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Internet Engineering Task Force (IETF) J. OttRequest for Comments: 7097 V. Singh, Ed.Category: Standards Track Aalto UniversityISSN: 2070-1721 I. Curcio Nokia Research Center January 2014RTP Control Protocol (RTCP) Extended Report (XR)for RLE of Discarded PacketsAbstract The RTP Control Protocol (RTCP) is used in conjunction with the Real- time Transport Protocol (RTP) in order to provide a variety of short- term and long-term reception statistics. The available reporting may include aggregate information across longer periods of time as well as individual packet reporting. This document specifies a per-packet report metric capturing individual packets discarded from the de- jitter buffer after successful reception.Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available inSection 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7097.Ott, et al. Standards Track [Page 1]

RFC 7097 RTCP XR Discard RLE January 2014Copyright Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject toBCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.Table of Contents1. Introduction ....................................................32. Terminology .....................................................43. RTCP XR Discard RLE Report Block ................................44. Protocol Operation ..............................................64.1. Reporting Node (Receiver) ..................................64.2. Media Sender ...............................................65. SDP Signaling ...................................................66. Security Considerations .........................................77. IANA Considerations .............................................77.1. XR Report Block Registration ...............................77.2. SDP Parameter Registration .................................87.3. Contact Information for IANA Registrations .................88. Acknowledgments .................................................89. References ......................................................89.1. Normative References .......................................89.2. Informative References .....................................9Appendix A. Metrics Represented Using the Template fromRFC 6390 ..10Ott, et al. Standards Track [Page 2]

RFC 7097                   RTCP XR Discard RLE              January 20141.  Introduction   RTP [RFC3550] provides a transport for real-time media flows such as   audio and video together with the RTP Control Protocol (RTCP), which   provides periodic feedback about the media streams received in a   specific duration.  In addition, RTCP can be used for timely feedback   about individual events to report (e.g., packet loss) [RFC4585].   Both long-term and short-term feedback enable a media sender to adapt   its media transmission and/or encoding dynamically to the observed   path characteristics.RFC 3611 [RFC3611] defines RTCP Extended Reports as a detailed   reporting framework to provide more than just the coarse Receiver   Report (RR) statistics.  The detailed reporting may enable a media   sender to react more appropriately to the observed networking   conditions as these can be characterized better, although at the   expense of extra overhead.   Among many other report blocks,RFC 3611 specifies the Loss Run   Length Encoding (RLE) block, which reports runs of packets received   and lost with the granularity of individual packets.  This can help   both error recovery and path loss characterization.  In addition to   lost packets,RFC 3611 defines the notion of "discarded" packets:   packets that were received but dropped from the de-jitter buffer   because they were either too early (for buffering) or too late (for   playout).  The "discard rate" metric is part of the Voice over IP   (VoIP) metrics report block even though it is not just applicable to   audio: it is specified as the fraction of discarded packets since the   beginning of the session (seeSection 4.7.1 of RFC 3611 [RFC3611]).   The discard metric is believed to be applicable to a large class of   RTP applications that use a de-jitter buffer [RFC5481].   Recently proposed extensions to the Extended Reports (XRs) reporting   suggest enhancing this discard metric:   o  Reporting the number of discarded packets in a measurement      interval, i.e., either during the last reporting interval or since      the beginning of the session, as indicated by a flag in the      suggested XR [RFC7002].  If an endpoint needs to report packet      discard due to reasons other than early and late arrival (for      example, discard due to duplication, redundancy, etc.), then it      should consider using the Discarded Packets report block      [RFC7002].   o  Reporting gaps and bursts of discarded packets during a      measurement interval, i.e., the last reporting interval or the      duration of the session [RFC7003].Ott, et al.                  Standards Track                    [Page 3]

RFC 7097 RTCP XR Discard RLE January 2014 o Reporting the sum of payload bytes discarded during a measurement interval, i.e., the last reporting interval or the duration of the session [DISCARD-METRIC]. However, none of these metrics allow a receiver to report precisely which packets were discarded. While this information could in theory be derived from high-frequency reporting on the number of discarded packets [RFC7002] or from the gap/burst report [RFC7003], these two mechanisms do not appear feasible: the former would require an unduly high amount of reporting, which still might not be sufficient due to the non-deterministic scheduling of RTCP packets. The latter incurs significant complexity and reporting overhead and might still not deliver the desired accuracy. This document defines a discard report block following the idea of the run-length encoding applied for lost and received packets in [RFC3611].2. Terminology 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 inBCP 14,RFC 2119 [RFC2119]. The terminology defined in RTP [RFC3550] and in the extensions for XR reporting [RFC3611] applies.3. RTCP XR Discard RLE Report Block The RTCP XR Discard RLE report block uses the same format as specified for the loss and duplicate report blocks inRFC 3611 [RFC3611]. Figure 1 describes the packet format. The fields "BT", "T", "block length", "SSRC of source", "begin_seq", and "end_seq" have the same semantics and representation as defined in [RFC3611], with the addition of the "E" flag to indicate the reason for discard. The "chunks" encoding the run length have the same representation as inRFC 3611, but encode discarded packets. A definition of a discarded packet is given inRFC 7002 [RFC7002].Ott, et al. Standards Track [Page 4]

