INTERNET-DRAFT R. Huang Intended Status: Standard Huawei Expires: August 17, 2014 V. Singh Aalto University February 13, 2014 RTP Control Protocol (RTCP) Extended Report (XR) for Post-Repair Loss Count Metrics draft-ietf-xrblock-rtcp-xr-post-repair-loss-count-01 Abstract This document defines an RTP Control Protocol (RTCP) Extended Report (XR) Block that allows reporting of post-repair loss count metrics for a range of RTP applications. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. 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Table of Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 Post-Repair Loss Count Metrics Report Block . . . . . . . . . . 4 4 SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1 SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . . 5 4.2 Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . 6 5 Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6.1 New RTCP XR Block Type value . . . . . . . . . . . . . . . 6 6.2 New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . . 7 6.3 Contact Information for registrations . . . . . . . . . . . 7 7 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1 Normative References . . . . . . . . . . . . . . . . . . . 7 8.2 Informative References . . . . . . . . . . . . . . . . . . 7 Appendix A. Metrics Represented Using the Template from RFC 6390 . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 Expires August 17, 2014 [Page 2] INTERNET DRAFT Post-Repair Non-RLE loss Count February 13, 2014 1 Introduction RTCP SR/RR [RFC3550] contains some rough statistics about the data received from the particular source indicated in that block. One of them is the cumulative number of packet lost, which is called pre- repair loss metric in this document. This metric conveys information regarding the total number of RTP data packets that have been lost since the beginning of the RTP session. However, this metric is measured on media stream before any loss repair mechanism, e.g., retransmission [RFC4588] and Forward Error Correction (FEC) [RFC5109], is applied. Using a repair mechanism usually results in recovering some or all of the lost packets. Hence, the sending endpoint cannot assess the performance of the repair mechanism by observing the change in fraction loss and the cumulative loss statistics from RTCP SR/RR [RFC3550]. Consequently, [RFC5725] specifies a post-repair loss Run-length Encoding (RLE) XR report block to address this issue. The sending endpoint is able to infer which packets were repaired from the RLE report block, but at the cost of higher overhead. When applications use multiple XR blocks, the endpoints may require more concise reporting to save bandwidth. This document defines a new XR block type to augment those defined in [RFC3611] and complement the report block defined in [RFC5725] for use in a range of RTP application. This new block type reports the number of primary source RTP packets that are still lost after applying one or more loss repair mechanisms. When comparing this metric with pre-repair loss metric of RTCP SR/RR, ambiguity may occur as noted in [RFC5725]: Some packets will not be repaired in current RTCP interval. Thus it is RECOMMENDED that this report block should be generated for those source packets that have no further chance of being repaired. But a potential ambiguity may result from sequence number range inconsistent. The sequence number range reported by RTCP SR/RR may contain some sequence numbers of packets for which repair might still be possible. To address this issue, we use begin sequence number and end sequence number to explicitly indicate the actual sequence number range that this RTCP XR report block reports on. In addition, another metric, repaired loss count, is also introduced in this report block for calculating the pre-repair loss count during the this range, so that the RTP sender or a third-party entity is able to evaluate the effectiveness of the repair methods used by the system. Note that the metrics in this report block MUST NOT be directly compared with the pre-repair loss metric of [RFC3550]. The metrics defined in this document belongs to the class of transport-related metrics defined in [RFC6792]. And it is in accordance with the guidelines in [RFC6390] and [RFC6792]. These metrics are applicable to any RTP application, especially those that use loss repair mechanisms. Expires August 17, 2014 [Page 3] INTERNET DRAFT Post-Repair Non-RLE loss Count February 13, 2014 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 in RFC 2119 [RFC2119]. primary source RTP packet: the original RTP packet sent from the RTP sender for the first time. A primary source RTP packet may be lost when transporting. The lost one can be repaired by mechanisms like FEC or retransmission. 3 Post-Repair Loss Count Metrics Report Block This block reports the number of packets lost after applying repair mechanisms to complement the RTCP XR metrics defined in [RFC5725]. This packet may be stacked with other RTCP packets to form compound RTCP packets and share the average reporting interval calculated by the RTCP method described in [RFC3550]. These metrics defined in this report block are all interval metrics and the measurement of them is made at the receiving end of the RTP stream. The post-repair loss count metrics report block has the following format: 0 1 2 3 4 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 0 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | BT=PRLR | Reserved | block length = 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC of Source | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | begin_seq | end_seq | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | unrepaired loss count | repaired loss count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Format for the Post-Repair Loss Count Metrics Report Block Block Type (BT): 8 bits A Post-Repair Loss Count Metrics Report Block is identified by the constant PRLR. [Note to RFC Editor: Please replace PRLR with the IANA provided RTCP XR block type for this block.] Expires August 17, 2014 [Page 4] INTERNET DRAFT Post-Repair Non-RLE loss Count February 13, 2014 Reserved: 8 bits These bits are reserved for future use. They MUST be set to zero by senders