SIP URI Inter Operator Traffic Leg parameter
EricssonHirsalantie 11Jorvas02420Finlandchrister.holmberg@ericsson.comEricssonKistavagen 25Stockholm16480Swedenjan.holm@ericsson.comDeutsche TelekomHeinrich-Hertz-Strasse 3-7Darmstadt64307Germany+4961515812766r.jesske@telekom.deATT718 Clairmore Ave08734Lanoka HarborUSAmd3135@att.com
RAI
In telecommunication networks, the signalling path between a calling user and a called user can be
partioned into segments, referred to as traffic legs. Each traffic leg may span networks belonging to
different operators, and will have its own characteristics that can be different from other traffic legs
in the same call. The directionality in traffic legs relates to a SIP request creating a dialogue and
stand-alone SIP request. A traffic leg might be associated with multiple SIP dialogs, e.g. in case a
B2BUA which modifies the SIP dialog identifier is located within the traffic leg.
This document defines a new SIP URI parameter, 'iotl', which can be used in a SIP URI to indicate
that the entity associated with the address, or an entity responsible for the host part of the address,
represents the end of a specific traffic leg (or multiple traffic legs).
The 'iotl' parameter is defined in order to fulfil requirements from the 3rd-Generation Partnership
Project (3GPP), but it can also be used in other network environments.
In a telecommunication network, an end user can be attached (e.g. using a radio access network)
to its own operator network (home network), or to another operator's network (visited network).
In the latter case the user is referred to as a roaming user.
Telecommunication operator networks are often not connected directly to each other.
Instead, there might be intermediate networks, referred to as transit networks, between
them. A transit network might act on a SIP level or on IP level.
In telecommunication networks, the signalling path between a calling user and a called user can be
partioned into segments, referred to as traffic legs. Each traffic leg may span networks belonging to
different operators, and will have its own characteristics that can be different from other traffic legs
in the same call. The directionality in traffic legs relates to a SIP request creating a dialogue and
stand-alone SIP request. A traffic leg might be associated with multiple SIP dialogs, e.g. in case a
B2BUA which modifies the SIP dialog identifier is located within the traffic leg.
The traffic leg information can be used by intermediary entities to make policy decisions, related
to e.g. media anchoring, signalling policy, insertion of media functions (e.g. transcoder) and charging.
The figure below shows two users (Alice and Bob) and the different type of networks that the
signaling might traverse. The signalling path can be divided into multiple traffic legs, and the type
of traffic legs depends on how the signalling is routed.
ORIG HNW = Originating Home NetworkTERM HNW = Terminating Home NetworkORIG VNW = Originating Visited NetworkTERM VNW = Terminating Visited Network
In Figure 1 Alice is a user initiating communication with Bob, and:
Alice is attached to an originating network, which is either the
home network of Alice, or a visited network (in case Alice is roaming). In both
cases any originating service is provided by the home network of Alice.
Bob is attached to a terminating network, which is either the home network
of Bob, or a visited network (in case Bob is roaming). In both cases any
terminating service is provided by the home network of Bob.
A transit network, providing transit functions (e.g. translation of free
phone numbers), may be included between the originating and terminating
networks and between visited and home networks.
This document defines a new SIP URI parameter , 'iotl', which can be used in a SIP URI to indicate that the entity
associated with the address, or an entity responsible for the host part of the address,
represents the end of a specific traffic leg (or multiple traffic legs).
The 'iotl' parameter is defined in order to fulfil requirements from the
3rd-Generation Partnership Project (3GPP), but it can also be used in other network environments.
This section describes examples of different types of traffic legs in 3GPP networks.
In this case, Alice is located in a visited network. When Alice sends the initial SIP INVITE
request for a call, one traffic leg (referred to as the 'visitedA-homeA' traffic leg)
represents the signalling path between the UA of Alice and the home S-CSCF of Alice.
In this case, Bob is located in a visited network. When the home S-CSCF of Bob forwards
the initial SIP INVITE request for a call towards Bob, one traffic leg
(referred to as the 'homeB-visitedB' traffic leg) represents the signalling path between
the home S-CSCF of Bob and the UA of Bob.
In this case, the home S-CSCF of Alice forwards the initial SIP INVITE request towards
the home S-CSCF of Bob. The signalling path between the S-CSCFs represents
one traffic leg (referred to as the 'homeA-homeB' traffic leg).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in .
As specified in , when a SIP entity
inserts a SIP URI in an initial request for a dialog, or in a stand-alone request, the SIP URI
will be used to route the request to another SIP entity, addressed by the SIP URI, or to a SIP entity
responsible for the host part of the SIP URI (e.g. a SIP registrar). If such entity represents
the end of one or more traffic legs, the SIP entity inserting the SIP URI can add a SIP URI 'iotl' parameter
to the SIP URI, to indicate the type(s) of traffic leg. Each parameter value indicates a type of
traffic leg.
For routing of a SIP request, a SIP entity can add the 'iotl' parameter to the SIP URI of
the Request-URI , or to the SIP URI
of a Route header field , of an
initial request for a dialog, or of an stand-alone request.