RFC 7097                   RTCP XR Discard RLE              January 2014       0               1               2               3       0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |     BT=25     |rsvd |E|   T   |         block length          |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                        SSRC of source                         |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |          begin_seq            |             end_seq           |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |          chunk 1              |             chunk 2           |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      :                              ...                              :      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |          chunk n-1            |             chunk n           |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                Figure 1: RTCP XR Discard RLE Report Block   Block Type (BT, 8 bits): A Discard RLE report block is identified by   the constant 25.   rsvd (3 bits): This field is reserved for future definition.  In the   absence of such definition, the bits in this field MUST be set to   zero and MUST be ignored by the receiver.   The 'E' bit is introduced to distinguish between packets discarded   due to early arrival and those discarded due to late arrival.  The   'E' bit is set to '1' if the chunks represent packets discarded due   to arriving too early and is set to '0' otherwise.   In case both early and late discarded packets shall be reported, two   Discard RLE report blocks MUST be included; their sequence number   range MAY overlap, but individual packets MUST only be reported as   either early or late and not appear marked in both.  If packets   appear in both report blocks, the conflicting packets will be   ignored.  Packets not reported in either block are considered to be   properly received and not discarded.   Discard RLE report blocks SHOULD be sent in conjunction with an RTCP   RR as a compound RTCP packet.Ott, et al.                  Standards Track                    [Page 5]

RFC 7097 RTCP XR Discard RLE January 20144. Protocol Operation This section describes the behavior of the reporting node (= media receiver) and the media sender.4.1. Reporting Node (Receiver) Transmission of RTCP XR Discard RLE report blocks is up to the discretion of the media receiver, as is the reporting granularity. However, it is RECOMMENDED that the media receiver signal all discarded packets using the method defined in this document. If all packets over a reporting period are discarded, the media receiver MAY use the Discard Report Block [RFC7002] instead. In case of limited available reporting bandwidth, it is up to the receiver whether or not to include RTCP XR Discard RLE report blocks. The media receiver MAY send the Discard RLE report blocks as part of the regularly scheduled RTCP packets, as perRFC 3550. It MAY also include Discard RLE report blocks in immediate or early feedback packets, as perRFC 4585.4.2. Media Sender The media sender MUST be prepared to operate without receiving any Discard RLE report blocks. If Discard RLE report blocks are generated by the media receiver, the media sender cannot rely on all these reports being received, nor can the media sender rely on a regular generation pattern from the media receiver. However, if the media sender receives RTCP XR reports but the reports contain no Discard RLE report blocks and is aware that the media receiver supports Discard RLE report blocks, it MAY assume that no packets were discarded at the media receiver.5. SDP Signaling A participant of a media session MAY use SDP to signal its support for the report block specified in this document or use them without any prior signaling (seeSection 5 of RFC 3611 [RFC3611]). For signaling in SDP, the RTCP XR attribute as defined inRFC 3611 [RFC3611] MUST be used. The SDP [RFC4566] attribute 'xr-format' defined inRFC 3611 is augmented as described in the following to indicate the discard RLE metric.Ott, et al. Standards Track [Page 6]

RFC 7097                   RTCP XR Discard RLE              January 2014      rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)]                       CRLF   ; defined in [RFC3611]      xr-format      =/ xr-discard-rle      xr-discard-rle = "discard-rle"   The parameter 'discard-rle' is used to indicate support for the   Discard RLE report block defined inSection 3.   When SDP is used in Offer/Answer context, the mechanism defined inRFC 3611 [RFC3611] for unilateral "rtcp-xr" attribute parameters   applies (seeSection 5.2 of RFC 3611 [RFC3611]).6.  Security Considerations   The Discard RLE report block provides per-packet statistics so the   risk to confidentiality documented inSection 7, Paragraph 3, ofRFC3611 [RFC3611] applies.  In some situations, returning very detailed   error information (e.g., over-range measurement or measurement   unavailable) using this report block can provide an attacker with   insight into the security processing.  Implementers should consider   the guidance in [NO-SRTP] for using appropriate security mechanisms,   i.e., where security is a concern, the implementation should apply   encryption and authentication to the report block.  For example, this   can be achieved by using the AVPF profile together with the Secure   RTP profile as defined inRFC 3711 [RFC3711]; an appropriate   combination of the two profiles (an "SAVPF") is specified inRFC 5124   [RFC5124].  However, other mechanisms also exist [SRTP-OPTIONS] and   might be more suitable.   Additionally, The security considerations ofRFC 3550 [RFC3550],RFC3611 [RFC3611], andRFC 4585 [RFC4585] apply.7.  IANA Considerations   New block types for RTCP XR are subject to IANA registration.  For   general guidelines on IANA considerations for RTCP XR, refer toRFC3611.7.1.  XR Report Block Registration   This document extends the IANA "RTP Control Protocol Extended Reports   (RTCP XR) Block Type Registry" by assigning value 25 to DRLE (Discard   RLE Report).Ott, et al.                  Standards Track                    [Page 7]

