Network Working Group H. Zheng Internet-Draft R. Even Intended status: Informational Q. Wu Expires: May 3, 2018 Huawei R. Gu China Mobile October 30, 2017 RTP Control Protocol (RTCP) Extended Report (XR) Block for Effective Loss Index Reporting draft-zheng-xrblock-effective-loss-index-00 Abstract This document defines a new metric for RTP applications to measure the effectiveness of stream repair means, and an RTP Control Protocol (RTCP) Extended Report (XR) Block to report the metric. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on May 3, 2018. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 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 Zheng, et al. Expires May 3, 2018 [Page 1] Internet-Draft RTCP XR Effective Loss Index October 2017 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Effective Loss Index . . . . . . . . . . . . . . . . . . 3 1.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 4 1.3. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . 5 1.4. Performance Metrics Framework . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Effective Loss Index Report Block . . . . . . . . . . . . . . 5 4. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . 6 4.2. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6.1. New RTCP XR Block Type Value . . . . . . . . . . . . . . 7 6.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 8 6.3. Contact Information for Registrations . . . . . . . . . . 8 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 8.1. Normative References . . . . . . . . . . . . . . . . . . 8 8.2. Informative References . . . . . . . . . . . . . . . . . 8 Appendix A. Metric Represented Using the Template from RFC 6390 10 A.1. Effective Loss Index . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction RTP applications often use stream repair means, e.g. FEC (Forward Error Correction) [RFC5109] and/or retransmission [RFC4588] to improve the robustness of media streams. With the presence of those stream repair means, a degree of packet loss can be recovered for a media stream. In the past, some RTCP Extend Reports (XRs) were defined to reflect the situation of post-repair loss. For example, [RFC5725] defines an XR block using Run Length Encoding (RLE) to report post-repair loss; [RFC7509] defines count metrics for post- repair loss. This document proposes a new metric Effective Loss Index (ELI) to measure the effectiveness of stream repair means. The new metric provides a simpler view on the post-repair loss than the mechanisms documented in [RFC5725] and [RFC7509]. EFI is an index, so the values reported from different RTP sources can be compared directly, which makes it easier to rank the effectiveness of loss repair means. An example use case is to find endpoints whose ELI values are at bottom 10%. For those endpoints, more informative XR reports such as Zheng, et al. Expires May 3, 2018 [Page 2] Internet-Draft RTCP XR Effective Loss Index October 2017 those in [RFC5725] and [RFC7509] can then be used to discover more details about the loss situations. This document also defines an XR block to report the metric, which can be found out in Section 3. 1.1. Effective Loss Index Effective Loss Index (ELI) uses a simple model to measure the effectiveness of loss repair. The model assumes that repair means are applied onto packets by batches of equal size. Lower ELI means that the repair was more successful. Specifically, a batch is identified by a range of RTP sequence numbers. The size of a batch is number of packets. An application can agree upon a default batch size, or use the SDP signaling defined in Section 4.1 to communicate one. An RTP endpoint is thought to process received packets and apply repair means batch by batch. For each batch, if there is still some unrecoverable loss after having applied the repair means, then the repair means are deemed as ineffective. The ineffectiveness is denoted by Effective Loss Factor (ELF), along with a parameter Effective Loss Threshold, showing below: if Post-Repair Loss > Effective Loss Threshold Effective Loss Factor = 1 else Effective Loss Factor = 0 endif Figure 1: Calculation of Effective Loss Factor The parameters in Figure 1 are explained below: o Post-Repair Loss is the number of packet lost after repair in the batch. o Effective Loss Threshold is in number of packets. The minimum value of Effective Loss Threshold is zero. This document does not mandate any value for Effective Loss Threshold. Applications can prescribe a value for themselves without signaling. On the other hand, SDP signaling defined in Section 4.1 can be used to communicate the value. Determining an Effective Loss Threshold value for use can be empirical, applications may have to try out and change the value from time to time, depending on their needs. Zheng, et al. Expires May 3, 2018 [Page 3] Internet-Draft RTCP XR Effective Loss Index October 2017 Effective Loss Index is an integer derived by calculating the average Effective Loss Factor across a sequence of consecutive batches of RTP packets. Let ELF(i) be the Effective Loss Factor calculated for i-th batch, and N as number of batches in the sequence, then Effective Loss Index is calculated as: ELF(1)+ELF(2)+ ...