If, within an initial request for a dialog, or within a stand-alone request, multiple Route
header fields contain a SIP URI with a 'iotl' parameter, the 'iotl' parameter associated with
the SIP URI of the topmost Route header field (or, if the SIP URI of the topmost Route header
field does not contain an 'iotl' parameter, the SIP URI of the Route header field closest to
the topmost) identifies the type of traffic leg.
If a SIP request contains an 'iotl' parameter both in the Request-URI SIP URI, and in one or
more SIP-URIs of the Route header fields, the 'iotl' parameter associated with
the SIP URI of the topmost Route header field (or, if the SIP URI of the topmost Route header
field does not contain an 'iotl' parameter, the SIP URI of the Route header field closest to
the topmost) identifies the type of traffic leg.
If a SIP request contains an 'iotl' parameter only in the Request-URI SIP URI, the 'iotl'
parameter identifies the type of traffic leg.
During SIP registration , entities
can add the 'iotl' parameter to the SIP URI of a Path or Service-Route header field, if the
entity is aware that SIP URI will be used to indicate the end of a specific traffic leg for
initial requests for dialogs, or stand-alone requests, sent on the registration path.
An entity that understands the 'iotl' parameter MUST NOT, from a SIP request, remove 'iotl'
parameters from SIP URIs associated with other entities, unless the entity has means to
determine that the 'iotl' parameter does not represent a valid traffic leg.
This document does not specify the usage of the 'iotl' parameter within a SIP URI of a
Record-Route header field .
This section describes the SIP URI 'iotl' parameter values defined in this specification.
This value indicates that a SIP entity responsible for the host part of the SIP URI
associated with the parameter represents the end of a traffic leg between
the home network (originating) of the calling user and the home network (terminating)
of the called user.
In 3GPP, this traffic leg is between two S-CSCFs.
This value indicates that the SIP entity addressed by the SIP URI associated with the
parameter represents the end of a traffic leg between the home network (terminating)
of the called user and the visited network (terminating) in which the called user is
located.
In 3GPP, this traffic leg is between the home S-CSCF and the UE of the called user,
or between the Service Centralization and Continuity Application Server (SCC AS) in
the home network of the called user and Access Transfer Control Function (ATCF) in
the visited network of the called user.
This value indicates that a SIP entity responsible for the host part of the SIP URI
associated with the parameter represents the end of a traffic leg between
the visited network (originating) in which the calling user is located
and the home network (originating) of the calling user.
In 3GPP, this traffic leg is between the UE and the home S-CSCF of the calling user, or
between the P-CSCF in the visited network, serving the calling user, and the home S-CSCF
of the calling user.
This value indicates that the SIP entity addressed by the SIP URI associated with the
parameter represents the end of a traffic leg between the home network (originating)
and the visited network (originating) in which the calling user is located.
In 3GPP, this traffic leg is between the home S-CSCF of the calling user and the
Transit and Roaming Function (TRF) [3GPP TS 24.229]
serving the calling user, and exists in scenarios where the home S-CSCF of the calling user
forwards a request back to the visited network where the UE of the calling user is located.
An example of this is when the Roaming Architecture for Voice over IMS with Local breakout
(RAVEL) [3GPP TS 24.229] feature is enabled.
This value indicates that a SIP entity responsible for the host part of the SIP URI
associated with the parameter represents represents the end of a traffic leg between
the visited network (originating) of the calling user and the home
network (terminating) of the called user.
In 3GPP, this traffic leg is between the Transit and Roaming Function (TRF)
[3GPP TS 24.229] serving the calling user and the home S-CSCF of the called user, and
exists in scenarios where a request is forwarded from the visited network where the calling
user is located directly to the home S-CSCF of the called user. An example of this is when
the Roaming Architecture for Voice over IMS with Local breakout (RAVEL) [3GPP TS 24.229]
feature is enabled.
This section defines the ABNF for the 'iotl' SIP URI parameter.
The ABNF defined in this specification is conformant to RFC 5234
.
The ABNF
grammar for the role SIP URI parameter is:
There SHOULD exis a trust relationship between the networks that provide the
roaming role and the networks that use the information for making policy
decisions based on the role. In addition, there MUST exist an agreement
between the operators for usage of the roaming role information.
[RFC EDITOR NOTE: Please replace RFC-XXXX with the RFC number of this document.]
This specification adds one new value to the IANA registration in
the "SIP/SIPS URI Parameters" registry as defined in
.
The authors wish to thank everyone in the 3GPP community that gave comments
on the initial version of this document.
[RFC EDITOR NOTE: Please remove this section when publishing]draft-holmberg-dispatch-iotl-00
Added text on how to identify the traffic leg type when SIP-URIs of multiple
Route header fields and/or the Request-URI contain an 'iotl' parameter.Clarify that a traffic leg might span over multiple SIP dialogs.Added text saying that entities supporting the 'iotl' parameter must
not remove a parameter from a request, if the parameter is associated with
a SIP URI beloning to another entity.Modified ABNF, in order to allow multiple iotl values for a single URI.In IANA section, changed indication that predefined values exist.Example call flows added.