and ignored by receivers (see [RFC6709], Section 4.2). block length: 16 bits This field is in accordance with the definition in [RFC3611]. In this report block, it MUST be set to 4. The block MUST be discarded if the block length is set to a different value. SSRC of source: 32 bits As defined in Section 4.1 of [RFC3611]. begin_seq: 16 bits The first sequence number that this block reports on. end_seq: 16 bits The last sequence number that this block reports on plus one. unrepaired loss count: 16 bits Total number of packets finally lost after one or more loss-repair methods, e.g., FEC and/or retransmission, during this interval. This metric MUST NOT count the lost packets for which repair might still be possible. Note that this metric must be measured in the primary source RTP packets. repaired loss count: 16 bits Total number of packets fully repaired after one or more loss- repair methods, e.g., FEC and/or retransmission, during this interval. Note that this metric must be measured in the primary source RTP packets. 4 SDP Signaling [RFC3611] defines the use of SDP (Session Description Protocol) for signaling the use of RTCP XR blocks. However XR blocks MAY be used without prior signaling (see section 5 of [RFC3611]). 4.1 SDP rtcp-xr-attrib Attribute Extension This session augments the SDP attribute "rtcp-xr" defined in Section Expires August 17, 2014 [Page 5] INTERNET DRAFT Post-Repair Non-RLE loss Count February 13, 2014 5.1 of [RFC3611] by providing an additional value of "xr-format" to signal the use of the report block defined in this document. xr-format =/ xr-prlr-block xr-prlr-block = "post-repair-loss-count" 4.2 Offer/Answer Usage When SDP is used in offer-answer context, the SDP Offer/Answer usage defined in [RFC3611] for unilateral "rtcp-xr" attribute parameters applies. For detailed usage of Offer/Answer for unilateral parameter, refer to section 5.2 of [RFC3611]. 5 Security Considerations It is believed that this RTCP XR block introduces no new security considerations beyond those described in [RFC3611]. This block does not provide per-packet statistics, so the risk to confidentially documented in Section 7, paragraph 3 of [RFC3611] does not apply. An attacker may put incorrect information in the Post-Repair Loss Count reports, which will be affect the performance of loss repair mechanisms. Implementers should consider the guidance in [I-D.ietf- avtcore-srtp-not-mandatory] 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 in [RFC3711]; an appropriate combination of the two profiles (an "SAVPF") is specified in [RFC5124]. However, other mechanisms also exist (documented in [I- D.ietf-avtcore-rtp-security-options]) and might be more suitable. 6 IANA Considerations New block types for RTCP XR are subject to IANA registration. For general guidelines on IANA considerations for RTCP XR, refer to [RFC3611]. 6.1 New RTCP XR Block Type value This document assigns the block type value PRLR in the IANA "RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry" to the "Post-Repair Loss Count Metrics Report Block". [Note to RFC Editor: please replace PRLR with the IANA provided RTCP XR block type for this block.] Expires August 17, 2014 [Page 6] INTERNET DRAFT Post-Repair Non-RLE loss Count February 13, 2014 6.2 New RTCP XR SDP Parameter This document also registers a new parameter "post-repair-loss-count" in the "RTP Control Protocol Extended Reports (RTCP XR) Session Description Protocol (SDP) Parameters Registry". 6.3 Contact Information for registrations The following contact information is provided for all registrations in this document: Rachel Huang (rachel.huang@huawei.com) 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China 7 Acknowledgments The author would like to thank Roni Even and Colin Perkins for giving valuable comments and suggestions. 8 References 8.1 Normative References [KEYWORDS] 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., Ed., Caceres, R., Ed., and A. Clark, Ed., "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, November 2003. [RFC5725] Begen, A., Hsu, D., and M. Lague, "Post-Repair Loss RLE Report Block Type for RTP Control Protocol (RTCP) Extended Reports (XRs)", RFC 5725, February 2010. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. 8.2 Informative References Expires August 17, 2014 [Page 7] INTERNET DRAFT Post-Repair Non-RLE loss Count February 13, 2014 [RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New Performance Metric Development", BCP 170, RFC 6390, October 2011. [RFC6792] Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the RTP Monitoring Framework", RFC 6792, November 2012. Appendix A. Metrics Represented Using the Template from RFC 6390 a. Unrepaired RTP Packet Loss Count Metric * Metric Name: Unrepaired RTP Packet Loss Count Metric * Metric Description: Total number of RTP packets still lost after loss repair methods are applied * Method of Measurement or Calculation: It must be measured for the primary source RTP packets with no further chance of repair * Units of Measurement: See section 3, unrepaired loss count definition * Measurement Point(s) with Potential Measurement Domain: See section 3, 1st paragraph * Measurement Timing: See Section 3, 1st paragraph, for measurement timing * Use and Applications: See Section 1 * Reporting Model: See RFC3611 b. Repaired RTP Packet Loss Count Metric * Metric Name: Repaired RTP Packet Count Metric * Metric Description: The number of RTP packets lost but repaired after applying loss repair methods * Method of Measurement or Calculation: It must be measured for the primary source RTP packets with no further chance of repair * Units of Measurement: See section 3, repaired loss count definition * Measurement Point(s) with Potential Measurement Domain: See section 3, 1st paragraph Expires August 17, 2014 [Page 8] INTERNET DRAFT Post-Repair Non-RLE loss Count February 13, 2014 * Measurement Timing: See Section 3, 1st paragraph, for measurement timing * Use and Applications: See Section 1 * Reporting Model: See RFC3611 Authors' Addresses Rachel Huang Huawei 101 Software Avenue, Yuhua District Nanjing 210012 China EMail: rachel.huang@huawei.com Varun Singh 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/ Expires August 17, 2014 [Page 9]