]> Telchemy Incorporated

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Shanghai Research Institute of China Telecom Corporation Limited

No. 1835, South Pudong Road Shanghai 200122 China zhangyx@sttri.com.cn

Shanghai Research Institute of China Telecom Corporation Limited

No. 1835, South Pudong Road Shanghai 200122 China zhaojing@sttri.com.cn

Huawei

101 Software Avenue, Yuhua District Nanjing Jiangsu 210012 China sunseawq@huawei.com

Real-time Applications and Infrastructure Area Audio/Video Transport Working Group Real Time Control Protocol This document defines an RTP Control Protocol (RTCP) Extended Report (XR) Block that allows the reporting of burst and gap loss metrics for use in a range of RTP applications.

This document defines a new block type to augment those defined in for use in a range of RTP applications. The new block type supports the reporting of the proportion of packets lost by the network. The losses during loss bursts are reported, together with the number of bursts and additional data, allowing the calculation of statistical parameters (mean and variance) of the distribution of burst lengths. Some uses of these metrics depend on the availability of the metric "cumulative number of packets lost" from RTCP . This block provides information on transient IP problems. Burst/gap metrics are typically used in Cumulative reports; however, they also may be used in Interval reports. The burstiness of packet loss affects user experience, may influence any sender strategies to mitigate the problem, and may also have diagnostic value. The metric belongs to the class of transport-related end system metrics defined in . The definitions of "burst", "gap", "loss", and "discard" are consistent with definitions in . To accommodate the range of jitter buffer algorithms and packet discard logic that may be used by implementors, the method used to distinguish between bursts and gaps may be an equivalent method to that defined in . The method used should produce the same result as that defined in for conditions of burst packet loss but may produce different results for conditions of time-varying jitter.

The use of RTCP for reporting is defined in . defines an extensible structure for reporting by using an RTCP Extended Report (XR). This document defines a new Extended Report block for use with and .

The Performance Metrics Framework provides guidance on the definition and specification of performance metrics. The "Guidelines for Use of the RTP Monitoring Framework" provides guidelines for reporting block format using RTCP XR. The Metrics Block described in this document is in accordance with the guidelines in and .

These metrics are applicable to a range of RTP applications that contain jitter buffers and don't use stream repair means, e.g., Forward Error Correction (FEC) and/or retransmission .

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 RFC 2119. In addition, the following terms are defined: A packet shall be regarded as lost if it fails to arrive within an implementation-specific time window. A packet that arrives within this time window but is too early or late to be played out or thrown away before playout due to packet duplication or redundancy shall be regarded as discarded. A packet shall be classified as one of received (or OK), discarded, or lost. The metric "cumulative number of packets lost" defined in reports a count of packets lost from the media stream (single Synchronization Source (SSRC) within a single RTP session). Similarly, the metric "number of packets discarded" defined in reports a count of packets discarded from the media stream (single SSRC within single RTP session) arriving at the receiver. The post-repair Loss RLE metric, which is defined in , can be used to report the number of packets that are not recovered by any repair techniques that are in use. The terms "burst" and "gap" are used in a manner consistent with that of RTCP XR . RTCP XR views an RTP stream as being divided into bursts, which are periods when the loss rate is high enough to cause noticeable quality degradation (generally over 5 percent loss rate) and gaps, which are periods when lost packets are infrequent and hence quality is generally acceptable.

Metrics in this block report on burst/gap loss in the stream arriving at the RTP system. The measurement of these metrics is made at the receiving end of the RTP stream. Each instance of this Metrics Block refers by SSRC to a separate auxiliary Measurement Information Block , which describes the measurement periods in use (see RFC 6776, Section 4.2). This Metrics Block relies on the measurement period in the Measurement Information Block indicating the span of the report. Senders MUST send this block in the same compound RTCP packet as the Measurement Information Block. Receivers MUST verify that the measurement period is received in the same compound RTCP packet as this Metrics Block. If not, this Metrics Block MUST be discarded.