RFC 7097                   RTCP XR Discard RLE              January 20147.2.  SDP Parameter Registration   This document registers 'discard-rle' in the "RTCP XR SDP   Parameters".7.3.  Contact Information for IANA Registrations   Joerg Ott (jo@comnet.tkk.fi)   Aalto University Comnet, Otakaari 5A, 02150 Espoo, Finland.8.  Acknowledgments   The authors would like to thank Alan Clark, Roni Even, Sam Hartman,   Colin Perkins, Dan Romascanu, Dan Wing, and Qin Wu for providing   valuable feedback on earlier draft versions of this document.9.  References9.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.              Jacobson, "RTP: A Transport Protocol for Real-Time              Applications", STD 64,RFC 3550, July 2003.   [RFC3611]  Friedman, T., Caceres, R., and A. Clark, "RTP Control              Protocol Extended Reports (RTCP XR)",RFC 3611, November              2003.   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,              "Extended RTP Profile for Real-time Transport Control              Protocol (RTCP)-Based Feedback (RTP/AVPF)",RFC 4585, July              2006.   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session              Description Protocol",RFC 4566, July 2006.   [RFC7002]  Clark, A., Zorn, G., and Q. Wu, "RTP Control Protocol              (RTCP) Extended Report (XR) Block for Discard Count Metric              Reporting",RFC 7002, September 2013.Ott, et al.                  Standards Track                    [Page 8]

RFC 7097                   RTCP XR Discard RLE              January 20149.2.  Informative References   [RFC7003]  Clark, A., Huang, R., and Q. Wu, "RTP Control Protocol              (RTCP) Extended Report (XR) Block for Burst/Gap Discard              Metric Reporting",RFC 7003, September 2013.   [RFC5481]  Morton, A. and B. Claise, "Packet Delay Variation              Applicability Statement",RFC 5481, March 2009.   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.              Norrman, "The Secure Real-time Transport Protocol (SRTP)",RFC 3711, March 2004.   [RFC5124]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for              Real-time Transport Control Protocol (RTCP)-Based Feedback              (RTP/SAVPF)",RFC 5124, February 2008.   [NO-SRTP]  Perkins, C. and M. Westerlund, "Securing the RTP Protocol              Framework: Why RTP Does Not Mandate a Single Media              Security Solution", Work in Progress, October 2013.   [SRTP-OPTIONS]              Westerlund, M. and C. Perkins, "Options for Securing RTP              Sessions", Work in Progress, November 2013.   [DISCARD-METRIC]              Singh, V., Ed., Ott, J., and I. Curcio, "RTP Control              Protocol (RTCP) Extended Report (XR) for Bytes Discarded              Metric", Work in Progress, November 2013.Ott, et al.                  Standards Track                    [Page 9]

RFC 7097                   RTCP XR Discard RLE              January 2014Appendix A.  Metrics Represented Using the Template fromRFC 6390   a.  RLE of Discarded RTP Packets Metric       *  Metric Name: RLE - Run-length encoding of Discarded RTP          Packets Metric.       *  Metric Description: Instances of RTP packets discarded over          the period covered by this report.       *  Method of Measurement or Calculation: SeeSection 3 for the          definition of Discard RLE, andSection 4.1 of RFC 3611 for          RLE.       *  Units of Measurement: Every RTP packet in the interval is          reported as discarded or not.  SeeSection 3 for the          definition.       *  Measurement Point(s) with Potential Measurement Domain: The          measurement of these metrics is made at the receiving end of          the RTP stream.       *  Measurement Timing: Each RTP packet between a beginning          sequence number (begin_seq) and ending sequence number          (end_seq) is reported as discarded or not.  SeeSection 3 for          the definition of Discard RLE.       *  Use and applications: SeeSection 1, paragraph 1.       *  Reporting model: SeeRFC 3611.Ott, et al.                  Standards Track                   [Page 10]

RFC 7097                   RTCP XR Discard RLE              January 2014Authors' Addresses   Joerg Ott   Aalto University   School of Electrical Engineering   Otakaari 5 A   Espoo, FIN  02150   Finland   EMail: jo@comnet.tkk.fi   Varun Singh (editor)   Aalto University   School of Electrical Engineering   Otakaari 5 A   Espoo, FIN  02150   Finland   EMail: varun@comnet.tkk.fi   URI:http://www.netlab.tkk.fi/~varun/   Igor D.D. Curcio   Nokia Research Center   P.O. Box 1000 (Visiokatu 3)   Tampere, FIN  33721   Finland   EMail: igor.curcio@nokia.comOtt, et al.                  Standards Track                   [Page 11]

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