OK | | file to play | |++++++++++++++++++++++++++++++++>>| | announcement +->| | | | C1. CONTROL (play recorded) | | |++++++++++++++++++++++++++++++++>>| | | C2. 202 | | |<<++++++++++++++++++++++++++++++++| prepare & | | |--+ start | | | | the | | C3. REPORT (terminate) |<-+ dialog | |<<++++++++++++++++++++++++++++++++| | | C4. 200 OK | | |++++++++++++++++++++++++++++++++>>| | | | |<<########################################################| | "Can you hear me? It's me, UAC, talking" | |<<########################################################| | | | | | D1. CONTROL () | | |<<++++++++++++++++++++++++++++++++| | | D2. 200 OK | | |++++++++++++++++++++++++++++++++>>| | | | . . . . . . ]]> The first obvious difference that stands out when looking at the diagram is that, unlike the Direct Echo scenario, the MS does not reply with a 200 message to the CONTROL request originated by the AS. Instead, a 202 provisional message is sent first, followed by a REPORT message. The 202+REPORT(s) mechanism is used whenever the MS wants to tell the AS that the requested operation might take more time than the limit specified in the definition of the Control Package. So, while the <join> operation in the Direct Echo scenario was expected to be fulfilled in a very short time, the IVR request was assumed to last longer. A 202 message provides a timeout value and tells the AS to wait a bit, since the preparation of the dialog might not happen immediately. In this example, the preparation ends before the timeout, and so the transaction is concluded with a 'REPORT terminate', which reports the end of the transaction (as did the 200 message in the previous example). If the preparation took longer than the timeout, an additional 'REPORT update' would have been sent with a new timeout value, and so on, until completion by means of a 'REPORT terminate'. Note that the REPORT mechanism depicted is only shown to clarify its behavior. In fact, the 202+REPORT mechanism is assumed to be involved only when the requested transaction is expected to take a long time (e.g., retrieving a large media file for a prompt from an external server). In this scenario, the transaction would be prepared in much less time and as a consequence would very likely be completed within the context of a simple CONTROL+200 request/response. The following scenarios will only involve 202+REPORTs when they are strictly necessary. Regarding the dialog itself, note how the AS-originated CONTROL transactions are terminated as soon as the requested dialogs start. As specified in , the MS uses a framework CONTROL message to report the result of the dialog and how it has proceeded. The two transactions (the AS-generated CONTROL request and the MS-generated CONTROL event) are correlated by means of the associated dialog identifier, as explained below. As before, the transaction steps have been numbered. The two transactions are distinguished by the preceding letter (A,B=recording, C,D=playout). The AS, as a first transaction, invokes a recording on the UAC connection by means of a CONTROL request (A1). The body is for the IVR package (msc-ivr/1.0) and requests the start (<dialogstart>) of a new recording context (<record>). The recording must be preceded by an announcement (<prompt>), must not last longer than 10 s (maxtime), and cannot be interrupted by a DTMF tone (dtmfterm=false). This is only done once (the missing repeatCount attribute is 1 by default for a <dialog>), which means that if the recording does not succeed the first time, the transaction must fail. A video recording is requested (considering that the associated connection includes both audio and video and no restriction is enforced on streams to record), which is to be fed by both of the negotiated media streams. A beep has to be played (beep=true) right before the recording starts, to notify the UAC. As seen before, the MS sends a provisional 202 response to let the AS know that the operation might need some time. In the meantime, the MS prepares the dialog (e.g., by retrieving the announcement file, for which an HTTP URL is provided, and by checking that the request is well formed) and if all is fine it starts it, notifying the AS with a new REPORT (A3) with a terminated status. As explained previously, interlocutory REPORT messages with an update status would have been sent if the preparation took longer than the timeout provided in the 202 message (e.g., if retrieving the resource via HTTP took longer than expected). Once the dialog has been prepared and started, the UAC connection is then passed to the IVR package, which first plays the announcement on the connection, followed by a beep, and then records all the incoming frames to a buffer. The MS also provides the AS with a unique dialog identifier (dialogid) that will be used in all subsequent event notifications concerning the dialog it refers to. The AS acks the latest REPORT (A4), thus terminating this transaction, and waits for the results. Once the recording is over, the MS prepares a notification CONTROL (B1). The <event> body is prepared with an explicit reference to the previously provided dialog identifier, in order to make the AS aware of the fact that the notification is related to that specific dialog. The event body is then completed with the recording-related information (<recordinfo>), in this case the path to the recorded file (here, an HTTP URL) that can be used by the AS for anything it needs. The payload also contains information about the prompt (<promptinfo>), which is, however, not relevant to the scenario. The AS concludes this first recording transaction by acking the CONTROL event (B2). Now that the first transaction has ended, the AS has the 10&nbhy;s recording of the UAC talking and can let the UAC hear it by having the MS play it for the UAC as an announcement: In the second transaction, the AS invokes a playout on the UAC connection by means of a new CONTROL request (C1). The body is once again for the IVR package (msc-ivr/1.0), but this time it requests the start (<dialogstart>) of a new announcement context (<prompt>). The file to be played is the file that was recorded before (<media>). Again, the usual provisional 202 (C2) takes place. In the meantime, the MS prepares and starts the new dialog, and notifies the AS with a new REPORT (C3) with a terminated status. The connection is then passed to the IVR package, which plays the file on it. The AS acks the terminating REPORT (C4), now waiting for the announcement to end. Once the playout is over, the MS sends a CONTROL event (D1) that contains in its body (<promptinfo>) information about the just-concluded announcement. As before, the proper dialogid is used as a reference to the correct dialog. The AS concludes this second and last transaction by acking the CONTROL event (D2). As in the previous paragraph, the whole CFW interaction is provided for a more in-depth evaluation of the protocol interaction.

MS (CFW CONTROL, record) ---------------------------------- CFW 796d83aa1ce4 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 265 A2. AS <- MS (CFW 202) ---------------------- CFW 796d83aa1ce4 202 Timeout: 5 A3. AS <- MS (CFW REPORT terminate) ----------------------------------- CFW 796d83aa1ce4 REPORT Seq: 1 Status: terminate Timeout: 25 Content-Type: application/msc-ivr+xml Content-Length: 137 A4. AS -> MS (CFW 200, ACK to 'REPORT terminate') ------------------------------------------------- CFW 796d83aa1ce4 200 Seq: 1 B1. AS <- MS (CFW CONTROL event) -------------------------------- CFW 0eb1678c0bfc CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 403 B2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 0eb1678c0bfc 200 C1. AS -> MS (CFW CONTROL, play) -------------------------------- CFW 1632eead7e3b CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 241 C2. AS <- MS (CFW 202) ---------------------- CFW 1632eead7e3b 202 Timeout: 5 C3. AS <- MS (CFW REPORT terminate) ----------------------------------- CFW 1632eead7e3b REPORT Seq: 1 Status: terminate Timeout: 25 Content-Type: application/msc-ivr+xml Content-Length: 137 C4. AS -> MS (CFW 200, ACK to 'REPORT terminate') ------------------------------------------------- CFW 1632eead7e3b 200 Seq: 1 D1. AS <- MS (CFW CONTROL event) -------------------------------- CFW 502a5fd83db8 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 230 D2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 502a5fd83db8 200 ]]>

Another scenario that might involve the interaction between an AS and an MS is the classic phone call between two UACs. In fact, even though the most straightforward way to achieve this would be to let the UACs negotiate the session and the media to be used between them, there are cases when the services provided by an MS might also prove useful for such phone calls. One of these cases is when the two UACs have no common supported codecs: having the two UACs directly negotiate the session would result in a session with no available media. Involving the MS as a transcoder would in this case still allow the two UACs to communicate. Another interesting case is when the AS (or any other entity on whose behalf the AS is working) is interested in manipulating or monitoring the media session between the UACs, e.g., to record the conversation. A similar scenario will be dealt with in . Before looking at how such a scenario might be accomplished by means of the Media Control Channel Framework, it is worth mentioning what the SIP signaling involving all the interested parties might look like. In fact, in such a scenario, a 3PCC approach is absolutely needed. An example is provided in . Again, the presented example is not at all to be considered best common practice when 3PCC is needed in a MEDIACTRL-based framework. It is only described in order to help the reader more easily understand what the requirements are on the MS side, and as a consequence what information might be required. provides a much more detailed overview on 3PCC patterns in several use cases. Only an explanatory sequence diagram is provided, without delving into the details of the exchanged SIP messages.

| | | | 100 Trying | | | | Call-Id: A | | |<----------------------------------| | | | INVITE (no offer) | | | | Call-Id: B | | | |<--------------------| | | | 180 Ringing | | | | Call-Id: B | | | |-------------------->| | | | 180 Ringing | | | | Call-Id: A | | |<----------------------------------| | | | | INVITE (offer A) | | | | Call-Id: C | | | |-------------------------->| | | | 200 OK (offer A') | | | | Call-Id: C | | | |<--------------------------| | | | ACK | | | | Call-Id: C | | | |-------------------------->| | | 200 OK (offer B) | | | | Call-Id: B | | | |-------------------->| | | | | INVITE (offer B) | | | | Call-Id: D | | | |-------------------------->| | | | 200 OK (offer B') | | | | Call-Id: D | | | |<--------------------------| | | | ACK | | | | Call-Id: D | | | |-------------------------->| | | ACK (offer B') | | | | Call-Id: B | | | |<--------------------| | | | 200 OK (offer A') | | | | Call-Id: A | | |<----------------------------------| | | ACK | | | | Call-Id: A | | | |---------------------------------->| | | | | | . . . . . . . . ]]> In this example, UAC1 wants to place a phone call to UAC2. To do so, it sends an INVITE to the AS with its offer A. The AS sends an offerless INVITE to UAC2. When UAC2 responds with a 180, the same message is forwarded by the AS to UAC1 to notify it that the callee is ringing. In the meantime, the AS also adds a leg to the MS for UAC1, as explained at the beginning of . To do so, it of course uses the offer A that UAC1 made. Once UAC2 accepts the call by providing its own offer B in the 200, the AS also adds a leg for offer B to the MS. At this point, the negotiation can be completed by providing the two UACs with the SDP answer negotiated by the MS with them (A' and B', respectively). Of course, this is only one way to deal with the signaling and shall not be considered an absolutely mandatory approach. Once the negotiation is over, the two UACs are not in communication yet. In fact, it's up to the AS now to actively trigger the MS to somehow attach their media streams to each other, by referring to the connection identifiers associated with the UACs as explained previously. This document presents two different approaches that might be followed, according to what needs to be accomplished. A generic media perspective of the phone call scenario is depicted in . The MS is basically in the media path between the two UACs.

| Media |===================>| UAC | | 1 |<===================| Server |<===================| 2 | +-------+ UAC2 (RTP) +--------+ UAC2 (RTP) +-------+ ]]> From the framework point of view, when the UACs' legs are not attached to anything yet, what appears is shown in : since there are no connections involving the UACs yet, the frames they might be sending are discarded, and nothing is sent to them (except for silence, if its transmission is requested).

>-------x x.......>>.....o o.....<<.......x x-------<<-----o | | +--------------+ ]]>

The Direct Connection approach is the easiest, and a more straightforward, approach to get the phone call between the two UACs to work. The idea is basically the same as that of the Direct Echo approach. A <join> directive is used to directly attach one UAC to the other, by exploiting the MS to only deal with the transcoding/adaption of the flowing frames, if needed. This approach is depicted in .

>-------+~~~>>~~~+------->>-----o o-----<<-------+~~~<<~~~+-------<<-----o | | +--------------+ ]]>

>| | | | |--+ join | | | | | UAC1 | | | 2. 200 OK |<-+ UAC2 | | |<<++++++++++++++++++++++++++++++++++| | | | | |<<#######################################################>>| | UAC1 can hear UAC2 talking | |<<#######################################################>>| | | | | | |<<###########################################>>| | | UAC2 can hear UAC1 talking | | |<<###########################################>>| | | | | |<*talking*>| | | . . . . . . . . ]]> The framework transactions needed to accomplish this scenario are very trivial and easy to understand. They are basically the same as those presented in the Direct Echo Test scenario; the only difference is in the provided identifiers. In fact, this time the MS is not supposed to attach the UACs' media connections to themselves but has to join the media connections of two different UACs, i.e., UAC1 and UAC2. This means that in this transaction, id1 and i2 will have to address the media connections of UAC1 and UAC2. In the case of a successful transaction, the MS takes care of forwarding all media coming from UAC1 to UAC2 and vice versa, transparently taking care of any required transcoding steps, if necessary.

MS (CFW CONTROL) ------------------------- CFW 0600855d24c8 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 130 2. AS <- MS (CFW 200 OK) ------------------------ CFW 0600855d24c8 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 ]]> Such a simple approach has its drawbacks. For instance, with such an approach, recording a conversation between two users might be tricky to accomplish. In fact, since no mixing would be involved, only the single connections (UAC1<->MS and UAC2<->MS) could be recorded. If the AS wants a conversation-recording service to be provided anyway, it needs additional business logic on its side. An example of such a use case is provided in .

The approach described in surely works for a basic phone call but, as explained previously, might have some drawbacks whenever more advanced features are needed. For instance, one can't record the whole conversation -- only the single connections -- since no mixing is involved. Additionally, even the single task of playing an announcement over the conversation could be complex, especially if the MS does not support implicit mixing over media connections. For this reason, in more advanced cases a different approach might be taken, like the conference-based approach described in this section. The idea is to use a mixing entity in the MS that acts as a bridge between the two UACs. The presence of this entity allows more customization of what needs to be done with the conversation, like the recording of the conversation that has been provided as an example. The approach is depicted in . The mixing functionality in the MS will be described in more detail in the following section (which deals with many conference-related scenarios), so only some hints will be provided here for basic comprehension of the approach.

>-------+~~>{#}::>+:::::::>>:::::o o:::::<<:::::::+<::{#}<~~+-------<<-----o | : | | : | +-------:-------+ : +::::> (conversation.wav) ]]> To identify a single sample scenario, let's consider a phone call that the AS wants to record. shows how this could be accomplished in the Media Control Channel Framework. This example, as usual, hides the previous interaction between the UACs and the AS and instead focuses on the Control Channel operations and what follows.

>| | | | |--+ create | | | | | conf and | | | A2. 200 OK (conferenceid=Y) |<-+ its ID | | |<<++++++++++++++++++++++++++++++++| | | | | | | | B1. CONTROL (record for 10800 s) | | | |++++++++++++++++++++++++++++++++>>| | | | |--+ start | | | | | the | | | B2. 200 OK |<-+ dialog | | |<<++++++++++++++++++++++++++++++++| | Recording +--| | | of the mix | | | | has started +->| | | | | C1. CONTROL (join UAC1<->confY) | | | |++++++++++++++++++++++++++++++++>>| | | | |--+ join | | | | | UAC1 & | | | C2. 200 OK |<-+ confY | | |<<++++++++++++++++++++++++++++++++| | | | | |<<####################################################>>| | Now UAC1 is mixed in the conference | |<<####################################################>>| | | | | | | | D1. CONTROL (join UAC2<->confY) | | | |++++++++++++++++++++++++++++++++>>| | | | |--+ join | | | | | UAC2 & | | | D2. 200 OK |<-+ confY | | |<<++++++++++++++++++++++++++++++++| | | | | | |<<########################################>>| | | Now UAC2 is mixed too | | |<#########################################>>| | | | | |<*talking*>| | | | | | | . . . . . . . . ]]> The AS uses two different packages to accomplish this scenario: the Mixer package (to create the mixing entity and join the UACs) and the IVR package (to record what happens in the conference). The framework transaction steps can be described as follows: First of all, the AS creates a new hidden conference by means of a <createconference> request (A1). This conference is properly configured according to the use it is assigned to. In fact, since only two participants will be joined to it, both 'reserved&nbhy;talkers' and 'reserved-listeners' are set to 2, just as the 'n' value for the N-best audio mixing algorithm. The video layout is also set accordingly (<single-view>/<dual-view>). The MS sends notification of the successful creation of the new conference in a 200 framework message (A2). The identifier assigned to the conference, which will be used in subsequent requests addressed to it, is 6013f1e. The AS requests a new recording for the newly created conference. To do so, it places a proper request to the IVR package (B1). The AS is interested in a video recording (type=video/mpeg), which must not last longer than 3 hours (maxtime=10800s), after which the recording must end. Additionally, no beep must be played on the conference (beep=false), and the recording must start immediately whether or not any audio activity has been reported (vadinitial=false is the default value for <record>). The transaction is handled by the MS, and when the dialog has been successfully started, a 200 OK is issued to the AS (B2). The message contains the dialogid associated with the dialog (00b29fb), which the AS must refer to for later notifications. At this point, the AS attaches both UACs to the conference with two separate <join> directives (C1/D1). When the MS confirms the success of both operations (C2/D2), the two UACs are actually in contact with each other (even though indirectly, since a hidden conference they're unaware of is on their path), and their media contribution is recorded.

MS (CFW CONTROL, createconference) -------------------------------------------- CFW 238e1f2946e8 CONTROL Control-Package: msc-mixer Content-Type: application/msc-mixer+xml Content-Length: 395

A2. AS <- MS (CFW 200 OK) ------------------------- CFW 238e1f2946e8 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 151 B1. AS -> MS (CFW CONTROL, record) ---------------------------------- CFW 515f007c5bd0 CONTROL Control-Package: msc-ivr Content-Type: application/msc-ivr+xml Content-Length: 226 B2. AS <- MS (CFW 200 OK) ------------------------- CFW 515f007c5bd0 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 137 C1. AS -> MS (CFW CONTROL, join) -------------------------------- CFW 0216231b1f16 CONTROL Control-Package: msc-mixer Content-Type: application/msc-mixer+xml Content-Length: 123 C2. AS <- MS (CFW 200 OK) ------------------------- CFW 0216231b1f16 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 D1. AS -> MS (CFW CONTROL, join) -------------------------------- CFW 140e0f763352 CONTROL Control-Package: msc-mixer Content-Type: application/msc-mixer+xml Content-Length: 124 D2. AS <- MS (CFW 200 OK) ------------------------- CFW 140e0f763352 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 ]]> The recording of the conversation can subsequently be accessed by the AS by waiting for an event notification from the MS. This event, which will be associated with the previously started recording dialog, will contain the URI of the recorded file. Such an event may be triggered by either a natural completion of the dialog (e.g., the dialog has reached its programmed 3 hours) or any interruption of the dialog itself (e.g., the AS actively requests that the recording be interrupted, since the call between the UACs ended).