The structure of the Burst/Gap Loss Metrics Block is as follows.

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | BT=20 | I |C| resv. | Block Length = 5 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC of Source | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -+-+-+-+-+-+-+-+ | Threshold | Sum of Burst Durations (ms) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Packets Lost in Bursts | Total... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ...Packets Expected in Bursts | Number of Bursts | Sum of| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ...Squares of Burst Durations (ms-squared) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A Burst/Gap Loss Metrics Block is identified by the constant 20. This field is used to indicate whether the burst/gap loss metrics are Sampled, Interval, or Cumulative metrics: I=10: Interval Duration - the reported value applies to the most recent measurement interval duration between successive metrics reports. I=11: Cumulative Duration - the reported value applies to the accumulation period characteristic of cumulative measurements. I=01: Sampled Value - the reported value is a sampled instantaneous value. In this document, burst/gap loss metrics can only be measured over definite intervals and cannot be sampled. Also, the value I=00 is reserved for future use. Senders MUST NOT use the values I=00 or I=01. If a block is received with I=00 or I=01, the receiver MUST discard the block. The 'C' flag is used to indicate whether the loss/discard report is combined with the burst/gap loss report in the same compound RTCP packet. The value is set to '1' if the loss/discard report and the burst gap loss report are combined. Otherwise, the value is set to '0'. If the 'C' flag is set to '1' but the burst/gap discard was not sent, the receiver MUST discard the burst/gap loss. These bits are reserved. They MUST be set to zero by senders and ignored by receivers (see , Section 4.2). The length of this report block in 32-bit words, minus one. For the Burst/Gap Loss Metrics Block, the block length is equal to 5. The block MUST be discarded if the block length is set to a different value. As defined in Section 4.1 of . The Threshold is equivalent to Gmin in , i.e., the number of successive packets that must be received prior to and following a lost packet in order for this lost packet to be regarded as part of a gap. Note that the threshold is calculated in accordance with the Gmin Calculation defined in Section 4.7.2 of RFC 3611. The total duration of bursts of lost packets in the period of the report (Interval or Cumulative). The measured value is an unsigned value. If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFF MUST be reported. The total number of packets lost during loss bursts.The measured value is an unsigned value. If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFF MUST be reported. The total number of packets expected during loss bursts (that is, the sum of received packets and lost packets). The measured value is an unsigned value. If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFF MUST be reported. The number of bursts in the period of the report (Interval or Cumulative). The measured value is an unsigned value. If the measured value exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFF MUST be reported. The sum of the squares of burst durations (where individual burst durations are expressed in ms) in the period of the report (Interval or Cumulative). The units for this quantity are milliseconds-squared. The measured value is an unsigned value. If the measured value exceeds 0xFFFFFFFFD, the value 0xFFFFFFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFFFFF MUST be reported.

The metrics described here are intended to be used as described in this section, in conjunction with information from the Measurement Information Block and also with the metric "cumulative number of packets lost" provided in standard RTCP . These metrics provide information relevant to statistical parameters, including: the fraction of packets lost during bursts (i.e., Burst Loss Rate in ), which can be calculated using the metric "Packets Loss in Bursts" and the metric "Total Packets Expected in Bursts" provided in the Burst/Gap Loss Metrics Block. the fraction of packets lost during gaps (i.e., Gap Loss Rate in ), which can be calculated using the metric "Packets Loss in Bursts" and the metric "Total Packets Expected in Bursts" provided in the Burst/Gap Loss Metrics Block. burst duration mean , which can be calculated using the metric "Packets Loss in Bursts" and the metric "Total Packets Expected in Bursts" provided in the Burst/Gap Loss Metrics Block. burst duration variance , which can be calculated using the metric "Packets Loss in Bursts" and the metric "Total Packets Expected in Bursts" provided in the Burst/Gap Loss Metrics Block. The details on calculation of these parameters in the metrics are described in .

