A. Clark Telchemy Internet Draft Document: draft-clark-avt-rtcpvoip-00 Expires: August 2002 February 2002 RTCP Extensions for Voice over IP Metric Reporting Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as work in progress. The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document specifies an extension to the Real-time Transport Control Protocol (RTCP) to support reporting of Voice over IP metrics from end-points. The proposed extension is useful for supporting both mid-call and end-of-call reporting of metrics for management and active control applications. 1. Conventions and Acronyms The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in RFC 2119. Clark Internet Draft - Expires 2002 [Page 1] RTCP Extensions for Voice over IP Metric Reporting 2. Introduction The Real-time Transport Protocol (RTP) [1] provides a real-time transport mechanism suitable for unicast or Internet Standard multicast communication between multimedia applications. Typical uses are for real-time or near real-time group communication via audio and video data streams. An important component of the RTP protocol is the control channel, defined as the Real-Time Control Protocol (RTCP). RTCP involves the periodic transmission of control packets between group members in a session, enabling the distribution or calculation of session specific information such as packet loss and round trip time to other hosts, and group size estimation. An additional advantage of providing a control channel for a session is that a third-party session monitor can listen to the traffic to establish network conditions and to diagnose faults based on receiver locations. Multimedia services, for example Voice over IP, are very sensitive to short term variations in network impairments such as packet loss and jitter. The use of adaptive jitter buffers and other impairment mitigation techniques can improve performance however make it very difficult to infer the behavior of the end to end connection from observations of the packet stream or from RTCP reported statistics. The extensions to RTCP described in this document provide concise but useful metrics for Voice over IP calls. 3. Basic Operation This draft proposes a small set of metrics that provide sufficient information to characterize a Voice over IP connection. The set of metrics includes:- 3.1 Packet loss metrics It has been shown [2] that the distribution of packet loss on the Internet can be reasonably approximated by a Markov Model. In the case of a Voice over IP connection it is necessary to consider both packets lost within the IP network and those discarded by a jitter buffer due to late arrival, overrun or underrun. (i) Packet loss rate (%) - a measure of the proportion of packets lost within the IP network (ii) Packet discard rate (%) - a measure of the proportion of packets discarded by the jitter buffer Clark Internet Draft - Expires 2002 [Page 2] RTCP Extensions for Voice over IP Metric Reporting Assume a Gilbert-Elliott model of the IP "channel" in which a "burst" is a period of time during which the number of packets received between two successive lost or discarded packets is less than some minimum Gmin [3]. This approach works well for Voice over IP as it treats isolated lost packets as distinct from periods of high packet loss - reflecting the effectiveness of packet loss concealment. (iii) Mean burst duration (mS)- the average length of a burst (iv) Mean burst density (%) - the proportion of packets lost within a burst (v) Mean gap duration (mS) - the average time between bursts (vi) Mean gap density (%) - the proportion of packets lost within a burst 3.2 Delay Delay is critical in interactive multimedia sessions. In general this comprises the transmission delay and the end-system delay. Users are generally not aware of asymmetry in delay and hence it is sufficient to report round trip delay. (vii) Round trip delay (mS) - as measured by RTCP (viii) End-system delay (mS) - including jitter buffer and encoding/ decoding delay 3.3 Analog metrics Analog metrics may be available in some systems (ix) Voice signal relative power (dB) (x) Echo level (xi) Noise level (xii) Distortion level 3.4 Voice Quality metrics Computing voice quality metrics in the end-system has the advantage that all the essential information is available and that time correlation is preserved. (xiii) Voice quality metric - Voice over IP segment (R factor) (xiv) Voice quality metric - Voice over IP segment (MOS score) (xv) Voice quality metric - External network (R factor) Clark Internet Draft - Expires 2002 [Page 3] RTCP Extensions for Voice over IP Metric Reporting 4. Extended Report Blocks 4.1 RTCP Report Format Metrics will be carried in an RTCP extended report block [4] An extended report block has the following format: 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 | type-specific | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : type-specific data : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ block type (BT): 8 bits = TBD Identifies the specific block format. type-specific: 8 bits The use of these bits is defined by the particular block type. length: 16 bits The length of this report block in 32-bit words minus one, including the header. type-specific data: variable length This MUST be a multiple of 32 bits long. It MAY be zero bits long. The encoding of the VoIP performance metrics consists of a six 32 bit words encoded using the following format. 