The previous section described how to take advantage of the conferencing functionality of the Mixer package in order to allow the recording of phone calls in a simple way. However, using a dedicated mixer just for a phone call might be considered overkill. This section shows how recording a conversation and subsequently playing it out can be accomplished without a mixing entity involved in the call, i.e., by using the Direct Connection approach as described in . As explained previously, if the AS wants to record a phone call between two UACs, the use of just the <join> directive without a mixer forces the AS to just rely on separate recording commands. That is, the AS can only instruct the MS to separately record the media flowing on each media leg: a recording for all the data coming from UAC1, and a different recording for all the data coming from UAC2. If someone subsequently wants to access the whole conversation, the AS may take at least two different approaches: It may mix the two recordings itself (e.g., by delegating it to an offline mixing entity) in order to obtain a single file containing the combination of the two recordings. This way, a simple playout as described in would suffice. Alternatively, it may take advantage of the mixing functionality provided by the MS itself. One way to do this is to create a hidden conference on the MS, attach the UAC as a passive participant to it, and play the separate recordings on the conference as announcements. This way, the UAC accessing the recording would experience both of the recordings at the same time. The second approach is considered in this section. The framework transaction as described in assumes that a recording has already been requested for both UAC1 and UAC2, that the phone call has ended, and that the AS has successfully received the URIs to both of the recordings from the MS. Such steps are not described again, since they would be quite similar to the steps described in . As mentioned previously, the idea is to use a properly constructed hidden conference to mix the two separate recordings on the fly and present them to the UAC. It is, of course, up to the AS to subsequently unjoin the user from the conference and destroy the conference itself once the playout of the recordings ends for any reason.

>| | | |--+ create | | | | conf & | | A2. 200 OK (conferenceid=Y) |<-+ its ID | |<<++++++++++++++++++++++++++++++++| | | | | | B1. CONTROL (join UAC3 & confY) | | |++++++++++++++++++++++++++++++++>>| | | |--+ join | | | | UAC & | | B2. 200 OK |<-+ confY | |<+++++++++++++++++++++++++++++++++| | | | |<<######################################################>>| | UAC3 is now a passive participant in the conference | |<<######################################################>>| | | | | | C1. CONTROL (play REC1 on confY) | | |++++++++++++++++++++++++++++++++>>| | | D1. CONTROL (play REC2 on confY) | | |++++++++++++++++++++++++++++++++>>| | | |--+ Start | | | | both | | | | of the | | | |dialogs | | C2. 200 OK |<-+ | |<<++++++++++++++++++++++++++++++++| | | D2. 200 OK | | |<<++++++++++++++++++++++++++++++++| | | | |<<########################################################| | The two recordings are mixed and played together to UAC | |<<########################################################| | | | | | E1. CONTROL () | | |<<++++++++++++++++++++++++++++++++| | | E2. 200 OK | | |++++++++++++++++++++++++++++++++>>| | | F1. CONTROL () | | |<<++++++++++++++++++++++++++++++++| | | F2. 200 OK | | |++++++++++++++++++++++++++++++++>>| | | | . . . . . . ]]> The diagram above assumes that a recording of both of the channels (UAC1 and UAC2) has already taken place. Later, when we desire to play the whole conversation to a new user, UAC3, the AS may take care of the presented transactions. The framework transaction steps are only apparently more complicated than those presented so far. The only difference, in fact, is that transactions C and D are concurrent, since the recordings must be played together. First of all, the AS creates a new conference to act as a mixing entity (A1). The settings for the conference are chosen according to the use case, e.g., the video layout, which is fixed to <dual-view>, and the switching type to <controller>. When the conference has been successfully created (A2), the AS takes note of the conference identifier. At this point, UAC3 is attached to the conference as a passive user (B1). There would be no point in letting the user contribute to the conference mix, since he will only need to watch a recording. In order to specify his passive status, both the audio and video streams for the user are set to 'recvonly'. If the transaction succeeds, the MS notifies the AS (B2). Once the conference has been created and UAC3 has been attached to it, the AS can request the playout of the recordings; in order to do so, it requests two concurrent <prompt> directives (C1 and D1), addressing the recording of UAC1 (REC1) and UAC2 (REC2), respectively. Both of the prompts must be played on the previously created conference and not to UAC3 directly, as can be deduced from the 'conferenceid' attribute of the <dialog> element. The transactions "live their lives" exactly as explained for previous <prompt> examples. The originating transactions are first prepared and started (C2, D2), and then, as soon as the playout ends, a related CONTROL message is triggered by the MS (E1, F1). This notification may contain a <promptinfo> element with information about how the playout proceeded (e.g., whether the playout completed normally or was interrupted by a DTMF tone, etc.).

MS (CFW CONTROL, createconference) -------------------------------------------- CFW 506e039f65bd CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 312

A2. AS <- MS (CFW 200 OK) ------------------------- CFW 506e039f65bd 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 151 B1. AS -> MS (CFW CONTROL, join) -------------------------------- CFW 09202baf0c81 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 214 B2. AS <- MS (CFW 200 OK) ------------------------- CFW 09202baf0c81 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 C1. AS -> MS (CFW CONTROL, play recording from UAC1) ---------------------------------------------------- CFW 3c2a08be4562 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 229 D1. AS -> MS (CFW CONTROL, play recording from UAC2) ---------------------------------------------------- CFW 1c268d810baa CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 229 C2. AS <- MS (CFW 200 OK) ------------------------- CFW 1c268d810baa 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 137 D2. AS <- MS (CFW 200 OK) ------------------------- CFW 3c2a08be4562 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 137 E1. AS <- MS (CFW CONTROL event, playout of recorded UAC1 ended) ---------------------------------------------------------------- CFW 77aec0735922 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 230 E2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 77aec0735922 200 F1. AS <- MS (CFW CONTROL event, playout of recorded UAC2 ended) ---------------------------------------------------------------- CFW 62726ace1660 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 230 F2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 62726ace1660 200 ]]>

One of the most important services the MS must be able to provide is mixing. This involves mixing media streams from different sources and delivering the resulting mix(es) to each interested party, often according to per-user policies, settings, and encoding. A typical scenario involving mixing is, of course, media conferencing. In such a scenario, the media sent by each participant is mixed, and each participant typically receives the overall mix, excluding its own contribution and encoded in the format it negotiated. This example points out in a quite clear way how mixing must take care of the profile of each involved entity. A media perspective of such a scenario is depicted in .

| Media |===================>| UAC | | A |<===================| Server |<===================| B | +-------+ B+C (RTP) +--------+ B (RTP) +-------+ ]]> From the framework point of view, when the UACs' legs are not attached to anything yet, what appears is shown in : since there are no connections involving the UACs yet, the frames they might be sending are discarded, and nothing is sent back to them (except for silence, if its transmission is requested).

>-------x x.......>>.....o o.....<<.......x x-------<<-----o | | | | | xx | | |. | +-------|.-------+ |. ^v ^v |. oo UAC C ]]> The next subsections will cover several typical scenarios involving mixing and conferencing as a whole, specifically: Simple Bridging scenario, which is a very basic (i.e., no "special effects"; just mixing involved) conference involving one or more participants. Rich Conference scenario, which enriches the Simple Bridging scenario by adding additional features typically found in conferencing systems (e.g., DTMF collection for PIN-based conference access, private and global announcements, recordings, and so on). Coaching scenario, which is a more complex scenario that involves per-user mixing (customers, agents, and coaches don't all get the same mixes). Sidebars scenario, which adds more complexity to the previous conferencing scenarios by involving sidebars (i.e., separate conference instances that only exist within the context of a parent conference instance) and the custom media delivery that follows. Floor Control scenario, which provides some guidance on how floor control could be involved in a MEDIACTRL-based media conference. All of the above-mentioned scenarios depend on the availability of a mixing entity. Such an entity is provided in the Media Control Channel Framework by the conferencing package. Besides allowing for the interconnection of media sources as seen in the Direct Echo Test section, this package enables the creation of abstract connections that can be joined to multiple connections. These abstract connections, called conferences, mix the contribution of each attached connection and feed them accordingly (e.g., a connection with a 'sendrecv' property would be able to contribute to the mix and listen to it, while a connection with a 'recvonly' property would only be able to listen to the overall mix but not actively contribute to it). That said, each of the above-mentioned scenarios will start more or less in the same way: by the creation of a conference connection (or more than one, as needed in some cases) to be subsequently referred to when it comes to mixing. A typical framework transaction to create a new conference instance in the Media Control Channel Framework is depicted in :

>| | |--+ create | | | conf and | 2. 200 OK (conferenceid=Y) |<-+ its ID |<<++++++++++++++++++++++++++++++++| map URI +--| | X with | | | confY +->| | | | . . . . ]]> The call flow is quite straightforward and can typically be summarized in the following steps: The AS invokes the creation of a new conference instance by means of a CONTROL request (1); this request is addressed to the conferencing package (msc-mixer/1.0) and contains in the body the directive (<createconference>) with all the desired settings for the new conference instance. In the example below, the mixing policy is to mix the five ('reserved-talkers') loudest speakers (nbest), while ten listeners at maximum are allowed. Video settings are configured, including the mechanism used to select active video sources (<controller>, meaning the AS will explicitly instruct the MS about it) and details about the video layouts to make available. In this example, the AS is instructing the MS to use a <single-view> layout when only one video source is active, to pass to a <quad-view> layout when at least two video sources are active, and to use a <multiple-5x1> layout whenever the number of sources is at least five. Finally, the AS also subscribes to the "active-talkers" event, which means it wants to be informed (at a rate of 4 seconds) whenever an active participant is speaking. The MS creates the conference instance, assigns a unique identifier to it (6146dd5), and completes the transaction with a 200 response (2). At this point, the requested conference instance is active and ready to be used by the AS. It is then up to the AS to integrate the use of this identifier in its application logic.

MS (CFW CONTROL) ------------------------- CFW 3032e5fb79a1 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 489

2. AS <- MS (CFW 200) --------------------- CFW 3032e5fb79a1 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 151 ]]>

As mentioned previously, the simplest way that an AS can use a conference instance is simple bridging. In this scenario, the conference instance just acts as a bridge for all the participants that are attached to it. The bridge takes care of transcoding, if needed (in general, different participants may use different codecs for their streams), echo cancellation (each participant will receive the overall mix, excluding its own contribution) and per-participant mixing (each participant may receive different mixed streams, according to what it needs/is allowed to send/receive). This assumes, of course, that each interested participant must be somehow joined to the bridge in order to indirectly communicate with the other participants. From the media perspective, the scenario can be seen as depicted in .

>-------+~~~>{##}:::>+:::::::>>:::::o o:::::<<:::::::+<:::{##}<~~~+-------<<-----o | ^: | | |v | | ++ | | |: | +--------|:-------+ |: ^v ^v |: oo UAC C ]]> In the framework, the first step is obviously to create a new conference instance as seen in the introductory section (). Assuming that a conference instance has already been created, bridging participants to it is quite straightforward and can be accomplished as seen in the Direct Echo Test scenario. The only difference here is that each participant is not directly connected to itself (Direct Echo) or another UAC (Direct Connection) but to the bridge instead. shows the example of two different UACs joining the same conference. The example, as usual, hides the previous interaction between each of the two UACs and the AS, and instead focuses on what the AS does in order to actually join the participants to the bridge so that they can interact in a conference. Please note also that to make the diagram more readable, two different identifiers (UAC1 and UAC2) are used in place of the identifiers previously employed to introduce the scenario (UAC A, B, C).

>| | | | |--+ join | | | | | UAC1 & | | | A2. 200 OK |<-+ confY | | |<<++++++++++++++++++++++++++++++++++| | | | | |<<######################################################>>| | Now UAC1 is mixed in the conference | |<<######################################################>>| | | | | | | | B1. CONTROL (join UAC2 and confY) | | | |++++++++++++++++++++++++++++++++++>>| | | | |--+ join | | | | | UAC2 & | | | B2. 200 OK |<-+ confY | | |<<++++++++++++++++++++++++++++++++++| | | | | | |<<###########################################>>| | | Now UAC2 too is mixed in the conference | | |<<###########################################>>| | | | | . . . . . . . . ]]> The framework transaction steps are actually quite trivial and easy to understand, since they're very similar to some previously described scenarios. The AS joins both UAC1 (id1 in A1) and UAC2 (id1 in B1) to the conference (id2 in both transactions). As a result of these two operations, both UACs are mixed in the conference. Since no <stream> is explicitly provided in any of the transactions, all the media from the UACs (audio/video) are attached to the conference (as long as the conference has been properly configured to support both, of course).

MS (CFW CONTROL) -------------------------- CFW 434a95786df8 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 120 A2. AS <- MS (CFW 200 OK) ------------------------- CFW 434a95786df8 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 B1. AS -> MS (CFW CONTROL) -------------------------- CFW 5c0cbd372046 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 120 B2. AS <- MS (CFW 200 OK) ------------------------- CFW 5c0cbd372046 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 ]]> Once one or more participants have been attached to the bridge, their connections and how their media are handled by the bridge can be dynamically manipulated by means of another directive, called <modifyjoin>. A typical use case for this directive is the change of direction of an existing media (e.g., a previously speaking participant is muted, which means its media direction changes from 'sendrecv' to 'recvonly'). shows how a framework transaction requesting such a directive might appear.

>| | | | |--+ modify | | | | | join | | | 2. 200 OK |<-+ settings | | |<<++++++++++++++++++++++++++++++++| | | | | |<<######################################################| | Now UAC1 can receive but not send (recvonly) | |<<######################################################| | | | | . . . . . . . . ]]> The directive used to modify an existing join configuration is <modifyjoin>, and its syntax is exactly the same as the syntax required in <join> instructions. In fact, the same syntax is used for identifiers (id1/id2). Whenever a <modifyjoin> is requested and id1 and id2 address one or more joined connections, the AS is requesting a change of the join configuration. In this case, the AS instructs the MS to mute (<stream> media=audio, direction=recvonly) UAC1 (id1=UAC1) in the conference (id2) it has been attached to previously. Any other connection existing between them is left untouched. It is worth noting that the <stream> settings are enforced according to both the provided direction AND the id1 and id2 identifiers. For instance, in this example id1 refers to UAC1, while id2 refers to the conference in the MS. This means that the required modifications have to be applied to the stream specified in the <stream> element of the message, along the direction that goes from 'id1' to 'id2' (as specified in the <modifyjoin> element of the message). In the provided example, the AS wants to mute UAC1 with respect to the conference. To do so, the direction is set to 'recvonly', meaning that, for what affects id1, the media stream is only to be received. If id1 referred to the conference and id2 to UAC1, to achieve the same result the direction would have to be set to 'sendonly', meaning "id1 (the conference) can only send to id2 (UAC1), and no media stream must be received". Additional settings for a <stream> (e.g., audio volume, region assignments, and so on) follow the same approach, as discussed in subsequent sections.

MS (CFW CONTROL) ------------------------- CFW 57f2195875c9 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 182 2. AS <- MS (CFW 200 OK) ------------------------ CFW 57f2195875c9 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 123 ]]>

The previous scenario can be enriched with additional features often found in existing conferencing systems. Typical examples include IVR-based menus (e.g., the DTMF collection for PIN-based conference access), partial and complete recordings in the conference (e.g., for the "state your name" functionality and recording of the whole conference), private and global announcements, and so on. All of this can be achieved by means of the functionality provided by the MS. In fact, even if the conferencing and IVR features come from different packages, the AS can interact with both of them and achieve complex results by correlating the effects of different transactions in its application logic. From the media and framework perspective, a typical Rich Conference scenario can be seen as depicted in .

>-------+~~~>{##}:::>+:::::::>>:::::o o:::::<<:::::::+<:::{##}<~~~+-------<<-----o | ^: | | | |v v | | ++ * (collect DTMF, get name) | |: | +--------|:--------+ |: ^v ^v |: oo UAC C ]]> To identify a single sample scenario, let's consider this sequence for a participant joining a conference (which again we assume has already been created): The UAC as usual INVITEs a URI associated with a conference, and the AS follows the previously explained procedure to have the UAC negotiate a new media session with the MS. The UAC is presented with an IVR menu, in which it is requested to input a PIN code to access the conference. If the PIN is correct, the UAC is asked to state its name so that it can be recorded. The UAC is attached to the conference, and the previously recorded name is announced globally to the conference to advertise its arrival. shows a single UAC joining a conference. The example, as usual, hides the previous interaction between the UAC and the AS, and instead focuses on what the AS does to actually interact with the participant and join it to the conference bridge.