This Metrics Block is applicable to a broad range of RTP applications. Where the metric is used with a Voice-over-IP (VoIP) application and the stream repair means is not available, the following considerations apply. RTCP XR views a call as being divided into bursts, which are periods when the loss rate is high enough to cause noticeable call quality degradation (generally over 5 percent loss rate), and gaps, which are periods when lost packets are infrequent and hence call quality is generally acceptable. If Voice Activity Detection is used, the Burst and Gap Durations shall be determined as if silence packets had been sent, i.e., a period of silence in excess of Gmin packets will terminate a burst condition. The recommended value for the threshold Gmin in causes a burst during which the call quality is degraded to a similar extent as it would be during a typical Pulse Code Modulation (PCM) Severely Errored Second.

defines the use of the Session Description Protocol (SDP) for signaling the use of XR blocks. XR blocks MAY be used without prior signaling.

This section augments the SDP attribute "rtcp-xr" defined in by providing an additional value of "xr-format" to signal the use of the report block defined in this document. The ABNF syntax is below.

xr-format =/ xr-bgl-block xr-bgl-block = "burst-gap-loss"

When SDP is used in the offer/answer context, the SDP Offer/Answer usage defined in for unilateral "rtcp-xr" attribute parameters applies. For detailed usage of offer/answer for unilateral parameters, refer to Section 5.2 of .

New block types for RTCP XR are subject to IANA registration. For general guidelines on IANA considerations for RTCP XR, refer to .

This document assigns the block type value 20 in the IANA "RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry" to the "Burst/Gap Loss Metrics Block".

This document also registers a new parameter "burst-gap-loss" in the "RTP Control Protocol Extended Reports (RTCP XR) Session Description Protocol (SDP) Parameters Registry".

The contact information for the registrations is: Qin Wu (sunseawq@huawei.com) 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China

This block does not provide per-packet statistics, so the risk to confidentiality documented in Section 7, paragraph 3 of does not apply. However, the gaps indicated within this block could be used to detect the timing of other events on the path between the sender and receiver. For example, a competing multimedia stream might cause a loss burst for the duration of the stream, allowing the receiver of this block to know when the competing stream was active. This risk is not a significant threat since the only information leaked is the timing of the loss, not the cause. Besides this, it is believed that this proposed RTCP XR report block introduces no other new security considerations beyond those described in .

Geoff Hunt wrote the initial draft of this document.

The authors gratefully acknowledge reviews and feedback provided by Bruce Adams, Philip Arden, Amit Arora, Bob Biskner, Kevin Connor, Claus Dahm, Randy Ethier, Roni Even, Jim Frauenthal, Albert Higashi, Tom Hock, Shane Holthaus, Paul Jones, Rajesh Kumar, Keith Lantz, Mohamed Mostafa, Amy Pendleton, Colin Perkins, Mike Ramalho, Ravi Raviraj, Albrecht Schwarz, Tom Taylor, Hideaki Yamada, Adam Roach, Dan Romascanu, Chris Lonvick, Alfred C. Morton Jr., Pete Resnick, Ted Lemon, Stephen Farrell, Richard Barnes, and Benoit Claise.