+ELF(N) Effective Loss Index = ------------------------- x 10000 N Figure 2: Calculation of Effective Loss Index The following is an example of how to calculate Effective Loss Index. For simplicity and demonstration purpose, the size of batches is assumed to be 3, and the Effective Loss Threshold is assumed to be 1. The example processes a sequence of 9 RTP packets in 3 batches. Batch Post-Repair Effective Loss Loss Factor | 1 2 3 | 2, 3 1 | 4 5 6 | 5 0 | 7 8 9 | 7 0 1 + 0 + 0 Effective Loss Index = ----------- x 10000 = 3333 3 1.2. Applicability The metric defined by this document is applicable to a range of RTP applications that send packets in batches of equal length, probably with stream repair means (e.g., Forward Error Correction (FEC) [RFC5109] and/or retransmission [RFC4588]) applied on the batches. Note that in order to not interfere with the batches being protected, any additional packets generated by the stream repair means SHOULD be in a different RTP stream. The number of batches among which ELI is calculated should not be too few, otherwise the result may be too biased. However, specifying a minimal number of batches seems unrealistic, due to the stream repair means used by applications can be quite different. This document leaves it to applications to choose a suitable minimal value for the number of batches. Zheng, et al. Expires May 3, 2018 [Page 4] Internet-Draft RTCP XR Effective Loss Index October 2017 1.3. RTCP and RTCP XR Reports The use of RTCP for reporting is defined in [RFC3550]. [RFC3611] defines an extensible structure for reporting by using an RTCP Extended Report (XR). This document defines a new Extended Report block for use with [RFC3550] and [RFC3611]. 1.4. Performance Metrics Framework The Performance Metrics Framework [RFC6390] provides guidance on the definition and specification of performance metrics. The "Guidelines for Use of the RTP Monitoring Framework" [RFC6792] provides guidelines for reporting block format using RTCP XR. The Metrics Block described in this document is in accordance with the guidelines in [RFC6390] and [RFC6792]. 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]. 3. Effective Loss Index Report Block The Effective Loss Index 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=TBD | Reserved | Block length = 3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC of Source | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Effective Loss Index | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Block Type (BT): 8 bits: An Effect Loss Index Report Block is identified by the constant 'TBD'. [[Editor Note: should replace 'TBD' with assigned value]] Reserved: 8 bits: These bits are reserved for future use. They MUST be set to zero by senders and ignored by receivers (see Section 4.2 of [RFC6709]). Block length: 16 bits: This field is in accordance with the definition in [RFC3611]. In this report block, it MUST be set to Zheng, et al. Expires May 3, 2018 [Page 5] Internet-Draft RTCP XR Effective Loss Index October 2017 3. 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]. Effective Loss Index: 16 bits: The value of this field SHOULD be set to the calculated result of Effective Loss Index (as in Figure 2). Padding: 16 bits: These bits MUST be set to zero by senders and ignored by receivers. 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 5.1 of [RFC3611] by providing an additional value of "xr- format" to signal the use of the report block defined in this document. The ABNF [RFC5234] syntax is as follows. xr-format =/ xr-eli-block xr-eli-block = "effective-loss-index" [ ":" effective-loss-batch-size] [ ">" effective-loss-threshold] effective-loss-batch-size = 1*DIGIT ; the batch size is in number of packets effective-loss-threshold = 1*DIGIT ; the threshold is in number of packets DIGIT = %x30-39 The SDP attribute "xr-eli-block" is designed to contain two optional values, one for signaling the batch size, another for the Effective Loss Threshold. Here are some examples: Zheng, et al. Expires May 3, 2018 [Page 6] Internet-Draft RTCP XR Effective Loss Index October 2017 1. signaling both batch size (100) and Effective Loss Threshold (2) xr-eli-block = "effective-loss-index" : "100" > "2" 2. signaling only batch size (100) xr-eli-block = "effective-loss-index" : "100" 3. signaling only Effective Loss Threshold (2) xr-eli-block = "effective-loss-index" > "2" 4.2. Offer/Answer Usage When SDP is used in offer/answer context, the SDP Offer/Answer usage defined in [RFC3611] for the unilateral "rtcp-xr" attribute parameters applies. For detailed usage of Offer/Answer for unilateral parameters, refer to Section 5.2 of [RFC3611]. 