>| | | |--+ start | | | | the | | A2. 200 OK |<-+ dialog | |<<++++++++++++++++++++++++++++++++| | | | |<<########################################################| | "Please input the PIN number to join the conference" | |<<########################################################| | | | |########################################################>>| | DTMF digits are collected |--+ get |########################################################>>| | DTMF | | |<-+ digits | | B1. CONTROL () | | |<<++++++++++++++++++++++++++++++++| | Compare DTMF +--| B2. 200 OK | | digits with | |++++++++++++++++++++++++++++++++>>| | the PIN number +->| | | | C1. CONTROL (record name) | | |++++++++++++++++++++++++++++++++>>| | | |--+ start | | | | the | | C2. 200 OK |<-+ dialog | |<<++++++++++++++++++++++++++++++++| | | | |<<########################################################| | "Please state your name after the beep" | |<<########################################################| | | | |########################################################>>| | Audio from the UAC is recorded (until timeout or DTMF) |--+ save |########################################################>>| | in a | | |<-+ file | | D1. CONTROL () | | |<<++++++++++++++++++++++++++++++++| | Store recorded +--| D2. 200 OK | | file to play | |++++++++++++++++++++++++++++++++>>| | announcement in +->| | | conference later | | | | E1. CONTROL (join UAC & confY) | | |++++++++++++++++++++++++++++++++>>| | | |--+ join | | | | UAC & | | E2. 200 OK |<-+ confY | |<+++++++++++++++++++++++++++++++++| | | | |<<######################################################>>| | UAC is now included in the mix of the conference | |<<######################################################>>| | | | | | F1. CONTROL (play name on confY) | | |++++++++++++++++++++++++++++++++>>| | | |--+ start | | | | the | | F2. 200 OK |<-+ dialog | |<<++++++++++++++++++++++++++++++++| | | | |<<########################################################| | Global announcement: "Simon has joined the conference" | |<<########################################################| | | | | | G1. CONTROL () | | |<<++++++++++++++++++++++++++++++++| | | G2. 200 OK | | |++++++++++++++++++++++++++++++++>>| | | | . . . . . . ]]> As can be deduced from the sequence diagram above, the AS, in its business logic, correlates the results of different transactions, addressed to different packages, to implement a conferencing scenario more complex than the Simple Bridging scenario previously described. The framework transaction steps are as follows: Since this is a private conference, the UAC is to be presented with a request for a password, in this case a PIN number. To do so, the AS instructs the MS (A1) to collect a series of DTMF digits from the specified UAC (connectionid=UAC). The request includes both a voice message (<prompt>) and the described digit collection context (<collect>). The PIN is assumed to be a 4-digit number, and so the MS has to collect 4 digits maximum (maxdigits=4). The DTMF digit buffer must be cleared before collecting (cleardigitbuffer=true), and the UAC can use the star key to restart the collection (escapekey=*), e.g., if the UAC is aware that he mistyped any of the digits and wants to start again. The transaction goes on as usual (A2), with the transaction being handled and notification of the dialog start being sent in a 200 OK. After that, the UAC is actually presented with the voice message and is subsequently requested to input the required PIN number. We assume that the UAC typed the correct PIN number (1234), which is reported by the MS to the AS by means of the usual MS-generated CONTROL event (B1). The AS correlates this event to the previously started dialog by checking the referenced dialogid (06d1bac) and acks the event (B2). It then extracts the information it needs from the event (in this case, the digits provided by the MS) from the <controlinfo> container (dtmf=1234) and verifies that it is correct. Since the PIN is correct, the AS can proceed to the next step, i.e., asking the UAC to state his name, in order to subsequently play the recording on the conference to report the new participant. Again, this is done with a request to the IVR package (C1). The AS instructs the MS to play a voice message ("state your name after the beep"), to be followed by a recording of only the audio from the UAC (in stream, media=audio/sendonly, while media=video/inactive). A beep must be played right before the recording starts (beep=true), and the recording must only last 3 seconds (maxtime=3s), since it is only needed as a brief announcement. Without delving again into the details of a recording-related transaction (C2), the AS finally gets the URI of the requested recording (D1, acked in D2). At this point, the AS attaches the UAC (id1) to the conference (id2), just as explained for the Simple Bridging scenario (E1/E2). Finally, to notify the other participants that a new participant has arrived, the AS requests a global announcement on the conference. This is a simple <prompt> request to the IVR package (F1), as explained in previous sections (e.g., , among others), but with a slight difference: the target of the prompt is not a connectionid (a media connection) but the conference itself (conferenceid=6146dd5). As a result of this transaction, the announcement would be played on all the media connections attached to the conference that are allowed to receive media from it. The AS specifically requests that two media files be played: the media file containing the recorded name of the new user as retrieved in D1 ("Simon..."). a pre-recorded media file explaining what happened ("... has joined the conference"). The transaction then follows its usual flow (F2), and the event that sends notification regarding the end of the announcement (G1, acked in G2) concludes the scenario.

MS (CFW CONTROL, collect) ----------------------------------- CFW 50e56b8d65f9 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 311 A2. AS <- MS (CFW 200 OK) ------------------------- CFW 50e56b8d65f9 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 137 B1. AS <- MS (CFW CONTROL event) -------------------------------- CFW 166d68a76659 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 272 B2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 166d68a76659 200 C1. AS -> MS (CFW CONTROL, record) ---------------------------------- CFW 61fd484f196e CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 373 C2. AS <- MS (CFW 200 OK) ------------------------- CFW 61fd484f196e 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 137 D1. AS <- MS (CFW CONTROL event) -------------------------------- CFW 3ec13ab96224 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 402 D2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 3ec13ab96224 200 E1. AS -> MS (CFW CONTROL, join) -------------------------------- CFW 261d188b63b7 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 120 E2. AS <- MS (CFW 200 OK) ------------------------- CFW 261d188b63b7 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 F1. AS -> MS (CFW CONTROL, play) -------------------------------- CFW 718c30836f38 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 334 F2. AS <- MS (CFW 200 OK) ------------------------- CFW 718c30836f38 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 137 G1. AS <- MS (CFW CONTROL event) -------------------------------- CFW 6485194f622f CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 229 G2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 6485194f622f 200 ]]>

Another typical conference-based use case is the so-called Coaching scenario. In such a scenario, a customer (called "A" in the following example) places a call to a business call center. An agent (B) is assigned to the customer. A coach (C), who cannot be heard by the customer, provides the agent with whispered suggestions about what to say. This scenario is also described in . As can be deduced from the scenario description, per-user policies for media mixing and delivery, i.e., who can hear what, are very important. The MS must make sure that only the agent can hear the coach's suggestions. Since this is basically a multiparty call (despite what the customer might be thinking), a mixing entity is needed in order to accomplish the scenario requirements. To summarize: The customer (A) must only hear what the agent (B) says. The agent (B) must be able to hear both A and the coach (C). C must be able to hear both A and B in order to give B the right suggestions and also be aware of the whole conversation. From the media and framework perspective, such a scenario can be seen as depicted in .

| Media |===================>| UAC | | A |<===================| Server |<===================| B | +-------+ B (RTP) +--------+ B (RTP) +-------+ ]]> From the framework point of view, when the previously mentioned legs are not attached to anything yet, what appears is shown in .

>-------x x.......>>.....o | | | | | | | | | xx | | .| + +------------v^-------------+ v^ .| .| oo UAC C ]]> By contrast, what the scenario should look like is depicted in . The customer receives media directly from the agent ('recvonly'), while all of the three involved participants contribute to a hidden conference. Of course, the customer is not allowed to receive the mixed flows from the conference ('sendonly'), unlike the agent and the coach, who must both be aware of the whole conversation ('sendrecv').

>-------+ | +------->>-----o | | v ^ | | +~~~~~~~>[##]::::>::::+ | | v^ | | || | | ++ | | :| + +------------v^-------------+ v^ :| :| oo UAC C ]]> In the framework, this can be achieved by means of the Mixer Control Package, which, as demonstrated in the previous conferencing examples, can be exploited whenever mixing and joining entities are needed. The needed steps can be summarized in the following list: First of all, a hidden conference is created. Then, the three participants are all attached to it, each with a custom mixing policy, specifically: the customer (A) as 'sendonly'. the agent (B) as 'sendrecv'. the coach (C) as 'sendrecv' and with a gain of -3 dB to halve the volume of its own contribution (so that the agent actually hears the customer at a louder volume and hears the coach whispering). Finally, the customer is joined to the agent as a passive receiver ('recvonly'). A diagram of such a sequence of transactions is depicted in :

>| | | | | |--+ create | | | | | | conf and | | | | A2. 200 OK (conferenceid=Y) |<-+ its ID | | | |<<++++++++++++++++++++++++++++++++| | | | | | | | | | B1. CONTROL (join A-->confY) | | | | |++++++++++++++++++++++++++++++++>>| | | | | |--+ join A | | | | | | & confY | | | | B2. 200 OK |<-+ sendonly | | | |<<++++++++++++++++++++++++++++++++| | | | | | |######################################################>>| | Customer (A) is mixed (sendonly) in the conference | |######################################################>>| | | | | | | | | | C1. CONTROL (join B<->confY) | | | | |++++++++++++++++++++++++++++++++>>| | | | | |--+ join B | | | | | | & confY | | | | C2. 200 OK |<-+ sendrecv | | | |<<++++++++++++++++++++++++++++++++| | | | | | | |<<#############################################>>| | | Agent (B) is mixed (sendrecv) in the conference | | |<##############################################>>| | | | | | | | | | D1. CONTROL (join C<->confY) | | | | |++++++++++++++++++++++++++++++++>>| | | | | |--+ join C | | | | | | & confY | | | | D2. 200 OK |<-+ sendrecv | | | |<<++++++++++++++++++++++++++++++++| | | | | | | | |<<######################################>>| | | | Coach (C) is mixed (sendrecv) as well | | | |<<######################################>>| | | | | | | | | | E1. CONTROL (join A<--B) | | | | |++++++++++++++++++++++++++++++++>>| | | | | |--+ join | | | | | | A & B | | | | E2. 200 OK |<-+ recvonly | | | |<<++++++++++++++++++++++++++++++++| | | | | | |<<######################################################| | Finally, Customer (A) is joined (recvonly) to Agent (B)| |<<######################################################| | | | | | . . . . . . . . . . ]]> First of all, the AS creates a new hidden conference by means of a <createconference> request (A1). This conference is properly configured according to the use it is assigned to, i.e., to mix all the involved parties accordingly. Since only three participants will be joined to it, 'reserved-talkers' is set to 3. 'reserved-listeners', on the other hand, is set to 2, since only the agent and the coach must receive a mix, while the customer must be unaware of the coach. Finally, the video layout is set to <dual-view> for the same reason, since only the customer and the agent must appear in the mix. The MS sends notification of the successful creation of the new conference in a 200 framework message (A2). The identifier assigned to the conference, which will be used in subsequent requests addressed to it, is 1df080e. Now that the conference has been created, the AS joins the three actors to it with different policies, namely (i) the customer (A) is joined as 'sendonly' to the conference (B1), (ii) the agent (B) is joined as 'sendrecv' to the conference (C1), and (iii) the coach (C) is joined as 'sendrecv' (but audio only) to the conference and with a lower volume (D1). The custom policies are enforced by means of properly constructed <stream> elements. The MS takes care of the requests and acks them (B2, C2, D2). At this point, the conference will receive media from all the actors but only provide the agent and the coach with the resulting mix. To complete the scenario, the AS joins A with B directly as 'recvonly' (E1). The aim of this request is to provide A with media too, namely the media contributed by B. This way, A is unaware of the fact that its media are accessed by C by means of the hidden mixer. The MS takes care of this request too and acks it (E2), concluding the scenario.

MS (CFW CONTROL, createconference) -------------------------------------------- CFW 238e1f2946e8 CONTROL Control-Package: msc-mixer Content-Type: application/msc-mixer+xml Content-Length: 329

A2. AS <- MS (CFW 200 OK) ------------------------- CFW 238e1f2946e8 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 151 B1. AS -> MS (CFW CONTROL, join) -------------------------------- CFW 2eb141f241b7 CONTROL Control-Package: msc-mixer Content-Type: application/msc-mixer+xml Content-Length: 226 B2. AS <- MS (CFW 200 OK) ------------------------- CFW 2eb141f241b7 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 C1. AS -> MS (CFW CONTROL, join) -------------------------------- CFW 515f007c5bd0 CONTROL Control-Package: msc-mixer Content-Type: application/msc-mixer+xml Content-Length: 122 C2. AS <- MS (CFW 200 OK) ------------------------- CFW 515f007c5bd0 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 D1. AS -> MS (CFW CONTROL, join) -------------------------------- CFW 0216231b1f16 CONTROL Control-Package: msc-mixer Content-Type: application/msc-mixer+xml Content-Length: 221 D2. AS <- MS (CFW 200 OK) ------------------------- CFW 0216231b1f16 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 E1. AS -> MS (CFW CONTROL, join) -------------------------------- CFW 140e0f763352 CONTROL Control-Package: msc-mixer Content-Type: application/msc-mixer+xml Content-Length: 236 E2. AS <- MS (CFW 200 OK) ------------------------- CFW 140e0f763352 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 ]]>

Within the context of conferencing, there could be a need for so&nbhy;called sidebars, or side conferences. This would be the case, for instance, if two or more participants of a conference were willing to create a side conference among each other while still receiving part of the original conference mix in the background. Motivations for such a use case can be found in both and . It is clear that in such a case the side conference is actually a separate conference but must also somehow be related to the original conference. Although the application-level relationship is out of scope for this document (this "belongs" to Centralized Conferencing (XCON)), the media stream relationship is more relevant here, because there is a stronger relationship at the media level from the MEDIACTRL point of view. Consequently, it is interesting to analyze how sidebars could be used to construct the conference mixes according to the MEDIACTRL specification. The scenario presented in this section is a conference hosting four different participants: A, B, C, and D. All these participants are attached to the conference as active senders and receivers of the existing media streams. At a certain point in time, two participants (B and D) decide to create a sidebar just for them. The sidebar they want to create is constructed so that only audio is involved. The audio mix of the sidebar must not be made available to the main conference. The mix of the conference must be attached to the sidebar, but with a lower volume (30%), because it is just background to the actual conversation. This would allow both B and D to talk to each other without A and C listening to them, while B and D could still have an overview of what's happening in the main conference. From the media and framework perspective, such a scenario can be seen as depicted in .

| Media |===================>| UAC | | A |<===================| Server |<===================| B | +-------+ C (RTP) +--------+ B (RTP) +-------+ ^ " " " B+[a+c] (RTP) " " D (RTP) " " " v +-------+ | UAC | | D | +-------+ ]]> From the framework point of view, when all the participants are attached to the main conference, what appears is shown in .

>-------+~~~>{##}:::>+:::::::>>:::::o o:::::<<:::::::+<:::{##}<~~~+-------<<-----o | ^: | | |v | | ++ | | |: | +--------|:-------+ |: ^v ^v |: oo UAC D ]]> By contrast, what the scenario should look like is depicted in . A new mixer is created to host the sidebar. The main mix is then attached as 'sendonly' to the sidebar mix at a lower volume (in order to provide the sidebar users with a background of the main conference). The two interested participants (B and D) have their audio leg detached from the main conference and attached to the sidebar. This detachment can be achieved by either actually detaching the leg or just modifying the status of the leg to 'inactive'. Note that this only affects the audio stream: the video of the two users is still attached to the main conference, and what happens at the application level may or may not have been changed accordingly (e.g., XCON protocol interactions). Please note that the main conference is assumed to be in place and the involved participants (A, B, C, and D) attached ('sendrecv') to it.

>-------+~~~>{##}:::>{##}:::>+:::::::>>:::::o o:::::<<:::::::+<:::{##} {##}<~~~+-------<<-----o | ^: | | ++ | | |v | +----------------|:--------+ |: ^v ^v |: oo UAC D ]]> The situation may subsequently be reverted (e.g., destroying the sidebar conference and reattaching B and D to the main conference mix) in the same way. The AS would just need to unjoin B and D from the hidden conference and change their connection with the main conference back to 'sendrecv'. After unjoining the main mix and the sidebar mix, the sidebar conference could then be destroyed. For brevity, and because similar transactions have already been presented, these steps are not described here. In the framework, just as in the previous section, the presented scenario can again be achieved by means of the Mixer Control Package. The needed steps can be summarized in the following list: First of all, a hidden conference is created (the sidebar mix). Then, the main conference mix is attached to it as 'sendonly' and with a gain of -5 dB to limit the volume of its own contribution to 30% (so that B and D can hear each other at a louder volume while still listening to what's happening in the main conference in the background). B and D are detached from the main mix for audio (<modifyjoin> with 'inactive' status). B and D are attached to the hidden sidebar mix for audio. Note that for detaching B and D from the main mix, a <modifyjoin> with an 'inactive' status is used, instead of an <unjoin>. The motivation for this is related to how a subsequent rejoining of B and D to the main mix could take place. In fact, by using <modifyjoin> the resources created when first joining B and D to the main mix remain in place, even if marked as unused at the moment. An <unjoin>, on the other hand, would actually free those resources, which in turn could be granted to other participants joining the conference in the meantime. This means that when needing to reattach B and D to the main mix, the MS may not have the resources to do so, resulting in an undesired failure. A diagram of such a sequence of transactions (where confX is the identifier of the pre-existing main conference mix) is depicted in :

>| | | | |--+ create | | | | | conf and | | | A2. 200 OK (conferenceid=Y) |<-+ its ID | | |<<++++++++++++++++++++++++++++++++| | | | | | | | B1. CONTROL (join confX-->confY) | | | |++++++++++++++++++++++++++++++++>>| | | | |--+ join confX | | | | | & confY | | | B2. 200 OK |<-+ sendonly | | |<<++++++++++++++++++++++++++++++++| (30% vol) | | | | | | | C1. CONTROL (modjoin B---confX) | | | |++++++++++++++++++++++++++++++++>>| | | | |--+ modjoin B | | | | | & confX | | | C2. 200 OK |<-+ (inactive) | | |<<++++++++++++++++++++++++++++++++| | | | | | | | D1. CONTROL (join B<-->confY) | | | |++++++++++++++++++++++++++++++++>>| | | | |--+ join B | | | | | & confY | | | D2. 200 OK |<-+ sendrecv | | |<<++++++++++++++++++++++++++++++++| (audio) | | | | |<<##################################################>>| | Participant B is mixed (sendrecv) in the sidebar | | (A, C, and D can't listen to her/him anymore) | |<<##################################################>>| | | | | | | | E1. CONTROL (modjoin D---confX) | | | |++++++++++++++++++++++++++++++++>>| | | | |--+ modjoin D | | | | | & confX | | | E2. 200 OK |<-+ (inactive) | | |<<++++++++++++++++++++++++++++++++| | | | | | | | F1. CONTROL (join D<-->confY) | | | |++++++++++++++++++++++++++++++++>>| | | | |--+ join D | | | | | & confY | | | F2. 200 OK |<-+ sendrecv | | |<<++++++++++++++++++++++++++++++++| (audio) | | | | | |<<########################################>>| | | D is mixed (sendrecv) in the sidebar too | | | (A and C can't listen to her/him anymore) | | |<<########################################>>| | | | . . . . . . ]]> First of all, the hidden conference mix is created (A1). The request is basically the same as that presented in previous sections, i.e., a <createconference> request addressed to the Mixer package. The request is very lightweight and asks the MS to only reserve two listener seats ('reserved-listeners', since only B and D have to hear something) and three talker seats ('reserved&nbhy;listeners', because in addition to B and D the main mix is also an active contributor to the sidebar). The mixing will be driven by directives from the AS (mix-type=controller). When the mix is successfully created, the MS provides the AS with its identifier (519c1b9). As a first transaction after that, the AS joins the audio from the main conference and the newly created sidebar conference mix (B1). Only audio needs to be joined (media=audio), with a 'sendonly' direction (i.e., only flowing from the main conference to the sidebar and not vice versa) and at 30% volume with respect to the original stream (setgain=-5 dB). A successful completion of the transaction is reported to the AS (B2). At this point, the AS makes the connection of B (2133178233:18294826) and the main conference (2f5ad43) inactive by means of a <modifyjoin> directive (C1). The request is taken care of by the MS (C2), and B is actually excluded from the mix for sending as well as receiving. After that, the AS (D1) joins B (2133178233:18294826) to the sidebar mix created previously (519c1b9). The MS attaches the requested connections and sends confirmation to the AS (D2). The same transactions already done for B are done for D as well (id1=1264755310:2beeae5b), i.e., the <modifyjoin> to make the connection in the main conference inactive (E1-2) and the <join> to attach D to the sidebar mix (F1-2). At the end of these transactions, A and C will only listen to each other, while B and D will listen to each other and to the conference mix as a comfortable background.