4.2 Packet Loss and Discard Statistics Packet loss rate 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | loss rate | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The packet loss rate is defined as 10x the percentage of packets detected as lost at the receiving RTCP instance during the RTP session or VoIP call. For example, a value of 23 would correspond to a detected packet loss rate of 2.3% Clark Internet Draft - Expires 2002 [Page 4] RTCP Extensions for Voice over IP Metric Reporting Packet discard rate 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | discard rate | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The packet discard rate is defined as 10x the percentage of packets discarded due to underrun or buffer overflow at the receiving jitter buffer during the RTP session or VoIP call. For example, a value of 47 would correspond to a discard rate of 4.7% Mean burst duration (mS) 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | burst duration | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The mean burst duration is defined as the average period of time spent in a high loss state, i.e. a state in which the number of consecutive received packets between lost or discarded packets is less than some maximum value Gmin (default value 16). This parameter is expressed in milliseconds. Mean burst density 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | burst density | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Burst density is defined as 10x the percentage of packets lost or discarded whilst in the burst state. For example, a value of 100 would correspond to a loss density of 10.0% Clark Internet Draft - Expires 2002 [Page 5] RTCP Extensions for Voice over IP Metric Reporting Mean gap duration (mS) 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | gap duration | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The mean gap duration is defined as the average period of time spent in a low loss state, i.e. a state in which the number of consecutive received packets between lost or discarded packets is greater than some maximum value Gmin (default value 16). This parameter is expressed in milliseconds. Mean gap density 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | gap density | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Gap density is defined as 10x the percentage of packets lost or discarded whilst in the gap state. For example, a value of 3 would correspond to a loss density of 0.3% 4.3 Delay metrics Round trip delay (mS) 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RTD | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Round trip delay is defined as the delay measured between RTCP end points expressed in milliseconds. End-system delay (mS) 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | end system delay | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ End system delay is defined as the total encoding, decoding and jitter buffer delay determined at the end point. Clark Internet Draft - Expires 2002 [Page 6] RTCP Extensions for Voice over IP Metric Reporting 4.4 Analog signal metrics Voice signal relative power (dBm) 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Sig Power | +-+-+-+-+-+-+-+-+ The voice signal relative power is defined as the ratio of the peak signal power to overflow signal power expressed in dB as a signed 8 bit number. Echo level 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | echo level | +-+-+-+-+-+-+-+-+ The echo level is defined as the ratio of far end echo to transmit level expressed in dB as a signed 8 bit number. Noise level 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Noise level | +-+-+-+-+-+-+-+-+ The noise level is defined as the estimated silent period background noise level expressed in dBm as a signed 8 bit number. Distortion level 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | distortion | +-+-+-+-+-+-+-+-+ TBD Clark Internet Draft - Expires 2002 [Page 7] RTCP Extensions for Voice over IP Metric Reporting 4.5 Voice quality metrics Voice quality metric - Voice over IP segment R Factor 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | R Factor | +-+-+-+-+-+-+-+-+ Voice quality metric expressed as an R Factor Voice quality metric - Voice over IP segment MOS 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | MOS | +-+-+-+-+-+-+-+-+ Voice quality metric expressed as MOS x 10. For example a value of 35 would correspond to an estimated MOS score of 3.5 Voice quality metric - External network R Factor 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | R Factor | +-+-+-+-+-+-+-+-+ Voice quality metric related to an external network segment, for example a cellular network. 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | echo level | +-+-+-+-+-+-+-+-+ Clark Internet Draft - Expires 2002 [Page 8] RTCP Extensions for Voice over IP Metric Reporting 5. Acknowledgements 6. Intellectual Property The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 7. References [1] H. Schulzrinne, S. Casner, R. Frederick and V. Jacobson, "RTP: A transport protocol for real-time applications", RFC 1889, IETF, February 1996 [2] J. Bolot, S. Fosse-Parisis, D. Towsley "Adaptive FEC-Based Error Control for Interactive Audio in the Internet", IEEE Infocom 1999 [3] QoS Measurement for Voice over IP, ETSI TIPHON TS 101 329-5, December 2000 [4] T. Freidman, R. Caceres, K. Almeroth, K. Sarac, "RTCP Reporting Extensions", draft-friedman-avt-rtcp-report-extns-02.txt Clark Internet Draft - Expires 2002 [Page 9] RTCP Extensions for Voice over IP Metric Reporting 8 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." 9. Authors' Addresses Alan Clark Telchemy Incorporated 3360 Martins Farm Road, Suite 200 Suwanee, GA 30024 Clark Internet Draft - Expires 2002 [Page 10]