Harvard University

1350 Mass. Ave.CambridgeMA 02138- +1 617 495 3864sob@harvard.edu

Generalkeyword In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. Authors who follow these guidelines should incorporate this phrase near the beginning of their document: 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 RFC 2119. Note that the force of these words is modified by the requirement level of the document in which they are used. This memorandum describes RTP, the real-time transport protocol. RTP provides end-to-end network transport functions suitable for applications transmitting real-time data, such as audio, video or simulation data, over multicast or unicast network services. RTP does not address resource reservation and does not guarantee quality-of- service for real-time services. The data transport is augmented by a control protocol (RTCP) to allow monitoring of the data delivery in a manner scalable to large multicast networks, and to provide minimal control and identification functionality. RTP and RTCP are designed to be independent of the underlying transport and network layers. The protocol supports the use of RTP-level translators and mixers. Most of the text in this memorandum is identical to RFC 1889 which it obsoletes. There are no changes in the packet formats on the wire, only changes to the rules and algorithms governing how the protocol is used. The biggest change is an enhancement to the scalable timer algorithm for calculating when to send RTCP packets in order to minimize transmission in excess of the intended rate when many participants join a session simultaneously. [STANDARDS-TRACK] This document defines the Extended Report (XR) packet type for the RTP Control Protocol (RTCP), and defines how the use of XR packets can be signaled by an application if it employs the Session Description Protocol (SDP). XR packets are composed of report blocks, and seven block types are defined here. The purpose of the extended reporting format is to convey information that supplements the six statistics that are contained in the report blocks used by RTCP's Sender Report (SR) and Receiver Report (RR) packets. Some applications, such as multicast inference of network characteristics (MINC) or voice over IP (VoIP) monitoring, require other and more detailed statistics. In addition to the block types defined here, additional block types may be defined in the future by adhering to the framework that this document provides. This memo defines the Session Description Protocol (SDP). SDP is intended for describing multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation. [STANDARDS-TRACK] This document defines a new report block type within the framework of RTP Control Protocol (RTCP) Extended Reports (XRs). One of the initial XR report block types is the Loss Run Length Encoding (RLE) Report Block. This report conveys information regarding the individual Real-time Transport Protocol (RTP) packet receipt and loss events experienced during the RTCP interval preceding the transmission of the report. The new report, which is referred to as the Post-repair Loss RLE report, carries information regarding the packets that remain lost after all loss-repair methods are applied. By comparing the RTP packet receipts/losses before and after the loss repair is completed, one can determine the effectiveness of the loss- repair methods in an aggregated fashion. This document also defines the signaling of the Post-repair Loss RLE report in the Session Description Protocol (SDP). [STANDARDS-TRACK] This document discusses architectural issues related to the extensibility of Internet protocols, with a focus on design considerations. It is intended to assist designers of both base protocols and extensions. Case studies are included. A companion document, RFC 4775 (BCP 125), discusses procedures relating to the extensibility of IETF protocols. This document is not an Internet Standards Track specification; it is published for informational purposes. This document defines an RTP Control Protocol(RTCP) Extended Report (XR) Block that allows the reporting of a simple discard count metric for use in a range of RTP applications. This document defines an RTP Control Protocol (RTCP) Source Description (SDES) item and an RTCP Extended Report (XR) block carrying parameters that identify and describe a measurement period to which one or more other RTCP XR blocks may refer. [STANDARDS-TRACK] This memo proposes an extensible Real-time Transport Protocol (RTP) monitoring framework for extending the RTP Control Protocol (RTCP) with a new RTCP Extended Reports (XR) block type to report new metrics regarding media transmission or reception quality. In this framework, a new XR block should contain a single metric or a small number of metrics relevant to a single parameter of interest or concern, rather than containing a number of metrics that attempt to provide full coverage of all those parameters of concern to a specific application. Applications may then "mix and match" to create a set of blocks that cover their set of concerns. Where possible, a specific block should be designed to be reusable across more than one application, for example, for all of voice, streaming audio, and video. This document is not an Internet Standards Track specification; it is published for informational purposes. This document describes a framework and a process for developing Performance Metrics of protocols and applications transported over IETF-specified protocols. These metrics can be used to characterize traffic on live networks and services. This memo documents an Internet Best Current Practice. This document specifies a payload format for generic Forward Error Correction (FEC) for media data encapsulated in RTP. It is based on the exclusive-or (parity) operation. The payload format described in this document allows end systems to apply protection using various protection lengths and levels, in addition to using various protection group sizes to adapt to different media and channel characteristics. It enables complete recovery of the protected packets or partial recovery of the critical parts of the payload depending on the packet loss situation. This scheme is completely compatible with non-FEC-capable hosts, so the receivers in a multicast group that do not implement FEC can still work by simply ignoring the protection data. This specification obsoletes RFC 2733 and RFC 3009. The FEC specified in this document is not backward compatible with RFC 2733 and RFC 3009. [STANDARDS-TRACK] RTP retransmission is an effective packet loss recovery technique for real-time applications with relaxed delay bounds. This document describes an RTP payload format for performing retransmissions. Retransmitted RTP packets are sent in a separate stream from the original RTP stream. It is assumed that feedback from receivers to senders is available. In particular, it is assumed that Real-time Transport Control Protocol (RTCP) feedback as defined in the extended RTP profile for RTCP-based feedback (denoted RTP/AVPF) is available in this memo. [STANDARDS-TRACK] This document defines three RTP Control Protocol (RTCP) Extended Report (XR) Blocks that allow the reporting of loss, duplication and discard summary statistics metrics in a range of RTP applications.