MS (CFW CONTROL, createconference) -------------------------------------------- CFW 7fdcc2331bef CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 198

A2. AS <- MS (CFW 200 OK) ------------------------- CFW 7fdcc2331bef 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 151 B1. AS -> MS (CFW CONTROL, join with setgain) --------------------------------------------- CFW 4e6afb6625e4 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 226 B2. AS <- MS (CFW 200 OK) ------------------------- CFW 4e6afb6625e4 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 C1. AS -> MS (CFW CONTROL, modifyjoin with 'inactive' status) ----------------------------------------------------------- CFW 3f2dba317c83 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 193 C2. AS <- MS (CFW 200 OK) ------------------------- CFW 3f2dba317c83 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 123 D1. AS -> MS (CFW CONTROL, join to sidebar) ------------------------------------------- CFW 2443a8582d1d CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 181 D2. AS <- MS (CFW 200 OK) ------------------------- CFW 2443a8582d1d 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 E1. AS -> MS (CFW CONTROL, modifyjoin with 'inactive' status) ----------------------------------------------------------- CFW 436c6125628c CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 193 E2. AS <- MS (CFW 200 OK) ------------------------- CFW 436c6125628c 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 123 F1. AS -> MS (CFW CONTROL, join to sidebar) ------------------------------------------- CFW 7b7ed00665dd CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 181 F2. AS <- MS (CFW 200 OK) ------------------------- CFW 7b7ed00665dd 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 125 ]]>

As described in , floor control is a feature typically needed and employed in most conference scenarios. In fact, while not a mandatory feature to implement when realizing a conferencing application, it provides additional control of the media streams contributed by participants, thus allowing for moderation of the available resources. The Centralized Conferencing (XCON) framework suggests the use of the Binary Floor Control Protocol (BFCP) to achieve the aforementioned functionality. That said, a combined use of floor control functionality and the tools made available by the MEDIACTRL specification for conferencing would definitely be interesting to investigate. introduces two different approaches to integrating floor control with the MEDIACTRL architecture: (i) a topology where the floor control server is co&nbhy;located with the AS and (ii) a topology where the floor control server is co-located with the MS. The two approaches are obviously different with respect to the amount of information the AS and the MS have to deal with, especially when thinking about the logic behind the floor queues and automated decisions. Nevertheless, considering how the Media Control Channel Framework is conceived, approach (ii) would need a dedicated package (be it an extension or a totally new package) in order to make the MS aware of floor control and allow the MS to interact with the interested UAC accordingly. At the time of writing, such a package doesn't exist yet, and as a consequence only approach (i) will be dealt with in the presented scenario. The scenario will then assume that the Floor Control Server (FCS) is co-located with the AS. This means that all the BFCP requests will be sent by Floor Control Participants (FCPs) to the FCS, which will make the AS directly aware of the floor statuses. For the sake of simplicity, the scenario assumes that the involved participants are already aware of all the identifiers needed in order to make BFCP requests for a specific conference. Such information may have been carried according to the COMEDIA negotiation as specified in . It is important to note that such information must not reach the MS. This means that within the context of the 3PCC mechanism that may have been used in order to attach a UAC to the MS, all the BFCP-related information negotiated by the AS and the UAC must be removed before making the negotiation available to the MS, which may be unable to understand the specification. A simplified example of how this could be achieved is presented in . Please note that within the context of this example scenario, different identifiers may be used to address the same entity. Specifically, in this case the UAC (the endpoint sending and receiving media) is also a FCP, as it negotiates a BFCP channel too.

| | | | INVITE (SDP: RTP) | | |-------------------------------->| | | 200 (SDP: RTP'+labels) | | |<--------------------------------| | match +--| | | floors | | | | & labels +->| | | | | | 200 (SDP: RTP'+BFCP'+labels) | | |<--------------------------------| | | ACK | | |-------------------------------->| | | | ACK | | |-------------------------------->| | | | |<<###################### RTP MEDIA STREAMS ######################>>| | | | |<<******** BFCP CHANNEL *******>>| | | | | . . . . . . ]]> From the media and framework perspective, such a scenario doesn't differ much from the conferencing scenarios presented earlier. It is more interesting to focus on the chosen topology for the scenario, as depicted in .

| (FCS) |<****** BFCP *******>| (FCC) | +-------+ +--------+ +-------+ ^ ^ | | | CFW | | | | v | +--------+ +----------RTP---------->| MS | +--------+ ]]> The AS, besides maintaining the already-known SIP signaling among the involved parties, also acts as the FCS for the participants in the conferences for which it is responsible. In the scenario, two Floor Control Participants are involved: a basic Participant (FCP) and a Chair (FCC). As in all of the previously described conferencing examples, in the framework this can be achieved by means of the Mixer Control Package. Assuming that the conference has been created, the participant has been attached ('recvonly') to it, and the participant is aware of the involved BFCP identifiers, the needed steps can be summarized in the following list: The assigned chair, FCC, sends a subscription for events related to the floor for which it is responsible (FloorQuery). The FCP sends a BFCP request (FloorRequest) to access the audio resource ("I want to speak"). The FCS (AS) sends a provisional response to the FCP (FloorRequestStatus PENDING) and handles the request in its queue. Since a chair is assigned to this floor, the request is forwarded to the FCC for a decision (FloorStatus). The FCC makes a decision and sends it to the FCS (ChairAction ACCEPTED). The FCS takes note of the decision and updates the queue accordingly. The decision is sent to the FCP (FloorRequestStatus ACCEPTED). The floor has not been granted yet. As soon as the queue allows it, the floor is actually granted to the FCP. The AS, which is co-located with the FCS, understands in its business logic that such an event is associated with the audio resource being granted to the FCP. As a consequence, a <modifyjoin> ('sendrecv') is sent through the Control Channel to the MS in order to unmute the FCP UAC in the conference. The FCP is notified of this event (FloorRequestStatus GRANTED), thus ending the scenario. A diagram of such a sequence of transactions (also involving the BFCP message flow at a higher level) is depicted in :

>| | | | |--+ handle | | | | | subscription | | | |<-+ | | | FloorStatus | | |<<*******| | | | | | | FloorRequest | | |*****************>>| | | | |--+ handle | | | | | request | | Pending |<-+ (queue) | |<<*****************| | | | | | | | FloorStatus | | |<<*******| | | | | | | | ChairAction (ACCEPT) | | |*******>>| | | | ChairActionAck | | |<<*******| | | | |--+ handle | | | | | decision | | | |<-+ (queue) | | Accepted | | |<<*****************| | | | FloorStatus | | |<<*******| | | | | | | | |--+ queue | | | | | grants | | | |<-+ floor | | | | | | | | 1. CONTROL (modjoin UAC<->conf) | | | |++++++++++++++++++++++++++++++++>>| | | | |--+ modjoin | | | | | UAC & conf | | | 2. 200 OK |<-+ (sendrecv) | | |<<++++++++++++++++++++++++++++++++| | | | | |<<##################################################>>| | UAC1 is now unmuted (sendrecv) in the conference | | and can speak, contributing to the mix | |<<##################################################>>| | | | | | Granted | | |<<*****************| | | | FloorStatus | | |<<*******| | | | | | . . . . . . ]]> As can easily be deduced from the above diagram, the complex interaction at the BFCP level only results in a single transaction at the MEDIACTRL level. In fact, the purpose of the BFCP transactions is to moderate access to the audio resource, which means providing the event trigger to MEDIACTRL-based conference manipulation transactions. Before being granted the floor, the FCP UAC is excluded from the conference mix at the MEDIACTRL level ('recvonly'). As soon as the floor has been granted, the FCP UAC is included in the mix. In MEDIACTRL words: Since the FCP UAC must be included in the audio mix, a <modifyjoin> is sent to the MS in a CONTROL directive. The <modifyjoin> has as identifiers the connectionid associated with the FCP UAC (e1e1427c:1c998d22) and the conferenceid of the mix (cf45ee2). The <stream> element tells the MS that the audio media stream between the two must become bidirectional ('sendrecv'), changing the previous status ('recvonly'). Please note that in this case only audio was involved in the conference; if video were involved as well, and video had to be unchanged, a <stream> directive for video had to be placed in the request as well in order to maintain its current status.

MS (CFW CONTROL) ------------------------- CFW gh67ffg56w21 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 182 2. AS <- MS (CFW 200 OK) ------------------------ CFW gh67ffg56w21 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 123 ]]>

This section includes additional scenarios that can be of interest when dealing with AS<->MS flows. The aim of the following subsections is to present the use of features peculiar to the IVR package: specifically, variable announcements, VCR (video cassette recorder) prompts, parallel playback, recurring dialogs, and custom grammars. To describe how call flows involving such features might happen, three sample scenarios have been chosen: Voice Mail (variable announcements for digits, VCR controls). Current Time (variable announcements for date and time, parallel playback). DTMF-driven Conference Manipulation (recurring dialogs, custom grammars).

An application that typically uses the services an MS can provide is Voice Mail. In fact, while it is clear that many of its features are part of the application logic (e.g., the mapping of a URI with a specific user's voice mailbox, the list of messages and their properties, and so on), the actual media work is accomplished through the MS. Features needed by a Voice Mail application include the ability to record a stream and play it back at a later time, give verbose announcements regarding the status of the application, control the playout of recorded messages by means of VCR controls, and so on. These features are all supported by the MS through the IVR package. Without delving into the details of a full Voice Mail application and all its possible use cases, this section will cover a specific scenario and try to deal with as many interactions as possible that may happen between the AS and the MS in such a context. This scenario, depicted as a sequence diagram in , will be as follows: The UAC INVITEs a URI associated with his mailbox, and the AS follows the previously explained procedure to have the UAC negotiate a new media session with the MS. The UAC is first prompted with an announcement giving him the amount of available new messages in the mailbox. After that, the UAC can choose which message to access by sending a DTMF tone. The UAC is then presented with a VCR-controlled announcement, in which the chosen received mail is played back to him. VCR controls allow him to navigate through the prompt. This is a quite oversimplified scenario, considering that it doesn't even allow the UAC to delete old messages or organize them but just to choose which received message to play. Nevertheless, it gives us the chance to deal with variable announcements and VCR controls -- two typical features that a Voice Mail application would almost always take advantage of. Other features that a Voice Mail application would rely upon (e.g., recording streams, event-driven IVR menus, and so on) have been introduced in previous sections, and so representing them would be redundant. This means that the presented call flows assume that some messages have already been recorded and are available at reachable locations. The example also assumes that the AS has placed the recordings in its own storage facilities, since it is not safe to rely upon the internal MS storage, which is likely to be temporary.

>| | | | prepare & | | |--+ start | | | | the | | A2. 200 OK |<-+ dialog | |<<++++++++++++++++++++++++++++++++| | | | |<<########################################################| | "You have five messages ..." | |<<########################################################| | | | | | B1. CONTROL () | | |<<++++++++++++++++++++++++++++++++| | | B2. 200 OK | | |++++++++++++++++++++++++++++++++>>| | | | | | C1. CONTROL (VCR for chosen msg) | | |++++++++++++++++++++++++++++++++>>| | | | prepare & | | |--+ start | | | | the | | C2. 200 OK |<-+ dialog | |<<++++++++++++++++++++++++++++++++| | | | |<<########################################################| | "Hi there, I tried to call you but..." |--+ |<<########################################################| | handle | | | | VCR- |########################################################>>| | driven | The UAC controls the playout using DTMF | | (DTMF) |########################################################>>| |playout | | |<-+ | | D1. CONTROL () | | |<<++++++++++++++++++++++++++++++++| | | D2. 200 OK | | |++++++++++++++++++++++++++++++++>>| | | | . . . . (other events are received in the meantime) | . . . | | E1. CONTROL () | | |<<++++++++++++++++++++++++++++++++| | | E2. 200 OK | | |++++++++++++++++++++++++++++++++>>| | | | . . . . . . ]]> The framework transaction steps are as follows: The first transaction (A1) is addressed to the IVR package (msc-ivr). It is basically an 'promptandcollect' dialog, but with a slight difference: some of the prompts to play are actual audio files, for which a URI is provided (media loc="xxx"), while others are so-called <variable> prompts; these <variable> prompts are actually constructed by the MS itself according to the directives provided by the AS. In this example, the sequence of prompts requested by the AS is as follows: play a wav file ("you have..."). play a digit ("five...") by building it (variable: digit=5). play a wav file ("messages..."). A DTMF collection is requested as well (<collect>) to be taken after the prompts have been played. The AS is only interested in a single digit (maxdigits=1). The transaction is handled by the MS, and if everything works fine (i.e., the MS retrieved all the audio files and successfully built the variable announcements), the dialog is started; its start is reported, together with the associated identifier (5db01f4) to the AS in a terminating 200 OK message (A2). The AS then waits for the dialog to end in order to retrieve the results in which it is interested (in this case, the DTMF tone the UAC chooses, since it will affect which message will have to be played subsequently). The UAC hears the prompts and chooses a message to play. In this example, he wants to listen to the first message and so inputs "1". The MS intercepts this tone and notifies the AS of it in a newly created CONTROL event message (B1); this CONTROL includes information about how each single requested operation ended (<promptinfo> and <collectinfo>). Specifically, the event states that the prompt ended normally (termmode=completed) and that the subsequently collected tone is 1 (dtmf=1). The AS acks the event (B2), since the dialogid provided in the message is the same as that of the previously started dialog. At this point, the AS uses the value retrieved from the event to proceed with its business logic. It decides to present the UAC with a VCR-controllable playout of the requested message. This is done with a new request to the IVR package (C1), which contains two operations: <prompt> to address the media file to play (an old recording) and <control> to instruct the MS about how the playout of this media file shall be controlled via DTMF tones provided by the UAC (in this example, different DTMF digits are associated with different actions, e.g., pause/resume, fast forward, rewind, and so on). The AS also subscribes to DTMF events related to this control operation (matchmode=control), which means that the MS is to trigger an event any time that a DTMF associated with a control operation (e.g., 7=pause) is intercepted. The MS prepares the dialog and, when the playout starts, sends notification in a terminating 200 OK message (C2). At this point, the UAC is presented with the prompt and can use DTMF digits to control the playback. As explained previously, any DTMF associated with a VCR operation is then reported to the AS, together with a timestamp stating when the event happened. An example is provided (D1) in which the UAC pressed the fast-forward key (6) at a specific time. Of course, as for any other MS-generated event, the AS acks it (D2). When the playback ends (whether because the media reached its termination or because any other interruption occurred), the MS triggers a concluding event with information about the whole dialog (E1). This event, besides including information about the prompt itself (<promptinfo>), also includes information related to the VCR operations (<controlinfo>), that is, all the VCR controls the UAC used (fast forward/rewind/pause/resume in this example) and when it happened. The final ack by the AS (E2) concludes the scenario.

MS (CFW CONTROL, play and collect) -------------------------------------------- CFW 2f931de22820 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 429 A2. AS <- MS (CFW 200 OK) ------------------------- CFW 2f931de22820 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 137 B1. AS <- MS (CFW CONTROL event) -------------------------------- CFW 7c97adc41b3e CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 270 B2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 7c97adc41b3e 200 C1. AS -> MS (CFW CONTROL, VCR) ------------------------------- CFW 3140c24614bb CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 423 C2. AS <- MS (CFW 200 OK) ------------------------- CFW 3140c24614bb 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 137 D1. AS <- MS (CFW CONTROL event, dtmfnotify) -------------------------------------------- CFW 361840da0581 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 179 D2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 361840da0581 200 [..] The other VCR DTMF notifications are skipped for brevity [..] E1. AS <- MS (CFW CONTROL event, dialogexit) -------------------------------------------- CFW 3ffab81c21e9 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 485 E2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 3ffab81c21e9 200 ]]>

An interesting scenario to create with the help of features provided by the MS is what is typically called 'Current Time'. A UAC calls a URI, which presents the caller with the current date and time. As can easily be deduced by the very nature of the application, variable announcements play an important role in this scenario. In fact, rather than having the AS build an announcement according to the current time using different framework messages, it is much easier to rely upon the "variable announcements" mechanism provided by the IVR package, as variable announcements provide several ways to deal with dates and times. To make the scenario more interesting and have it cover more functionality, the application is also assumed to have background music played during the announcement. Because most of the announcements will be variable, a means is needed to have more streams played in parallel on the same connection. This can be achieved in two different ways: two separate and different dialogs, playing the variable announcements and the background track, respectively. a single dialog implementing a parallel playback. The first approach assumes that the available MS implements implicit mixing, which may or may not be supported since it's a recommended feature but not mandatory. The second approach assumes that the MS implements support for more streams of the same media type (in this case audio) in the same dialog, which, exactly as for the case of implicit mixing, is not to be taken for granted. Because the first approach is quite straightforward and easy to understand, the following scenario uses the second approach and assumes that the available MS supports parallel playback of more audio tracks within the context of the same dialog. That said, the covered scenario, depicted as a sequence diagram in , will be as follows: The UAC INVITEs a URI associated with the Current Time application, and the AS follows the previously explained procedure to have the UAC negotiate a new media session with the MS. The UAC is presented with an announcement including (i) a voice stating the current date and time; (ii) a background music track; and (iii) a mute background video track.