This section contains example call flows based on 3GPP usage of the SIP URI
'iotl' parameter.
The Visited Proxy (P-CSCF) adds the iotl value 'homeB-visitedB' to the Path header field
of the REGISTER request, to be used for terminating routing towards Alice. The Home Proxy (S-CSCF)
adds the iotl value 'visitedA-homeA' to the Service-Route header field, to be used for
originating initial/stand-alone requests from Alice.
| REGISTER F2 | | |
| |--------------->| REGISTER F3 | |
| | |--------------->| REGISTER F4 |
| | | |--------------->|
| | | | |
| | | | 200 (OK) F5 |
| | | |<---------------|
| | | 200 (OK) F6 | |
| | |<---------------| |
| | 200 (OK) F7 | | |
| |<---------------| | |
| 200 (OK) F8 | | | |
|<---------------| | | |
F1 REGISTER Alice -> P-CSCF
REGISTER sip:registrar.home1.net SIP/2.0
F2 REGISTER P-CSCF -> IBCF-V
REGISTER sip:registrar.home1.net SIP/2.0
Path:
F3 REGISTER IBCF-V -> IBCF-H
REGISTER sip:registrar.home1.net SIP/2.0
Path:
F4 REGISTER IBCF-H -> S-CSCF
REGISTER sip:registrar.home1.net SIP/2.0
Path:
F5 200 OK S-CSCF -> IBCF-H
200 OK
Path:
Service-Route:
F6 200 OK IBCF-H -> IBCF-V
200 OK
Path:
Service-Route:
F7 200 OK IBCF-V -> P-CSCF
200 OK
Path:
Service-Route:
F8 200 OK P-CSCF -> Alice
200 OK
Path:
Service-Route:
]]>
In the originating INVITE request from Alice, the iotl value 'visitedA-homeA',
received in the Service-Route header field during registration, is
added to the Route header field representing the Home Proxy S-CSCF, to indicate
the traffic leg type between the Visited Proxy P-CSCF and the Home Proxy S-CSCF.
| INVITE F2 | | |
| |--------------->| INVITE F3 | |
| | |--------------->| INVITE F4 |
| | | |--------------->|
| | | | |
| | | | 180 F5 |
| | | 180 F6 |<---------------|
| | 180 F7 |<---------------| |
| 180 F8 |<---------------| | |
|<---------------| | | |
| | | | |
F1 INVITE Alice -> P-CSCF
INVITE sip:Bob@homeB.net SIP/2.0
Route: ,
F2 INVITE P-CSCF -> IBCF-V
INVITE sip:Bob@homeB.net SIP/2.0
Route: ,
F3 INVITE IBCF-V -> IBCF-H
INVITE sip:Bob@homeB.net SIP/2.0
Route: ,
F4 INVITE IBCF-H -> S-CSCF
INVITE sip:Bob@homeB.net SIP/2.0
Route:
]]>
In the terminating INVITE request towards Alice, the iotl value 'homeB-visitedB',
provided to the Home Proxy S-CSCF during registration, is
added to the Route header field representing the Visited Proxy P-CSCF, to indicate
the traffic leg type between the Home Proxy S-CSCF and the Visited Proxy P-CSCF.
| INVITE F2 | | |
| |--------------->| INVITE F3 | |
| | |--------------->| INVITE F4 |
| | | |--------------->|
| | | | |
| | | | 180 F5 |
| | | 180 F6 |<---------------|
| | 180 F7 |<---------------| |
| 180 F8 |<---------------| | |
|<---------------| | | |
| | | | |
F1 INVITE S-CSCF -> IBCF-H
INVITE sip:Bob@visitedB.net SIP/2.0
Route: , IBCF-V
INVITE sip:Bob@visitedB.net SIP/2.0
Route: , P-CSCF
INVITE sip:Bob@visitedB.net SIP/2.0
Route: Bob
INVITE sip:Bob@visitedB.net SIP/2.0
]]>
The S-CSCF of the originating home network adds the iotl value 'homeA-homeB'
in the Request-URI of the INVITE, sent towards the S-CSCF of the terminating
network, to indicate the traffic leg type between the S-CSCFs.
| INVITE F2 | | |
| |--------------->| INVITE F3 | |
| | |--------------->| INVITE F4 |
| | | |--------------->|
| | | | |
| | | | 180 F5 |
| | | 180 F6 |<---------------|
| | 180 F7 |<---------------| |
| 180 F8 |<---------------| | |
|<---------------| | | |
| | | | |
F1 INVITE S-CSCF-A -> IBCF-A
INVITE sip:Bob@visitedB.net;iotl=homeA-homeB SIP/2.0
F2 INVITE IBCF-a -> IBCF-B
INVITE sip:Bob@visitedB.net;iotl=homeA-homeB SIP/2.0
F3 INVITE IBCF-B -> I-CSCF-B
INVITE sip:Bob@visitedB.net;iotl=homeA-homeB SIP/2.0
F4 INVITE I-CSCF-B -> S-CSCF-B
INVITE sip:Bob@visitedB.net;iotl=homeA-homeB SIP/2.0
]]>