The six metrics defined in this document are described below using the template from Section 5.4.4 of RFC 6390. Threshold Metric Metric Name: Threshold in RTP Metric Description: The Threshold is equivalent to Gmin in , i.e., the number of successive RTP packets that must be received prior to and following a lost RTP packet in order for this lost RTP packet to be regarded as part of a gap. Method of Measurement or Calculation: See , Threshold definition. Units of Measurement: See , Threshold definition. Measurement Point(s) with Potential Measurement Domain: See , 1st paragraph. Measurement Timing: See , 2nd paragraph for measurement timing and for Interval Metric flag. Use and Applications: See . Reporting Model: See RFC 3611. Sum of Burst Durations Metric Metric Name: Sum of Burst Durations in RTP Metric Description: The total duration of bursts of lost RTP packets in the period of the report. Method of Measurement or Calculation: See , Sum of Burst Durations definition. Units of Measurement: See , Sum of Burst Durations definition. Measurement Point(s) with Potential Measurement Domain: See , 1st paragraph. Measurement Timing: See , 2nd paragraph for measurement timing and for Interval Metric flag. Use and Applications: See . Reporting Model: See RFC 3611. Packets Lost in Bursts Metric Metric Name: RTP Packets lost in bursts Metric Description: The total number of RTP packets lost during loss bursts. Method of Measurement or Calculation: See , Packets Lost in Bursts definition. Units of Measurement: See , Packets lost in bursts definition. Measurement Point(s) with Potential Measurement Domain: See , 1st paragraph. Measurement Timing: See , 2nd paragraph for measurement timing and for Interval Metric flag. Use and Applications: See . Reporting Model: See RFC 3611. Total Packets Expected in Bursts Metric Metric Name: Total RTP packets expected in bursts Metric Description: The total number of RTP packets expected during loss bursts (that is, the sum of received RTP packets and lost RTP packets). Method of Measurement or Calculation: See , Total packets expected in bursts definition. Units of Measurement: See , Total packets expected in bursts definition. Measurement Point(s) with Potential Measurement Domain: See , 1st paragraph. Measurement Timing: See , 2nd paragraph for measurement timing and for Interval Metric flag. Use and Applications: See . Reporting Model: See RFC 3611. Number of Bursts Metric Metric Name: Number of bursts in RTP Metric Description: The total duration of bursts of lost RTP packets in the period of the report. Method of Measurement or Calculation: See , Number of bursts definition. Units of Measurement: See , Number of bursts definition. Measurement Point(s) with Potential Measurement Domain: See , 1st paragraph. Measurement Timing: See , 2nd paragraph for measurement timing and for Interval Metric flag. Use and Applications: See . Reporting Model: See RFC 3611. Sum of Squares of Burst Durations Metric Metric Name: Sum of Squares of Burst Durations in RTP Metric Description: The sum of the squares of burst durations (where individual burst durations are expressed in ms) over in the period of the report. Method of Measurement or Calculation: See , Sum of Squares of Burst Durations definition. Units of Measurement: See , Sum of Squares of Burst Durations definition. Measurement Point(s) with Potential Measurement Domain: See , 1st paragraph. Measurement Timing: See , 2nd paragraph for measurement timing and for Interval Metric flag. Use and Applications: See . Reporting Model: See RFC 3611.