>| prepare | | |--+ and | | A2. 202 | | start | |<<++++++++++++++++++++++++++++++++| | the | | | | dialog | | | | (takes | | A3. REPORT (terminate) |<-+ time) | |<<++++++++++++++++++++++++++++++++| | | A4. 200 OK | | |++++++++++++++++++++++++++++++++>>| | | | |<<########################################################| | "16th of december 2008, 5:31 PM..." | |<<########################################################| | | | | | B1. CONTROL () | | |<<++++++++++++++++++++++++++++++++| | | B2. 200 OK | | |++++++++++++++++++++++++++++++++>>| | | | . . . . . . . . . ]]> The framework transaction steps are as follows: The first transaction (A1) is addressed to the IVR package (msc-ivr); it is basically an 'playannouncements' dialog, but, unlike all the scenarios presented so far, it includes directives for a parallel playback, as indicated by the <par> element. There are three flows to play in parallel: a sequence (<seq>) of variable and static announcements (the actual time and date). a music track ('media=music.wav') to be played in the background at a lower volume (soundLevel=50%). a mute background video track (media=clock.mpg). The global announcement ends when the longest of the three parallel steps ends (endsync=last). This means that if one of the steps ends before the others, the step is muted for the rest of the playback. In this example, the series of static and <variable> announcements is requested by the AS: play a wav file ("Tuesday..."). play a date ("16th of december 2008...") by building it (variable: date with a ymd=year/month/day format). play a time ("5:31 PM...") by building it (variable: time with a t12=12 hour day format, am/pm). The transaction is extended by the MS (A2) with a new timeout, as in this case the MS needs some more time to retrieve all the needed media files. Should the new timeout expire as well, the MS would send a further message to extend it again (a REPORT update), but for the sake of simplicity we assume that in this scenario it is not needed. If everything went fine (i.e., the MS retrieved all the audio files and successfully built the variable announcements, and it supports parallel playback as requested), the dialog is started. Its start is reported, together with the associated identifier (415719e), to the AS in a terminating REPORT message (A3). The AS acks the REPORT (A4) and waits for the dialog to end in order to either conclude the application or proceed to further steps if required by the application itself. When the last of the three parallel announcements ends, the dialog terminates, and an event (B1) is triggered to the AS with the relevant information (promptinfo). The AS acks (B2) and terminates the scenario.

MS (CFW CONTROL, play) -------------------------------- CFW 0c7680191bd2 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 506 A2. AS <- MS (CFW 202) ---------------------- CFW 0c7680191bd2 202 Timeout: 5 A3. AS <- MS (CFW REPORT terminate) ----------------------------------- CFW 0c7680191bd2 REPORT Seq: 1 Status: terminate Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 137 A4. AS -> MS (CFW 200, ACK to 'REPORT terminate') ------------------------------------------------- CFW 0c7680191bd2 200 Seq: 1 B1. AS <- MS (CFW CONTROL event) -------------------------------- CFW 4481ca0c4fca CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 229 B2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 4481ca0c4fca 200 ]]>

To complete the scenarios presented in , this section deals with how the AS can use the MS to detect DTMF tones from conference participants and take actions on the conference accordingly. A typical example is when participants in a conference are provided with specific codes to: mute/unmute themselves in the conference; change their volume in the conference, or the volume of the conference itself; change the video layout in the conference, if allowed; kick abusive users out of the conference; and so on. To achieve all this, the simplest thing an AS can do is to prepare a recurring DTMF collection for each participant with specific grammars to match. If the collected tones match the grammar, the MS would notify the AS of the tones and start the collection again. Upon receipt of <collectinfo> events, the AS would in turn originate the proper related request, e.g., a <modifyjoin> on the participant's stream with the conference. This is made possible by three features provided by the IVR package: the 'repeatCount' attribute. the subscription mechanism. the Speech Recognition Grammar Specification (SRGS) . The first feature allows recurring instances of the same dialog without the need for additional requests upon completion of the dialog itself. In fact, the 'repeatCount' attribute indicates how many times the dialog has to be repeated. When the attribute has the value 0, it means that the dialog has to be repeated indefinitely, meaning that it's up to the AS to destroy it by means of a <dialogterminate> request when the dialog is no longer needed. The second feature allows the AS to subscribe to events related to the IVR package without waiting for the dialog to end, e.g., matching DTMF collections in this case. Finally, the last feature allows custom matching grammars to be specified. This way, only a subset of the possible DTMF strings can be specified, so that only those matches in which the AS is interested are reported. Grammars other than SRGS may be supported by the MS and will achieve the same result. This document will only describe the use of an SRGS grammar, since support for SRGS is mandated in . To identify a single sample scenario, we assume that a participant has successfully joined a conference, e.g., as detailed in . We also assume that the following codes are to be provided within the conference to participants in order to let them take advantage of advanced features: *6 to mute/unmute themselves (on/off trigger). *1 to lower their own volume in the conference and *3 to raise it. *7 to lower the volume of the conference stream they are receiving and *9 to raise it. *0 to leave the conference. This means that six different codes are supported and are to be matched in the requested DTMF collection. All other codes are collected by the MS but discarded, and no event is triggered to the AS. Because all the codes have the '*' (star) DTMF code in common, the following is an example of an SRGS grammar that may be used in the request by the AS:

0 1 3 6 7 9

* ]]> As can be deduced by looking at the grammar, the presented SRGS XML code specifies exactly the requirements for the collections to match. The rule is to match any string that has a star ('*') followed by a single supported digit (0, 1, 3, 6, 7, or 9). Such grammar, as stated in , may be either provided inline in the request itself or referenced externally by means of the 'src' attribute. In the example scenario, we'll put it inline, but an external reference to the same document would achieve exactly the same result. shows how the AS might request the recurring collection for a UAC. As before, the example assumes that the UAC is already a participant in the conference.

>| | | |--+ start | | | | the | | A2. 200 OK |<-+ dialog | |<<++++++++++++++++++++++++++++++++++++| | | | |########################################################>>| | Recurring DTMF digit collection starts |--+ get |########################################################>>| | DTMF | | |<-+ digits | | B1. CONTROL (dtmfinfo=*1) | | |<<++++++++++++++++++++++++++++++++++++| | | B2. 200 OK |--+ get | |++++++++++++++++++++++++++++++++++++>>| | DTMF | | |<-+ digits | | C1. CONTROL (modifyjoin UAC1-->conf) | | |++++++++++++++++++++++++++++++++++++>>| | | |--+ modify | | | | UAC | | C2. 200 OK |<-+ volume | |<<++++++++++++++++++++++++++++++++++++| | | | |########################################################>>| | Volume of UAC in conference is lowered | |########################################################>>| | | | | | D1. CONTROL (dtmfinfo=*9) | | |<<++++++++++++++++++++++++++++++++++++| | | D2. 200 OK |--+ get | |++++++++++++++++++++++++++++++++++++>>| | DTMF | | |<-+ digits | | E1. CONTROL (modifyjoin UAC1<--conf) | | |++++++++++++++++++++++++++++++++++++>>| | | |--+ modify | | | | conf | | E2. 200 OK |<-+ volume | |<<++++++++++++++++++++++++++++++++++++| | | | |<<########################################################| | Now UAC can hear the conference mix at a higher volume | |<<########################################################| | | | | | F1. CONTROL (dtmfinfo=*6) | | |<<++++++++++++++++++++++++++++++++++++| | | F2. 200 OK |--+ get | |++++++++++++++++++++++++++++++++++++>>| | DTMF | | |<-+ digits | | G1. CONTROL (modifyjoin UAC1-->conf) | | |++++++++++++++++++++++++++++++++++++>>| | | |--+ mute | | | | UAC in | | G2. 200 OK |<-+ conf | |<<++++++++++++++++++++++++++++++++++++| | | | |########################################################>>| | UAC is now muted in the conference | |########################################################>>| | | | | | H1. CONTROL (dtmfinfo=*0) | | |<<++++++++++++++++++++++++++++++++++++| | | H2. 200 OK |--+ get | |++++++++++++++++++++++++++++++++++++>>| | DTMF | | |<-+ digits | | I1. CONTROL (destroy DTMF dialog) | | |++++++++++++++++++++++++++++++++++++>>| | | |--+ delete | | | | the | | I2. 200 OK |<-+ dialog | |<<++++++++++++++++++++++++++++++++++++| (DTMF | | |collection | | | stops) | | J1. CONTROL (dialogexit) | | |<<++++++++++++++++++++++++++++++++++++| | | J2. 200 OK | | |++++++++++++++++++++++++++++++++++++>>| | | | |########################################################>>| | No more tones from UAC are collected | |########################################################>>| | | | | | K1. CONTROL (unjoin UAC1<-X->conf) | | |++++++++++++++++++++++++++++++++++++>>| | | |--+ unjoin | | | | UAC & | | K2. 200 OK |<-+ conf | |<<++++++++++++++++++++++++++++++++++++| | | | | | L1. CONTROL (unjoin-notify) | | |<<++++++++++++++++++++++++++++++++++++| | | L2. 200 OK | | |++++++++++++++++++++++++++++++++++++>>| | | | . . . . . . ]]> As can be deduced from the sequence diagram above, the AS, in its business logic, correlates the results of different transactions, addressed to different packages, to implement a more complex conferencing scenario. In fact, <dtmfnotify> events are used to take actions according to the functions of the DTMF codes. The framework transaction steps are as follows: The UAC is already in the conference, and so the AS starts a recurring collect with a grammar to match. This is done by placing a CONTROL request addressed to the IVR package (A1). The operation to implement is a <collect>, and we are only interested in two-digit DTMF strings (maxdigits). The AS is not interested in a DTMF terminator (termchar is set to a non-conventional DTMF character), and the DTMF escape key is set to '#' (the default is '*', which would conflict with the code syntax for the conference and so needs to be changed). A custom SRGS grammar is provided inline (<grammar> with mode=dtmf). The whole dialog is to be repeated indefinitely (dialog has repeatCount=0), and the AS wants to be notified when matching collections occur (dtmfsub with matchmode=collect). The request is handled by the MS (A2) and then successfully started (dialogid=01d1b38). This means that the MS has started collecting DTMF tones from the UAC. The MS collects a matching DTMF string from the UAC (*1). Since the AS subscribed to this kind of event, a CONTROL event notification (dtmfnotify) is triggered by the MS (B1), including the collected tones. Since the dialog is recurring, the MS immediately restarts the collection. The AS acks the event (B2) and in its business logic understands that the code '*1' means that the UAC wants its own volume to be lowered in the conference mix. The AS is able to associate the event with the right UAC by referring to the attached dialogid (01d1b38). It then acts accordingly by sending a <modifyjoin> (C1) that does exactly this: the provided <stream> child element instructs the MS to modify the volume of the UAC-->conference audio flow (setgain=-5 dB 'sendonly'). Note that the "setgain" value is the absolute volume level. If the user's request is to lower the volume level, the AS must remember the previously set volume level and from it calculate the new volume level. Note how the request also includes directives for the inverse direction. This verbose approach is needed; otherwise, the MS would not only change the volume in the requested direction but would also disable the media flow in the other direction. Having a proper <stream> addressing the UAC<--conf media flow as well ensures that this doesn't happen. The MS successfully enforces the requested operation (C2), changing the volume. A new matching DTMF string from the UAC is collected (*9). As before, an event is triggered to the AS (D1). The AS acks the event (D2) and matches the new code ('*9') with its related operation (raise the volume of the conference mix for the UAC), taking the proper action. A different <modifyjoin> is sent (E1) with the new instructions (setgain=+3 dB 'recvonly'). The same considerations regarding how the incremental operation should be mapped to the command apply here as well. Note also how a <stream> for the inverse direction ('sendonly') is again provided just as a placeholder, which basically instructs the MS that the settings for that direction are not to be changed, maintaining the previous directives of (C1). The MS successfully enforces this requested operation as well (E2), changing the volume in the specified direction. At this point, a further matching DTMF string from the UAC is collected (*6) and sent to the AS (F1). After the required ack (F2), the AS reacts by implementing the action associated with the new code ('*6'), by which the UAC requested that it be muted within the conference. A new <modifyjoin> is sent (G1) with a properly constructed payload (setstate=mute 'sendonly'), and the MS enforces it (G2). A last (in this scenario) matching DTMF string is collected by the MS (*0). As with all the previous codes, notification of this string is sent to the AS (H1). The AS acks the event (H2) and understands that the UAC wants to leave the conference now (since the code is *0). This means that a series of actions must be taken: The recurring collection is stopped, since it's no longer needed. The UAC is unjoined from the conference it is in. Additional operations might be considered, e.g., a global announcement stating that the UAC is leaving, but for the sake of conciseness such operations are not listed here. The former is accomplished by means of a <dialogterminate> request (I1) to the IVR package (dialogid=01d1b38) and the latter by means of an <unjoin> request (K1) to the Mixer package. The <dialogterminate> request is handled by the MS (I2), and the dialog is terminated successfully. As soon as the dialog has actually been terminated, a <dialogexit> event is triggered as well to the AS (J1). This event has no report of the result of the last iteration (since the dialog was terminated abruptly with an immediate=true) and is acked by the AS (J2) to finally complete the dialog lifetime. The <unjoin> request is immediately enforced (K2). As a consequence of the unjoin operation, an <unjoin-notify> event notification is triggered by the MS (L1) to confirm to the AS that the requested entities are no longer attached to each other. The status in the event is set to 0, which, as stated in the specification, means that the join has been terminated by an <unjoin> request. The ack from the AS (L2) concludes this scenario.

MS (CFW CONTROL, recurring collect with grammar) ---------------------------------------------------------- CFW 238e1f2946e8 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 809 A2. AS <- MS (CFW 200 OK) ------------------------- CFW 238e1f2946e8 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 137 B1. AS <- MS (CFW CONTROL dtmfnotify event) ------------------------------------------- CFW 1dd62e043c00 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 180 B2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 1dd62e043c00 200 C1. AS -> MS (CFW CONTROL, modifyjoin with setgain) --------------------------------------------------- CFW 0216231b1f16 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 290 C2. AS <- MS (CFW 200 OK) ------------------------- CFW 0216231b1f16 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 123 D1. AS <- MS (CFW CONTROL dtmfnotify event) ------------------------------------------- CFW 4d674b3e0862 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 180 D2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 4d674b3e0862 200 E1. AS -> MS (CFW CONTROL, modifyjoin with setgain) --------------------------------------------------- CFW 140e0f763352 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 292 E2. AS <- MS (CFW 200 OK) ------------------------- CFW 140e0f763352 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 123 F1. AS <- MS (CFW CONTROL dtmfnotify event) ------------------------------------------- CFW 478ed6f1775b CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 180 F2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 478ed6f1775b 200 G1. AS -> MS (CFW CONTROL, modifyjoin with setstate) ---------------------------------------------------- CFW 7fdcc2331bef CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 295 G2. AS <- MS (CFW 200 OK) ------------------------- CFW 7fdcc2331bef 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 123 H1. AS <- MS (CFW CONTROL dtmfnotify event) ------------------------------------------- CFW 750b917a5d4a CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 180 H2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 750b917a5d4a 200 I1. AS -> MS (CFW CONTROL, dialogterminate) ------------------------------------------- CFW 515f007c5bd0 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 128 I2. AS <- MS (CFW 200 OK) ------------------------- CFW 515f007c5bd0 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 140 J1. AS <- MS (CFW CONTROL dialogexit event) ------------------------------------------- CFW 76adc41122c1 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 155 J2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 76adc41122c1 200 K1. AS -> MS (CFW CONTROL, unjoin) ---------------------------------- CFW 4e6afb6625e4 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 127 K2. AS <- MS (CFW 200 OK) ------------------------- CFW 4e6afb6625e4 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 122 L1. AS <- MS (CFW CONTROL unjoin-notify event) ---------------------------------------------- CFW 577696293504 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 157

L2. AS -> MS (CFW 200, ACK to 'CONTROL event') ---------------------------------------------- CFW 577696293504 200 ]]>

All the flows presented so far describe the interaction between a single AS and a single MS. This is the simplest topology that can be envisaged in a MEDIACTRL-compliant architecture, but it's not the only topology that is allowed. presents several possible topologies that potentially involve several AS and several MS as well. To properly allow for such topologies, an additional element called the Media Resource Broker (MRB) has been introduced in the MEDIACTRL architecture. Such an entity, and the protocols needed to interact with it, has been standardized in . An MRB is basically a locator that is aware of a pool of MS and makes them available to interested AS according to their requirements. For this reason, two different interfaces have been introduced: the Publishing interface (), which allows an MRB to subscribe for notifications at the MS it is handling (e.g., available and occupied resources, current state, etc.). the Consumer interface (), which allows an interested AS to query an MRB for an MS capable of fulfilling its requirements. The flows in the following sections will present some typical use-case scenarios involving an MRB and the different topologies in which it has been conceived to work. Additionally, a few considerations on the handling of media dialogs whenever an MRB is involved are presented in .