5. Security Considerations This proposed 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 confidentiality documented in Section 7, paragraph 3 of [RFC3611] does not apply. An attacker may put incorrect information in the Effective Loss Index reports. Implementers should consider the guidance in [RFC7202] 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 [RFC7201] 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 'TBD' in the IANA "RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry" to the "Post-Repair Loss Count Metrics Report Block". Zheng, et al. Expires May 3, 2018 [Page 7] Internet-Draft RTCP XR Effective Loss Index October 2017 [[Editor Note: should replace 'TBD' with assigned value]] 6.2. New RTCP XR SDP Parameter This document also registers a new parameter "effective-loss-index" in the "RTP Control Protocol Extended Reports (RTCP XR) Session Description Protocol (SDP) Parameters Registry". 6.3. Contact Information for Registrations The contact information for the registrations is: RAI Area Directors 7. Acknowledgements This document has benefited greatly from the comments of various people. The following individuals have contributed to this document: Rachel Huang, Colin Perkins, Yanfang Zhang, Lingyan Wu. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, July 2003, . 8.2. Informative References [RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed., "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, DOI 10.17487/RFC3611, November 2003, . [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, DOI 10.17487/RFC3711, March 2004, . Zheng, et al. Expires May 3, 2018 [Page 8] Internet-Draft RTCP XR Effective Loss Index October 2017 [RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. Hakenberg, "RTP Retransmission Payload Format", RFC 4588, DOI 10.17487/RFC4588, July 2006, . [RFC5109] Li, A., Ed., "RTP Payload Format for Generic Forward Error Correction", RFC 5109, DOI 10.17487/RFC5109, December 2007, . [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February 2008, . [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, . [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, DOI 10.17487/RFC5725, February 2010, . [RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New Performance Metric Development", BCP 170, RFC 6390, DOI 10.17487/RFC6390, October 2011, . [RFC6709] Carpenter, B., Aboba, B., Ed., and S. Cheshire, "Design Considerations for Protocol Extensions", RFC 6709, DOI 10.17487/RFC6709, September 2012, . [RFC6792] Wu, Q., Ed., Hunt, G., and P. Arden, "Guidelines for Use of the RTP Monitoring Framework", RFC 6792, DOI 10.17487/RFC6792, November 2012, . [RFC7201] Westerlund, M. and C. Perkins, "Options for Securing RTP Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014, . [RFC7202] Perkins, C. and M. Westerlund, "Securing the RTP Framework: Why RTP Does Not Mandate a Single Media Security Solution", RFC 7202, DOI 10.17487/RFC7202, April 2014, . Zheng, et al. Expires May 3, 2018 [Page 9] Internet-Draft RTCP XR Effective Loss Index October 2017 [RFC7509] Huang, R. and V. Singh, "RTP Control Protocol (RTCP) Extended Report (XR) for Post-Repair Loss Count Metrics", RFC 7509, DOI 10.17487/RFC7509, May 2015, . Appendix A. Metric Represented Using the Template from RFC 6390 A.1. Effective Loss Index o Metric Name: RTP Effective Loss Index. o Metric Description: The effectiveness of stream repair means applied on a sequence of RTP packets. o Method of Measurement or Calculation: See the "Effective Loss Index" definition in Section 1.1. It is directly measured and must be measured for the primary source RTP packets with no further chance of repair. o Units of Measurement: This metric is expressed as a 16-bit unsigned integer value representing the effectiveness of stream repair means. o Measurement Point(s) with Potential Measurement Domain: It is measured at the receiving end of the RTP stream. o Measurement Timing: This metric relies on the sequence number interval to determine measurement timing. o Use and Applications: These metrics are applicable to any RTP application, especially those that use loss-repair mechanisms. See Section 1 for details. o Reporting Model: See RFC 3611. Authors' Addresses Hui Zheng (Marvin) Huawei Email: marvin.zhenghui@huawei.com Roni Even Huawei Email: roni.even@huawei.com Zheng, et al. Expires May 3, 2018 [Page 10] Internet-Draft RTCP XR Effective Loss Index October 2017 Qin Wu Huawei Email: bill.wu@huawei.com Rong Gu China Mobile Email: gurong_cmcc@outlook.com Zheng, et al. 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