An MRB uses the MS's Publishing interface to acquire relevant information. This Publishing interface, as specified in , is made available as a Control Package for the Media Control Channel Framework. This means that in order to receive information from an MS, an MRB must negotiate a Control Channel as explained in . This package allows an MRB to either request information in the form of a direct request/answer from an MS or subscribe for events. Of course, since the MRB is interested in the Publishing interface, the previously mentioned negotiation must be changed in order to take into account the need for the MRB Control Package. The name of this package is 'mrb-publish/1.0', which means that the SYNC might look like the following:

MS (CFW SYNC) ----------------------- CFW 6b8b4567327b SYNC Dialog-ID: z9hG4bK-4542-1-0 Keep-Alive: 100 Packages: msc-ivr/1.0,msc-mixer/1.0,mrb-publish/1.0 2. MRB <- MS (CFW 200) ---------------------- CFW 6b8b4567327b 200 Keep-Alive: 100 Packages: msc-ivr/1.0,msc-mixer/1.0,mrb-publish/1.0 Supported: msc-example-pkg/1.0 ]]> The meaning of this negotiation was presented previously. It is enough to point out that the MRB in this case adds a new item to the 'Packages' it needs support for (mrb-publish/1.0). In this case, the MS supports it, and in fact it is added to the negotiated packages in the reply:

The MS as described in , on the other hand, did not have support for that package, since only 'msc-example-pkg/1.0' was part of the 'Supported' list. presents a ladder diagram of a typical interaction based on the MRB Control Package.

| | A2. 200 OK | |<---------------------------------------------| | |--+ collect | | | requested | |<-+ info | B1. CONTROL (MRB notification) | |<---------------------------------------------| | B2. 200 OK | |--------------------------------------------->| | | . . . . | | | |--+ collect | | | up-to-date | |<-+ info | C1. CONTROL (MRB notification) | |<---------------------------------------------| | C2. 200 OK | |--------------------------------------------->| | | . . . . | | | D1. CONTROL (Update MRB subscription) | |--------------------------------------------->| | D2. 200 OK | |<---------------------------------------------| | | . . . . ]]> In this example, the MRB subscribes for information at the specified MS, and events are triggered on a regular, negotiated basis. All of these messages flow through the Control Channel, as do all of the messages discussed in this document. The framework transaction steps are as follows: The MRB sends a new CONTROL message (A1) addressed to the MRB package (mrb-publish/1.0); it is a subscription for information (<subscription>), and the MRB is asking to be notified at least every 10 minutes (<minfrequency>) or, if required, every 30 seconds at maximum. The subscription must last 30 minutes (<expires>), after which no additional notifications must be sent. The MS acknowledges the request (A2) and sends notification of the success of the request in a 200 OK message (<mrbresponse>). The MS prepares and sends the first notification to the MRB (B1). As has been done with other packages, the notification has been sent as an MS-generated CONTROL message; it is a notification related to the request in the first message, because the 'id' (p0T65U) matches that request. All of the information that the MRB subscribed for is provided in the payload. The MRB acknowledges the notification (B2) and uses the retrieved information to update its own information as part of its business logic. The previous step (the MRB acknowledges notifications and uses the retrieved information) repeats at the required frequency, with up&nbhy;to-date information. After a while, the MRB updates its subscription (D1) to get more frequent updates (minfrequency=1, an update every second at least). The MS accepts the update (D2), although it may adjust the frequency in the reply according to its policies (e.g., a lower rate, such as minfrequency=30). The notifications continue, but at the newer rate; the expiration is also updated accordingly (600 seconds again, since the update refreshes it).

MS (CONTROL, publish request) ---------------------------------------- CFW lidc30BZObiC CONTROL Control-Package: mrb-publish/1.0 Content-Type: application/mrb-publish+xml Content-Length: 337 60 600 30 A2. MRB <- MS (200 to CONTROL, request accepted) ------------------------------------------------ CFW lidc30BZObiC 200 Timeout: 10 Content-Type: application/mrb-publish+xml Content-Length: 139 B1. MRB <- MS (CONTROL, event notification from MS) --------------------------------------------------- CFW 03fff52e7b7a CONTROL Control-Package: mrb-publish/1.0 Content-Type: application/mrb-publish+xml Content-Length: 4157

a1b2c3d4

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TestbedPrototype

msc-ivr/1.0

\ nbest \

\ single-view \

\ dual-view \

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\ dual-view-2x1-crop \

\ quad-view \

\ multiple-5x1 \

\ multiple-3x3 \

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cg/*

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conftn/*

IT Campania Napoli Via Claudio 21 University of Napoli Federico II Dipartimento di Informatica e Sistemistica 80210

TestbedPrototype-01

sip:MediaServer@ms.example.net

B2. MRB -> MS (200 to CONTROL) ------------------------------ CFW 03fff52e7b7a 200 (C1 and C2 omitted for brevity) D1. MRB -> MS (CONTROL, publish request) ---------------------------------------- CFW pyu788fc32wa CONTROL Control-Package: mrb-publish/1.0 Content-Type: application/mrb-publish+xml Content-Length: 342 600 1 D2. MRB <- MS (200 to CONTROL, request accepted) ------------------------------------------------ CFW pyu788fc32wa 200 Timeout: 10 Content-Type: application/mrb-publish+xml Content-Length: 332 600 30 ]]>

Whereas the Publishing interface is used by an MS to publish its functionality and up-to-date information to an MRB, the Consumer interface is used by an interested AS to access a resource. An AS can use the Consumer interface to contact an MRB and describe the resources it needs. The MRB then replies with the needed information: specifically, the address of an MS that is capable of meeting the requirements. However, unlike the Publishing interface, the Consumer interface is not specified as a Control Package. Rather, it is conceived as an XML-based protocol that can be transported by means of either HTTP or SIP, as will be shown in the following sections. As specified in , the Consumer interface can be involved in two topologies: Query mode and Inline mode. In the Query mode (), the Consumer requests and responses are conveyed by means of HTTP. Once the AS gets the answer, the usual MEDIACTRL interactions occur between the AS and the MS chosen by the MRB. By contrast, in the Inline mode, the MRB is in the path between the AS and the pool of MS it is handling. In this case, an AS can place Consumer requests using SIP as a transport, by means of a multipart payload () containing the Consumer request itself and an SDP related either to the creation of a Control Channel or to a UAC media dialog. This is called Inline-aware mode, since it assumes that the interested AS knows that an MRB is in place and knows how to talk to it. The MRB is also conceived to work with AS that are unaware of its functionality, i.e., unaware of the Consumer interface. In this kind of scenario, the Inline mode is still used, but with the AS thinking the MRB it is talking to is actually an MS. This approach is called Inline-unaware mode ().

As discussed in the previous section, in the Query mode the AS sends Consumer requests by means of HTTP. Specifically, an HTTP POST is used to convey the request. The MRB is assumed to send its response by means of an HTTP 200 OK reply. Since a successful Consumer response contains information to contact a specific MS (the MS the MRB has deemed most capable of fulfilling the AS's requirements), an AS can subsequently directly contact the MS, as described in . This means that in the Query mode the MRB acts purely as a locator, and then the AS and the MS can talk 1:1. presents a ladder diagram of a typical Consumer request in the Query topology:

| | | | | | |--+ Parse request | | | and see if any | |<-+ MS applies | | | 2. 200 OK (Consumer response) | |<---------------------------------------------| | | |--+ Parse response and | | | start session (SIP/COMEDIA/CFW) | |<-+ with MS reported by MRB | | | . . . . ]]> In this example, the AS is interested in an MS meeting a defined set of requirements. The MS must: support both the IVR and Mixer packages. provide at least 10 G.711 encoding/decoding RTP sessions for IVR purposes. support HTTP-based streaming and support for the audio/x-wav file format in the IVR package. These requirements are properly formatted according to the MRB Consumer syntax. The framework transaction steps are as follows: The AS sends an HTTP POST message to the MRB (1). The payload is, of course, the Consumer request, which is reflected by the Content-Type header (application/mrb-consumer+xml). The Consumer request (<mediaResourceRequest>, uniquely identified by its 'id' attribute set to the random value 'n3un93wd'), includes some general requirements (<generalInfo>) and some IVR-specific requirements (<ivrInfo>). The general part of the requests contains the set of required packages (<packages>). The IVR-specific section contains requirements concerning the number of required IVR sessions (<ivr-sessions>), the file formats that are to be supported (<file-formats>), and the required file transfer capabilities (<file-transfer-modes>). The MRB gets the request and parses it. Then, according to its business logic, it realizes it can't find a single MS capable of targeting the request and as a consequence picks two MS instances that can handle 60 and 40 of the requested sessions, respectively. It prepares a Consumer response (2) to provide the AS with the requested information. The response (<mediaResourceResponse>, which includes the same 'id' attribute as the request) indicates success (status=200) and includes the relevant information (<response-session-info>). Specifically, the response includes transaction-related information (the same session-id and seq provided by the AS in its request, to allow proper request/response matching) together with information on the duration of the reservation (expires=3600, i.e., after an hour the request will expire) and the SIP addresses of the chosen MS. Note how the sequence number the MRB returned is not 1. According to the MRB specification, this is the starting value to increment for the sequence number to be used in subsequent requests. This means that should the AS want to update or remove the session it should use 10 as a value for the sequence number in the related request. According to Section 12 of , this random value for the first sequence number is also a way to help prevent a malicious entity from messing with or disrupting another AS session with the MRB. In fact, sequence numbers in requests and responses have to match, and failure to provide the correct sequence number would result in session failure and a 405 error message.

MRB (HTTP POST, Consumer request) ------------------------------------------ POST /Mrb/Consumer HTTP/1.1 Content-Length: 893 Content-Type: application/mrb-consumer+xml Host: mrb.example.com:8080 Connection: Keep-Alive User-Agent: Apache-HttpClient/4.0.1 (java 1.5) msc-ivr/1.0 msc-mixer/1.0

100 100

2. AS <- MRB (200 to POST, Consumer response) --------------------------------------------- HTTP/1.1 200 OK X-Powered-By: Servlet/2.5 Server: Sun GlassFish Communications Server 1.5 Content-Type: application/mrb-consumer+xml;charset=ISO-8859-1 Content-Length: 1146 Date: Thu, 28 Jul 2011 10:34:45 GMT

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]]> For the sake of conciseness, the subsequent steps are not presented. They are very trivial, since they basically consist of the AS issuing a COMEDIA negotiation with either of the obtained MS, as already presented in . The same can be said with respect to attaching UAC media dialogs. In fact, since after the Query the AS<->MS interaction becomes 1:1, UAC media dialogs can be redirected directly to the proper MS using the 3PCC approach, e.g., as shown in .

Unlike the Query mode, in the Inline-Aware MRB Mode (IAMM) the AS sends Consumer requests by means of SIP. Of course, saying that the transport changes from HTTP to SIP is not as trivial as it seems. In fact, HTTP and SIP behave in very different ways, and this is reflected in the way the Inline-aware mode is conceived. An AS willing to issue a Consumer request by means of SIP has to do so by means of an INVITE. As specified in , the payload of the INVITE can't contain only the Consumer request itself. In fact, the Consumer request is assumed to be carried within a SIP transaction. A Consumer session is not strictly associated with the lifetime of any SIP transaction, meaning that Consumer requests belonging to the same session may be transported over different SIP messages; therefore, a hangup on any of these SIP dialogs would not affect a Consumer session. That said, as documented in , envisages two kinds of SIP dialogs over which a Consumer request may be sent: a SIP control dialog (a SIP dialog sent by the AS in order to set up a Control Channel) and a UAC media dialog (a SIP dialog sent by the AS in order to attach a UAC to an MS). In both cases, the AS would prepare a multipart/mixed payload to achieve both ends, i.e., receiving a reply to its Consumer request and effectively carrying on the negotiation described in the SDP payload. The behaviors in the two cases, which are called the CFW-based approach and the media dialog-based approach, respectively, are only slightly different, but both will be presented to clarify how they could be exploited. To make things clearer for the reader, the same Consumer request as the Consumer request presented in the Query mode will be sent, in order to clarify how the behavior of the involved parties may differ.

presents a ladder diagram of a typical Consumer request in the CFW-based Inline-aware topology:

| | | 2. 100 (Trying) | | |<----------------------| | | |--+ Extract SDP and | | | | MRB payloads; handle | | |<-+ Consumer request to | | | pick MS | | | | | | 3. INVITE | | | (application/cfw from 1.) | | |-------------------------->| | | 4. 100 (Trying) | | |<--------------------------| | | |--+ Negotiate | | | | CFW Control | | |<-+ Channel | | 5. 200 OK | | | (application/cfw from MS) | | |<--------------------------| | | 6. ACK | | |-------------------------->| | Prepare new +--| | | payload with | | | | SDP from MS and +->| | | Consumer reply | | | | | | 7. 200 OK | | | (multipart/mixed: | | | application/cfw from MS, | | application/mrb-consumer+xml) | |<----------------------| | | 8. ACK | | |---------------------->| | | | | |--+ Read Consumer | | | | reply and use SDP | | |<-+ to create CFW Chn. | | | | | | | |<<############## TCP CONNECTION #################>>| | | | CFW SYNC | |++++++++++++++++++++++++++++++++++++++++++++++++++>| | | . . . . . . ]]> To make the scenario easier to understand, we assume that the AS is interested in exactly the same set of requirements as those presented in . This means that the Consumer request originated by the AS will be the same as before, with only the transport/topology changing. Please note that to make the protocol contents easier to read, a simple 'Part' is used whenever a boundary for a multipart/mixed payload is provided, instead of the actual boundary that would be inserted in the SIP messages. The framework transaction steps (for simplicity's sake, only the payloads, and not the complete SIP transactions, are reported) are as follows:

MRB (INVITE multipart/mixed) ------------------------------------- [..] Content-Type: multipart/mixed;boundary="Part" --Part Content-Type: application/sdp v=0 o=- 2890844526 2890842807 IN IP4 as.example.com s=MediaCtrl c=IN IP4 as.example.com t=0 0 m=application 48035 TCP cfw a=connection:new a=setup:active a=cfw-id:vF0zD4xzUAW9 --Part Content-Type: application/mrb-consumer+xml msc-ivr/1.0 msc-mixer/1.0

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--Part 3. MRB -> MS (INVITE SDP only) ------------------------------ [..] Content-Type: application/sdp v=0 o=- 2890844526 2890842807 IN IP4 as.example.com s=MediaCtrl c=IN IP4 as.example.com t=0 0 m=application 48035 TCP cfw a=connection:new a=setup:active a=cfw-id:vF0zD4xzUAW9 5. MRB <- MS (200 OK SDP) ------------------------- [..] Content-Type: application/sdp v=0 o=lminiero 2890844526 2890842808 IN IP4 ms.example.net s=MediaCtrl c=IN IP4 ms.example.net t=0 0 m=application 7575 TCP cfw a=connection:new a=setup:passive a=cfw-id:vF0zD4xzUAW9 7. AS <- MRB (200 OK multipart/mixed) ------------------------------------- [..] Content-Type: multipart/mixed;boundary="Part" --Part Content-Type: application/sdp v=0 o=lminiero 2890844526 2890842808 IN IP4 ms.example.net s=MediaCtrl c=IN IP4 ms.example.net t=0 0 m=application 7575 TCP cfw a=connection:new a=setup:passive a=cfw-id:vF0zD4xzUAW9 --Part Content-Type: application/mrb-consumer+xml

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--Part ]]> The sequence diagram and the dumps effectively show the different approach with respect to the Query mode. The SIP INVITE sent by the AS (1.) includes both a Consumer request (the same as before) and an SDP to negotiate a CFW channel with an MS. The MRB takes care of the request exactly as before (provisioning two MS instances) but with a remarkable difference: first of all, it picks one of the two MS instances on behalf of the AS (negotiating the Control Channel in steps 3 to 6) and only then replies to the AS with both the MS side of the SDP negotiation (with information on how to set up the Control Channel) and the Consumer response itself. The Consumer response is also slightly different in the first place. In fact, as can be seen in 7., there's an additional element (<connection-id>) that the MRB has added to the message. This element contains the 'connection-id' that the AS and MS would have built out of the 'From' and 'To' tags as explained in , had the AS contacted the MS directly. Since the MRB has actually done the negotiation on behalf of the AS, without this information the AS and MS would refer to different connectionid attributes to target the same dialog, thus causing the CFW protocol not to behave as expected. This aspect will be more carefully described in the next section (for the media dialog-based approach), since the 'connection-id' attribute is strictly related to media sessions. As before, for the sake of conciseness the subsequent steps of the previous transaction are quite trivial and therefore are not presented. In fact, as shown in the flow, the SIP negotiation has resulted in both the AS and the chosen MS negotiating a Control Channel. This means that the AS is only left to instantiate the Control Channel and send CFW requests according to its application logic. It is worthwhile to highlight the fact that, as in the Query example, the AS gets the addresses of both of the chosen MS in this example as well, since a Consumer transaction has taken place. This means that, just as in the Query case, any UAC media dialog can be redirected directly to the proper MS using the 3PCC approach, e.g., as shown in , rather than again using the MRB as a Proxy/B2BUA. Of course, a separate SIP control dialog would be needed before attempting to use the second MS instance.

There's a second way to take advantage of the IAMM mode, i.e., exploiting SIP dialogs related to UAC media dialogs as 'vessels' for Consumer messages. As will be made clearer in the following sequence diagram and protocol dumps, this scenario does not differ much from the scenario presented in with respect to the Consumer request/response, but it may be useful to compare these two scenarios and show how they may differ with respect to the management of the media dialog itself and any CFW Control Channel that may be involved. presents a ladder diagram of a typical Consumer request in the media dialog-based Inline-aware topology:

| | | | 2. 100 Trying | | | |<--------------| | | | | 3. INVITE | | | | (multipart/mixed: | | | | audio/video from 1., | | | | application/mrb-consumer+xml) | | |---------------------->| | | | 4. 100 (Trying) | | | |<----------------------| | | | |--+ Extract SDP and | | | | | MRB payloads; handle | | | |<-+ Consumer request to | | | | pick Media Servers | | | | | | | | 5. INVITE | | | | (audio/video from 3.) | | | |------------------------->| | | | 6. 100 (Trying) | | | |<-------------------------| | | | +--| | | | Handle media dialog | | | | | (connection-id) +->| | | | | | | | 7. 200 OK | | | | (audio/video from MS) | | | |<-------------------------| | | | 8. ACK | | | |------------------------->| | | Prepare new +--| | | | payload with | | | | | SDP from MS and +->| | | | Consumer reply | | | | | | | | 9. 200 OK | | | | (multipart/mixed: | | | | audio/video from MS, | | | application/mrb-consumer+xml) | | |<----------------------| | | | 10. ACK | | | |---------------------->| | | | | | | |--+ Read Consumer | | | | | reply and send | | | |<-+ SDP back to UAC | | | 11. 200 OK | | | |(audio/video from MS) | | |<--------------| | | | 12. ACK | | | |-------------->| | | | | | | |<<*************************** RTP ******************************>>| | | | | | |--+ Negotiate | | | | | CFW channel | | | |<-+ towards MS | | | | (if needed) | | . . . . . . . . | | | | | |<<############## TCP CONNECTION ################>>| | | | | | CFW SYNC | | |+++++++++++++++++++++++++++++++++++++++++++++++++>| | | | . . . . . . . . ]]> To make the scenario easier to understand, we assume that the AS is interested in exactly the same set of requirements as those presented in . This means that the Consumer request originated by the AS will be the same as before, with only the transport/topology changing. Again, please note that to make the protocol contents easier to read, a simple 'Part' is used whenever a boundary for a multipart/mixed payload is provided, instead of the actual boundary that would be inserted in the SIP messages. The framework transaction steps (for simplicity's sake, only the relevant headers and payloads, and not the complete SIP transactions, are reported) are as follows:

AS (INVITE with media SDP) ------------------------------------ [..] From: ;tag=1153573888 To: [..] Content-Type: application/sdp v=0 o=lminiero 123456 654321 IN IP4 203.0.113.2 s=A conversation c=IN IP4 203.0.113.2 t=0 0 m=audio 7078 RTP/AVP 0 3 8 101 a=rtpmap:0 PCMU/8000/1 a=rtpmap:3 GSM/8000/1 a=rtpmap:8 PCMA/8000/1 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-11 m=video 9078 RTP/AVP 98 3. AS -> MRB (INVITE multipart/mixed) ------------------------------------- [..] From: ;tag=fd4fush5 To: [..] Content-Type: multipart/mixed;boundary="Part" --Part Content-Type: application/sdp v=0 o=lminiero 123456 654321 IN IP4 203.0.113.2 s=A conversation c=IN IP4 203.0.113.2 t=0 0 m=audio 7078 RTP/AVP 0 3 8 101 a=rtpmap:0 PCMU/8000/1 a=rtpmap:3 GSM/8000/1 a=rtpmap:8 PCMA/8000/1 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-11 m=video 9078 RTP/AVP 98 --Part Content-Type: application/mrb-consumer+xml msc-ivr/1.0 msc-mixer/1.0

100 100

--Part 5. MRB -> MS (INVITE SDP only) ------------------------------ [..] From: ;tag=32pbdxZ8 To: [..] Content-Type: application/sdp v=0 o=lminiero 123456 654321 IN IP4 203.0.113.2 s=A conversation c=IN IP4 203.0.113.2 t=0 0 m=audio 7078 RTP/AVP 0 3 8 101 a=rtpmap:0 PCMU/8000/1 a=rtpmap:3 GSM/8000/1 a=rtpmap:8 PCMA/8000/1 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-11 m=video 9078 RTP/AVP 98 7. MRB <- MS (200 OK SDP) ------------------------- [..] From: ;tag=32pbdxZ8 To: ;tag=KQw677BF [..] Content-Type: application/sdp v=0 o=lminiero 123456 654322 IN IP4 203.0.113.1 s=MediaCtrl c=IN IP4 203.0.113.1 t=0 0 m=audio 63442 RTP/AVP 0 3 8 101 a=rtpmap:0 PCMU/8000 a=rtpmap:3 GSM/8000 a=rtpmap:8 PCMA/8000 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-15 a=ptime:20 a=label:7eda834 m=video 33468 RTP/AVP 98 a=rtpmap:98 H263-1998/90000 a=fmtp:98 CIF=2 a=label:0132ca2 9. AS <- MRB (200 OK multipart/mixed) ------------------------------------- [..] From: ;tag=fd4fush5 To: ;tag=117652221 [..] Content-Type: multipart/mixed;boundary="Part" --Part Content-Type: application/sdp v=0 o=lminiero 123456 654322 IN IP4 203.0.113.1 s=MediaCtrl c=IN IP4 203.0.113.1 t=0 0 m=audio 63442 RTP/AVP 0 3 8 101 a=rtpmap:0 PCMU/8000 a=rtpmap:3 GSM/8000 a=rtpmap:8 PCMA/8000 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-15 a=ptime:20 a=label:7eda834 m=video 33468 RTP/AVP 98 a=rtpmap:98 H263-1998/90000 a=fmtp:98 CIF=2 a=label:0132ca2 --Part Content-Type: application/mrb-consumer+xml

z1skKYZQ3eFu

9 3600

32pbdxZ8:KQw677BF

60 60

40 40

--Part 11. UAC <- AS (200 OK SDP) -------------------------- [..] From: ;tag=1153573888 To: ;tag=bcd47c32 [..] Content-Type: application/sdp v=0 o=lminiero 123456 654322 IN IP4 203.0.113.1 s=MediaCtrl c=IN IP4 203.0.113.1 t=0 0 m=audio 63442 RTP/AVP 0 3 8 101 a=rtpmap:0 PCMU/8000 a=rtpmap:3 GSM/8000 a=rtpmap:8 PCMA/8000 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-15 a=ptime:20 a=label:7eda834 m=video 33468 RTP/AVP 98 a=rtpmap:98 H263-1998/90000 a=fmtp:98 CIF=2 a=label:0132ca2 ]]> The first obvious difference is that the first INVITE (1.) is not originated by the AS itself (the AS was willing to set up a Control Channel in the previous example) but by an authorized UAC (e.g., to take advantage of a media service provided by the AS). As such, the first INVITE only contains an SDP to negotiate an audio and video channel. The AS in its business logic needs to attach this UAC to an MS according to some specific requirements (e.g., the called URI is associated to a specific service) and as such prepares a Consumer request to be sent to the MRB in order to obtain a valid MS for that purpose. As before, the Consumer request is sent together with the SDP to the MRB (3.). The MRB extracts the Consumer payload and takes care of it as usual; it picks two MS instances and attaches the UAC to the first MS instance (5.). Once the MS has successfully negotiated the audio and video streams (7.), the MRB takes note of the 'connection-id' associated with this call (which will be needed afterwards in order to manipulate the audio and video streams for this user) and sends back to the AS both the SDP returned by the MS and the Consumer response (9.). The AS extracts the Consumer response and takes note of both the MS instances it has been given and the connection-id information. It then completes the scenario by sending back to the UAC the SDP returned by the MS (11.). At this point, the UAC has successfully been attached to an MS. The AS only needs to set up a Control Channel to that MS, if needed. This step may not be required, especially if the Consumer request is an update to an existing session rather than the preparation of a new session. Assuming that a Control Channel towards that MS doesn't exist yet, the AS creates it as usual by sending an INVITE directly to the MS for which it has an address. Once done with that, it can start manipulating the audio and video streams of the UAC. To do so, it refers to the <connection-id> element as reported by the MRB, rather than relying on the <connection-id> element that it is aware of. In fact, the AS is aware of a connection-id value (fd4fush5:117652221, built out of the messages exchanged with the MRB), while the MS is aware of another (32pbdxZ8:KQw677BF, built out of the MRB-MS interaction). The right connection-id is of course the one the MS is aware of, and as such the AS refers to that connection-id, which the MRB added to the Consumer response just for that purpose.

Whereas in the Inline-aware mode the AS knows it is sending an INVITE to an MRB and not to an MS, and acts accordingly (using the multipart/mixed payload to query for an MS able to fulfill its requirements), in the Inline-Unaware MRB Mode (IUMM) the AS does not distinguish an MRB from an MS. This means that an MRB-unaware AS having access to an MRB talks to it as if it were a generic MEDIACTRL MS: i.e., the AS negotiates a Control Channel directly with the MRB and attaches its media dialogs there as well. Of course, since the MRB doesn't provide any MS functionality by itself, it must act as a Proxy/B2BUA between the AS and an MS for both the Control Channel dialog and the media dialogs. According to implementation or deployment choices, simple redirects could also be exploited for that purpose. The problem is that without any Consumer request being placed by the MRB-unaware AS the MRB can't rely on AS-originated directives to pick one MS rather than another. In fact, the MRB can't know what the AS is looking for. The MRB is then assumed to pick one according to its logic, which is implementation specific. presents a ladder diagram of a typical Consumer request in the Inline-unaware topology:

| | | 2. 100 (Trying) | | |<----------------------| | | |--+ Pick an MS | | | | and redirect | | |<-+ INVITE there | | | | | | 3. INVITE | | | (application/cfw from 1.) | | |-------------------------->| | | 4. 100 (Trying) | | |<--------------------------| | | |--+ Negotiate | | | | CFW Control | | |<-+ Channel | | 5. 200 OK | | | (application/cfw from MS) | | |<--------------------------| | | 6. ACK | | |-------------------------->| | | | | 7. 200 OK | | |(application/cfw from MS) | |<----------------------| | | 8. ACK | | |---------------------->| | | | | | | |<<############## TCP CONNECTION #################>>| | | | CFW SYNC | |++++++++++++++++++++++++++++++++++++++++++++++++++>| | | . . . . . . ]]> As can be seen in the diagram, in this topology the MRB basically acts as a 3PCC between the AS and the chosen MS. The same can be said with respect to attaching UAC media dialogs. The MRB remembers the MS it has chosen for the AS, and for every UAC media dialog the AS tries to attach to the MRB, it makes sure that it is somehow actually redirected to the MS. No content for the presented messages is provided in this section, as in the IUMM mode no Consumer transaction is involved. In this example, a simple Control Channel negotiation occurs where the MRB acts as an intermediary, that is, picking an MS for the AS according to some logic. In this case, in fact, the AS does not support the MRB specification and so just tries to set up a Control Channel according to its own logic. It is worth pointing out that the MRB may actually enforce its decision about the MS to grant to the AS in different ways. Specifically, the sentence "redirect the INVITE" that is used in does not necessarily mean that a SIP 302 message should be used for that purpose. A simple way to achieve this may be provisioning the unaware AS with different URIs, all actually transparently handled by the MRB itself; this would allow the MRB to simply map those URIs to different MS instances. The SIP 'Contact' header may also be used by the MRB in a reply to an INVITE coming from an AS to provide the actual URI on which the chosen MS might be reached. A motivation for such a discussion, and more details on this topic, are provided in .

It is worthwhile to briefly address how media dialogs would be managed whenever an MRB is involved in the following scenarios. In fact, the presence of an MRB may introduce an additional complexity compared to the quite straightforward 1:1 AS-MS topology.

Normally, especially in the Query and IAMM case, the MRB would only handle Consumer requests by an AS, and after that the AS and the MS picked by the MRB for a specific request would talk directly to each other by means of SIP. This is made possible by the fact that the AS gets the MS SIP URI in reply to its request. In this case, an AS can simply relay media dialogs associated with that session to the right MS to have them handled accordingly. Of course, in order for this to work it is assumed that the AS creates a Control Channel to a chosen MS before it has any requests to service. An example of such a scenario is presented in . Please note that this diagram and subsequent diagrams in this section are simplified with respect to the actual protocol interactions. For instance, the whole SIP transactions are not presented, and only the originating messages are presented in order to clarify the scenario in a simple way.

| | | | | | | | 2. Consumer response | | | |<---------------------------| | | | | | | | 3. COMEDIA negotiation to create CFW channel | | |-------------------------------------------------->| | | | | | |<<############## CFW CONNECTION #################>>| | 4. INVITE xyz | | | |--------------->| | | | | 5. Attach UAC to MS (3PCC) | | |-------------------------------------------------->| | | | | |<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>| | | | | . . . . . . . . ]]> As can be deduced from the diagram, the interactions among the components are quite straightforward. The AS knows which MS it has been assigned to (as a consequence of the MRB Consumer request, whether it has been achieved by means of HTTP or SIP), and so it can easily attach any UAC accessing its functionality to the MS itself and manipulate its media connections by using the CFW Control Channel as usual. In such a scenario, the MRB is only involved as a locator. Once the MRB provides the AS with the URI of the required resource, it doesn't interfere with subsequent interactions unless it wants to perform monitoring (e.g., by exploiting the Publishing information reported by the MS). As a consequence, the scenario basically becomes 1:1 between the AS and the MS again. Nevertheless, there are cases when having an MRB in the SIP signaling path as well might be a desired feature, e.g., for more control over the use of the resources. Considering how the Consumer interface has been envisaged, this feature is easily achievable, with no change to the protocol required at all. Specifically, in order to achieve such functionality, the MRB may reply to a Consumer request with a URI for which the MRB is responsible (rather than the MS SIP URI as discussed previously) and map this URI to the actual MS URI in its business logic; this would be transparent to the AS. This way, the AS would interact with the MRB as if it were the MS itself. shows how the scenario would change in this case.

| | | | | | | | 2. Consumer response | | | |<---------------------------| | | | | | | | 3. COMEDIA negotiation | | | |--------------------------->| | | | | 4. COMEDIA neg. | | | |--------------------->| | | | | | |<<############## CFW CONNECTION #################>>| | 5. INVITE xyz | | | |--------------->| | | | | 6. Attach UAC to MS (3PCC) | | | |--------------------------->| | | | | 7. Attach UAC (3PCC) | | | |--------------------->| | | | | |<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>| | | | | . . . . . . . . ]]> This time, even though the MRB has picked a specific MS after a request from an AS, it replies with another SIP URI, a URI it would reply to itself. The AS would contact that URI in order to negotiate the Control Channel, and the MRB would proxy/forward the request to the actual MS transparently. Eventually, the Control Channel would be instantiated between the AS and the MS. The same happens for UACs handled by the AS; the AS would forward the calls to the URI provided to it, the one handled by the MRB, which would in turn relay the call to the MS in order to have the proper RTP channels created between the UAC and the MS. This scenario is not very different from the previous scenario, except that the MRB is now on the signaling path for both the SIP control dialog and the SIP media dialogs, allowing it to have more control of the resources (e.g., triggering a BYE if a resource has expired). There are several possible approaches an MRB might take to allocate URIs to map to a requested MS. For example, an MRB might use SIP URI parameters to generate multiple SIP URIs that are unique but that all route to the same host and port, e.g., sip:MrbToMs@mrb.example.com:5080;p=1234567890. Alternatively, the MRB might simply allocate a pool of URIs for which it would be responsible and manage the associations with the requested MS services accordingly.

As mentioned previously, in the IUMM case the AS would interact with the MRB as if it were the MS itself. One might argue that this would make the AS act as it would in the IAMM case. This is not the case, however, since the AS actually provided the MRB with information about the resources it required, leading to the selection of a proper MS, while in the IUMM case the MRB would have to pick an MS with no help from the AS at all. That said, the IUMM case is also very interesting with respect to media dialog management. In fact, in the MRB-unaware mode, there would be no Consumer request, and an AS would actually see the MRB as an MS. Unlike the previous scenarios, because there is no AS<->MRB interaction and as such no MS selection process, the MRB would likely be in the signaling path anyway, at least when the AS first shows up. The MRB could either redirect the AS to an MS directly or transparently act as a Proxy/B2BUA and contact an MS (according to implementation-specific policies) on behalf of the unaware AS. While apparently not a problem, this raises an issue when the same unaware AS has several sessions with different MS. The AS would only see one "virtual" MS (the MRB), and so it would relay all calls there, making it hard for the MRB to understand where these media dialogs should belong: specifically, whether the UAC calling belongs to the AS application logic leading to MS1 or MS2, or somewhere else. One possible, and very simple, approach to take care of this issue is to always relay the SIP dialogs from the same unaware AS to the same MS, as depicted in .

| | | | | | 2. COMEDIA neg. (A) | | | | |--------------------->| | | | | | | | |<<############## CFW CONNECTION #################>>| | | | | | | | | 3. COMEDIA negotiation (B) | | | | |--------------------------->| | | | | | 4. COMEDIA neg. (B) | | | | |--------------------->| | | | | | | | |<<############## CFW CONNECTION #################>>| | 5. INVITE xyz | | | |--------------->| | | | | | 6. Attach UAC1 to MS (3PCC)| | | | |--------------------------->| | | | | | 7. Attach UAC (3PCC) | | | | |--------------------->| | | | | | |<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>| | | | | | | | 8. INVITE| | | | | jkl | | | | |--------->| | | | | | 9. Attach UAC2 to MS (3PCC)| | | | |--------------------------->| | | | | | 10. Attach UAC (3PCC)| | | | |--------------------->| | | | | | | |<<++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>| | | | | | . . . . . . . . . . ]]> In this example, the AS creates two different Control Channel sessions (A and B) to address two different business logic implementations; e.g., the AS SIP URI 'xyz' (associated with CFW session A) may be an IVR pizza-ordering application, while the AS SIP URI 'jkl' (associated with CFW session B) may be associated with a conference room. It's quite clear, then, that if the MRB forwarded the two CFW sessions to two different MS, the handling of UAC media dialogs would prove troublesome, because the MRB would have difficulty figuring out whether UAC1 should be attached to the MS managing CFW session A or the MS managing CFW session B. In this example, forwarding all CFW sessions and UAC media dialogs coming from the same MRB-unaware AS to the same MS would work as expected. The MRB would in fact leave the mapping of media dialogs and CFW sessions up to the AS. This approach, while very simple and indeed not very scalable, would actually help take care of the issue. In fact, no matter how many separate Control Channels the AS might have with the MRB/MS (in this example, Control Channel A would be mapped to application xyz and Control Channel B to application jkl), the termination point would still always be the same MS, which would consequently be the destination for all media dialogs as well. To overcome the scalability limitations of such an approach, at least in regard to the MRB being in the SIP signaling path for all calls, a different approach needs to be exploited. In fact, especially in the case of different applications handled by the same unaware AS, it makes sense to try to exploit different MS for that purpose and to correctly track media dialogs being forwarded accordingly. This means that the MRB must find a way to somehow redirect the unaware AS to different MS when it predicts or realizes that a different application logic is involved. To do so, the MRB might use different approaches. One approach would use redirection, e.g., by means of a SIP 302 message in reply to a Control Channel negotiation originated by an unaware AS. Such an approach is depicted in .

| | | | | | | | 2. 302 Moved (MS) | | | |<---------------------------| | | | | | | | 3. COMEDIA negotiation | | | |-------------------------------------------------->| | | | | | |<<############## CFW CONNECTION #################>>| | | | | | 4. INVITE xyz | | | |--------------->| | | | | 5. Attach UAC1 to MS (3PCC)| | | |-------------------------------------------------->| | | | | |<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>| | | | | . . . . . . . . ]]> With this approach, the MRB might redirect the AS to a specific MS whenever a new Control Channel is to be created, and as a consequence the AS would redirect the related calls there. This is similar to the first approach of the Query/IAMM case, with the difference that no Consumer request would be involved. The scenario would again fall back to a 1:1 topology between the AS and the MS, making the interactions quite simple. Just as before, the MRB might be interested in being in the signaling path for the SIP dialogs, instead of just acting as a locator. A third potential approach could be implementing the "virtual" URIs handled by the MRB, as described in the previous section. Rather than resorting to explicit redirection or always using the same MS, the MRB may redirect new SIP control dialogs to one of its own URIs, using the same approach previously presented in . Such an approach, as applied to the IUMM case, is depicted in .

| | | | | | | | 2. 302 Moved (MRB') | | | |<------------------------------| | | | | | | | 3. COMEDIA negotiation (MRB') | | | |------------------------------>| | | | | 4. COMEDIA neg. | | | |------------------> | | | | | |<<############## CFW CONNECTION #################>>| | | | | | 5. INVITE xyz | | | |--------------->| | | | | 6. Attach UAC1 to MRB' (3PCC) | | | |------------------------------>| | | | | 7 Attach UAC (3PCC) | | |------------------> | | | | |<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>| | | | | . . . . . . . . ]]> It is worth pointing out, though, that in both cases there are scenarios where there could be no assurance that the 302 sent by the MRB would be seen by the AS. In fact, should a proxy be between the AS and the MRB, such a proxy could itself act on the 302. To properly cope with such an issue, the MRB might also use the 'Contact' header in the SIP responses to the INVITE to address the right MS. Although the AS is not required to use the information in such a header to reach the MS, it could be reasonable to exploit it for that purpose, as it would take care of the proxy scenario mentioned above. To conclude, there is a further approach an MRB might try to exploit to take care of the IUMM case. Since, as explained before, the issues related to the IUMM case mostly relate to the fact that the MRB is seen as a single MS instance by the AS, a simple way to overcome this might be to make the MRB look like a set of different MS right away; this can be done by simply provisioning the unaware AS with a series of different URIs, all handled by the MRB itself acting as a pool of "virtual" MS. This way, the AS may be designed to use different MS for different classes of calls, e.g., for different applications it is managing (two in the example presented in this section), and as such would contact two different provisioned URIs to create two distinct Control Channels towards two different MS. Since both of the URIs would be handled by the MRB, the MRB can use them to determine to which MS each call should be directed. Expanding on by removing the constraint to always use the same MS, this new scenario might look like that depicted in .

| | | | | | | 2. COMEDIA (A) | | | | | |---------------->| | | | | | | | | | |<<############## CFW CONNECTION 1 ##########>>| | | | | | | | | | | 3. COMEDIA negotiation (B) | | | | | | INVITE fake-ms2 | | | | | |--------------------------->| | | | | | | 4. COMEDIA neg. (B) | | | | |--------------------->| | | | | | | | | |<<############## CFW CONNECTION 2 ###############>>| | | | | | | | 5. INVITE xyz | | | | |--------------->| | | | | | | 6. Attach UAC1 to fake-ms1 (3PCC) | | | | |--------------------------->| | | | | | | 7. Attach UAC | | | | | |---------------->| | | | | | | | |<<++++++++++++++++++++++ RTP channels +++++++++++++++++++++++>>| | | | | | | | | 8. INVITE jkl | | | | |--------------->| | | | | | | 9. Attach UAC2 to fake-ms2 (3PCC) | | | | |--------------------------->| | | | | | | 10. Attach UAC | | | | | |--------------------->| | | | | | | |<<+++++++++++++++++++++++++ RTP channels +++++++++++++++++++++++++>>| | | | | | | . . . . . . . . . . . . ]]> In this new example, we still assume that the same unaware AS is handling two different applications, still associated with the same URIs as before. This time, though, we also assume that the AS has been designed to try to use different MS instances to handle the two very different applications for which it is responsible. We also assume that it has been configured to be able to use two different MS instances, reachable at SIP URI 'fake-ms1' and 'fake-ms2', respectively, and both actually handled by the MRB transparently. This results, just as before, in two different Control Channels (A and B) being created, but this time towards two different MS. Specifically, the MRB makes sure that for this AS the Control Channel negotiation towards 'fake-ms1' is actually redirected to MS1. At the same time, 'fake-ms2' is associated with MS2. Once the AS has set up the Control Channels with both of the MS, it is ready to handle media dialogs. UAC1 calls the SIP URI 'xyz' on the AS to order a pizza. The AS attaches the media dialog to the MS it knows is responsible for that branch of application logic, i.e., 'fake-ms1'. The MRB in turn makes sure that it reaches the right MS instance, MS1. Later on, a different user, UAC2, calls SIP URI 'jkl' to join a conference room. This time, the AS attaches this new media dialog to the MS instance handling the conference application, i.e., 'fake-ms2'. Again, the MRB makes sure that it is actually MS2 that receives the dialog. Again, this diagram is only meant to describe how the MRB might enforce its decisions. Just as described in the previous examples, the MRB may choose to either act as a Proxy/B2BUA between the AS and the MS instances or redirect the AS to the right MS instances when they're first contacted (e.g., by means of the Contact header and/or a SIP redirect, as explained before) and let the AS attach the media dialogs by itself.

As shown in the previous diagrams, no matter what the topology, the AS and MS usually end up with a direct connection with respect to the CFW Control Channel. As such, it can be expected that the CFW protocol continue to work as it should, and as a consequence all the call flows presented in this document can easily be reproduced in those circumstances as well. Nevertheless, one aspect needs to be considered very carefully. It's worthwhile to remind readers that both the AS and the MS use some SIP-related information to address the entities they manipulate. This is the case, for instance, for the <connectionid> element to which both the AS and the MS refer when addressing a specific UAC. As explained in , this 'connectionid' identifier is constructed by concatenating the 'From' and 'To' tags extracted from a SIP header: specifically, from the headers of the AS<->MS leg that allows a UAC to be attached to the MS. The presence of an additional component in the path between the AS and the MS, the MRB, might alter these tags, thus causing the AS to use tags (AS<->MRB) different than those used by the MS (MRB<->MS). This would result in the AS and MS using different 'connectionid' identifiers to address the same UAC, thus preventing the protocol from working as expected. As a consequence, it's very important that any MRB implementation take very good care to preserve the integrity of the involved SIP headers when proxying/forwarding SIP dialogs between the AS and MS, in order not to "break" the behavior of the protocol. Let's take, for instance, the scenario depicted in , especially steps 6 and 7, which specifically address a UAC being attached by an AS to an MS via the MRB. Let's assume that shows what happens to the 'From' and 'To' headers in that scenario, when dealing with the 3PCC approach to attach a specific UAC to the MS.

| | | | | SIP [..] | | | | From: <..>;tag=a1b2c3 | | | | To: <..>;tag=d4e5f6 | | | |<------------------------>| | | | | SIP [..] | | | | From: <..>;tag=aaabbb | | | | To: <..>;tag=cccddd | | | |<---------------------->| | | | | | | 1. CONTROL (play announcement to UAC) | | |-------------------------------------------------->| | | 2. 200 (IVR Error!) | | |<--------------------------------------------------| | | | | . . . . . . . . ]]> In this example, once done with the 3PCC, and now that the UAC is attached to the MS, the AS and the MS end up with different interpretations of what the 'connectionid' for the UAC should be. In fact, the AS builds a 'connectionid' using the tags it is aware of (a1b2c3:d4e5f6), while the MS builds a different identifier after receiving different information from the MRB (aaabbb:cccddd). As a consequence, when the AS tries to play an announcement to the UAC using the connectionid it correctly constructed, the MS just as correctly replies with an error, since it doesn't know that identifier. This is correct protocol behavior, because in this case it was caused by misuse of the information needed for it to work as expected.

MS (CFW CONTROL, play) ------------------------------- CFW ffhg45dzf123 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 284 2. AS <- MS (CFW 200 OK) ------------------------ CFW ffhg45dzf123 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 148 ]]> In an even worse scenario, the connectionid might actually exist but might be mapped to a different UAC. In such a case, the transaction would succeed, but a completely different UAC would be involved, thus causing a silent failure that neither the AS nor the MS would be aware of. That said, proper management of these sensitive pieces of information by the MRB would prevent such failure scenarios from happening. How this issue is taken care of in the IAMM case (both CFW-based and media dialog-based) has already been described. Addressing this issue for the IUMM case is not documented in as explicitly out of scope and as such may be implementation specific. The same applies to SDP fields as well. In fact, the AS and MS use ad hoc SDP attributes to instantiate a Control Channel, as they use SDP labels to address specific media connections of a UAC media dialog when a fine-grained approach is needed. As a consequence, any MRB implementation should limit any SDP manipulation as much as possible or at least take very good care not to cause changes that could "break" the expected behavior of the CFW protocol.

All the MEDIACTRL documents have strong statements regarding security considerations within the context of the interactions occurring at all levels among the involved parties. Considering the sensitive nature of the interaction between AS and MS, particular efforts have been devoted to providing guidance on how to secure what flows through a Control Channel. In fact, transactions concerning dialogs, connections, and mixes are quite strongly related to resources actually being deployed and used in the MS. This means that it is in the interest of both AS and MS that resources created and handled by an entity are not manipulated by a potentially malicious third party if permission was not granted. Because strong statements are provided in the aforementioned documents and these documents provide good guidance to implementors with respect to these issues, this section will only provide the reader with some MEDIACTRL call flows that show how a single secured MS is assumed to reply to different AS when receiving requests that may cross the bounds within which each AS is constrained. This would be the case, for instance, for generic auditing requests, or explicit conference manipulation requests where the involved identifiers are not part of the context of the originating AS. To address a very specific scenario, let's assume that two different AS, AS1 and AS2, have established a Control Channel with the same MS. Considering the SYNC transaction that an AS and an MS use to set up a Control Channel, the MS is able to discern the requests coming from AS1 from the requests coming from AS2. In fact, as explained in Sections and , an AS and an MS negotiate a cfw-id attribute in the SDP, and the same value is subsequently used in the SYNC message on the Control Channel that is created after the negotiation, thus reassuring both the AS and the MS that the Control Channel they share is in fact the channel they negotiated in the first place. Let's also assume that AS1 has created a conference mix (confid=74b6d62) to which it has attached some participants within the context of its business logic, while AS2 has created a currently active IVR dialog (dialogid=dfg3252) with a user agent it is handling (237430727:a338e95f). AS2 has also joined two connections to each other (1:75d4dd0d and 1:b9e6a659). Clearly, it is highly desirable that AS1 not be aware of what AS2 is doing with the MS and vice versa, and that they not be allowed to manipulate each other's resources. The following transactions will occur: AS1 places a generic audit request to both the Mixer and IVR packages. AS2 places a generic audit request to both the Mixer and IVR packages. AS1 tries to terminate the dialog created by AS2 (6791fee). AS2 tries to join a user agent it handles (1:272e9c05) to the conference mix created by AS1 (74b6d62). A sequence diagram of the above-mentioned transactions is depicted in , which shows how the MS is assumed to reply in all cases, in order to avoid security issues:

>| | | A2. 200 OK | |<<++++++++++++++++++++++++++++++++++++++++++++++++++++++++| | | | | B1. CONTROL (Mixer audit) | |++++++++++++++++++++++++++++++++++++++++++++++++++++++++>>| | | B2. 200 OK | |<<++++++++++++++++++++++++++++++++++++++++++++++++++++++++| | | | | | C1. CONTROL (IVR audit) | | |++++++++++++++++++++++++++++++++>>| | | C2. 200 OK | | |<<++++++++++++++++++++++++++++++++| | | | | | D1. CONTROL (Mixer audit) | | |++++++++++++++++++++++++++++++++>>| | | D2. 200 OK | | |<<++++++++++++++++++++++++++++++++| | | | | E1. CONTROL (dialogterminate) | |++++++++++++++++++++++++++++++++++++++++++++++++++++++++>>| | | E2. 403 Forbidden | |<<++++++++++++++++++++++++++++++++++++++++++++++++++++++++| | | | | | F1. CONTROL (join UAC&conf[AS1]) | | |++++++++++++++++++++++++++++++++>>| | | F2. 403 Forbidden | | |<<++++++++++++++++++++++++++++++++| | | | . . . . . . ]]> The expected outcome of the transaction is that the MS partially "lies" to both AS1 and AS2 when replying to the audit requests (not all of the identifiers are reported, but only those identifiers with which each AS is directly involved), and the MS denies the requests for the unauthorized operations (403). Looking at each transaction separately: In the first transaction (A1), AS1 places a generic <audit> request to the IVR package. The request is generic, since no attributes are passed as part of the request, meaning that AS1 is interested in the MS capabilities as well as all of the dialogs that the MS is currently handling. As can be seen in the reply (A2), the MS only reports in the <auditresponse> the package capabilities, while the <dialogs> element is empty; this is because the only dialog the MS is handling has actually been created by AS2, which causes the MS not to report the related identifier (6791fee) to AS1. In fact, AS1 could use that identifier to manipulate the dialog, e.g., by tearing it down and thus causing the service to be interrupted without AS2's intervention. In the second transaction (B1), AS1 places an identical <audit> request to the Mixer package. The request is again generic, meaning that AS1 is interested in the package capabilities as well as all the mixers and connections that the package is handling at the moment. This time, the MS reports not only capabilities (B2) but information about mixers and connections as well. However, this information is not complete; in fact, only information about mixers and connections originated by AS1 is reported (mixer 74b6d62 and its participants), while the information originated by AS2 is omitted in the report. The motivation is the same as before. In the third and fourth transactions (C1 and D1), it's AS2 that places an <audit> request to both the IVR and Mixer packages. As with the previous transactions, the audit requests are generic. Looking at the replies (C2 and D2), it's obvious that the capabilities section is identical to the replies given to AS1. In fact, the MS has no reason to "lie" about what it can do. The <dialogs> and <mixers> sections are totally different. AS2 in fact receives information about its own IVR dialog (6791fee), which was omitted in the reply to AS1, while it only receives information about the only connection it created (1:75d4dd0d and 1:b9e6a659) without any details related to the mixers and connections originated by AS1. In the fifth transaction (E1), AS1, instead of just auditing the packages, tries to terminate (<dialogterminate>) the dialog created by AS2 (6791fee). Since the identifier has not been reported by the MS in the reply to the previous audit request, we assume that AS1 accessed it via a different out-of-band mechanism. This is assumed to be an unauthorized operation, because the above-mentioned dialog is outside the bounds of AS1; therefore, the MS, instead of handling the syntactically correct request, replies (E2) with a framework-level 403 message (Forbidden), leaving the dialog untouched. Similarly, in the sixth and last transaction (F1), AS2 tries to attach (<join>) one of the UACs it is handling to the conference mix created by AS1 (74b6d62). Just as in the previous transaction, the identifier is assumed to have been accessed by AS2 via some out-of-band mechanism, since the MS didn't report it in the reply to the previous audit request. While one of the identifiers (the UAC) is actually handled by AS2, the other (the conference mix) is not; therefore, as with the fifth transaction, this last transaction is regarded by the MS as outside the bounds of AS2. For the same reason as before, the MS replies (F2) with a framework-level 403 message (Forbidden), leaving the mix and the UAC unjoined.

MS (CFW CONTROL, audit IVR) -------------------------------------- CFW 140e0f763352 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 81 A2. AS1 <- MS (CFW 200, auditresponse) -------------------------------------- CFW 140e0f763352 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 1419 audio/x-wav video/mpeg audio/x-wav video/mpeg mdy ymd dmy dm t24 t12 gen crn ord 60s 1800s basic gsm h261 h263 h263-1998 h264 B1. AS1 -> MS (CFW CONTROL, audit mixer) ---------------------------------------- CFW 0216231b1f16 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 87 B2. AS1 <- MS (CFW 200, auditresponse) -------------------------------------- CFW 0216231b1f16 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 903 basic gsm h261 h263 h263-1998 h264

C1. AS2 -> MS (CFW CONTROL, audit IVR) -------------------------------------- CFW 0216231b1f16 CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 81 C2. AS2 <- MS (CFW 200, auditresponse) -------------------------------------- CFW 0216231b1f16 200 Timeout: 10 Content-Type: application/msc-ivr+xml Content-Length: 1502 audio/wav video/mpeg audio/wav video/mpeg mdy ymd dmy dm t24 t12 gen crn ord 60s 1800s basic gsm h261 h263 h263-1998 h264 D1. AS2 -> MS (CFW CONTROL, audit mixer) ---------------------------------------- CFW 515f007c5bd0 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 87 D2. AS2 <- MS (CFW 200, auditresponse) -------------------------------------- CFW 515f007c5bd0 200 Timeout: 10 Content-Type: application/msc-mixer+xml Content-Length: 548 basic gsm h261 h263 h263-1998 h264 E1. AS1 -> MS (CFW CONTROL, dialogterminate) -------------------------------------------- CFW 7fdcc2331bef CONTROL Control-Package: msc-ivr/1.0 Content-Type: application/msc-ivr+xml Content-Length: 127 E2. AS1 <- MS (CFW 403 Forbidden) --------------------------------- CFW 7fdcc2331bef 403 F1. AS2 -> MS (CFW CONTROL, join to conference) ----------------------------------------------- CFW 140e0f763352 CONTROL Control-Package: msc-mixer/1.0 Content-Type: application/msc-mixer+xml Content-Length: 117 F2. AS2 <- MS (CFW 403 Forbidden) --------------------------------- CFW 140e0f763352 403 ]]>

The authors would like to thank Dale Worley for the thorough review of the whole document and for contributing text to make the document easier to read.