AVT Working Group Alan Clark Internet Draft Telchemy Geoff Hunt BT Intended status: Standards Track October 26, 2008 Expires: April 28, 2008 RTCP XR Report Block for Signal Level Metrics Reporting draft-ietf-avt-rtcp-xr-siglevel-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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. 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 This Internet-Draft will expire on April 28, 2009. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract This document defines an RTCP XR Report Block that allows the reporting of metrics related to signal levels for use in voice, audio and video services. 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 [1]. Clark & Hunt [Page 1] RTCP XR Signal Level Metrics October 2008 1. Introduction 1.1. Signal Level Report Block This draft defines a new block types to augment those defined in RFC3611 for use in reporting the level of signal/ decoded payload related metrics. Signal level metrics include, for example, signal level, background noise level and echo level. These metrics are useful when determing, for example: (a) if there is a problem with the input to an encoder being set to an excessively high or low level (b) if the input to the encoder is faulty (e.g. disconnected) (c) if the source signal is excessively noisy (d) if there is a significant level of echo that would be disruptive during an IP telephone call or audio conference 1.2. RTCP and RTCP XR Reports The use of RTCP for reporting is defined in RFC3550 [2]. RFC3611 [3] defined an extensible structure for reporting using an RTCP Extended Report (XR). This draft defines a new Extended Report block that MUST be used as defined in RFC3550 and RFC3611. 1.3 Performance Metrics Framework The Performance Metrics Framework [n] provides guidance on the definition and specification of performance metrics. Metrics described in this draft either reference external definitions or define metrics generally in accordance with the guidelines in [4]. 1.4 Applicability This memo applies to any application of RTP in which there is an audio or speech component. 2. Definitions 2.1 Signal Level The "signal" is defined as the active "talkspurts" within an interactive voice stream or the whole of a unidirectional audio or video stream. "Noise" is the additive background noise level, which can be measured either during silence periods between periods of audio/ voice activity or Clark & Hunt [Page 2] RTCP XR Signal Level Metrics October 2008 otherwise extracted from the signal. 2.1 Mean Signal Level Mean Signal Level is defined as the mean power level of the signal, expressed in dBm. In telephony applications the power level is typically expressed with reference to a zero reference point in dBm0. 2.2 Peak Signal Level Peak signal Level is defined as the peak power level of the signal, expressed in dBm. 2.3 Noise Level Noise Level is defined as the power level of the additive or silent period noise expressed in dBm. In telephony applications the noise level is typically expressed with reference to a zero reference point in dBm0. 2.4 Echo Level 2.5 Channel Certain types of encoder (for example stereo audio codecs) incorporate multiple audio or video channels into a single encoded stream which is then packetized and carried in RTP or MPEG Transport. Within the scope of this memo, the term "channel" applies to this definition only - if multiple audio or video streams are carried either in separate RTP sessions (identified by an SSRC) or MPEG Transport program streams (identified by a PID) then the Measurement Identifier block MUST be used to identify the stream to which metrics apply. 3. Signal Level Metrics Block 3.1 Report Block Structure 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=N |C|T|T|T| | block length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |s s s s|c c c c c c|m m|d d|b b| Level | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ............ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |s s s s|c c c c c c|m m|d d|b b| Level | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ssss = Reported signal level metric type Clark & Hunt [Page 3] RTCP XR Signal Level Metrics October 2008 0000 - active signal level 0001 - overall signal level 0010 - noise level 0011 - echo return loss 0100 - residual echo return loss (ACOM) 0101 - Y signal level 0110 - Cb signal level 0111 - Cr signal level - other values reserved cccccc = channel number 000000 - 011111 Channel number range 100000 - 111111 reserved mm = measured or default value 00 - sampled value 01 - average value 10 - default or configured value 11 - reserved dd = direction 00 - Received signal (this RTP session) 01 - Received signal (external) 10 - Transmitted signal (this RTP session) 11 - Transmitted signal (external) bb = metric scaling 00 - dBm0 01 - dBm 10 - dBov 11 - reserved 3.2 Definition of Fields in Signal Level Metric Report Block block type (BT): 8 bits A Signal Level Report Block is identified by the constant SLMT. [Note to RFC Editor: please replace SLMT with the IANA provided RTCP XR block type for this block.] Interval Metric flag (I): 1 bit This field is used to indicate whether the Basic Loss/Discard metrics are Interval or Cumulative metrics, that is, whether the reported values applies to the most recent measurement interval duration between successive metrics reports (I=1) (the Interval Duration) or to the accumulation period characteristic of cumulative measurements (I=0) (the Cumulative Duration). Numerical values for both these intervals are provided in the Clark & Hunt [Page 4] RTCP XR Signal Level Metrics October 2008 Measurement Identifier block referenced by the tag field below. Measurement Identifier association (tag): 3 bits This field is used to identify the Measurement Identifier block which describes this measurement. The relevant Measurement Identifier block has the same tag value as the Basic Loss/Discard block. Note that there may be more than one Measurement Identifier block per RTCP packet. Block length: 16 bits The length if this report block in 32-bit words minus one. Signal level metrics words A Signal Level Metrics report block may contain one or more sets of signal level metrics, each contained in a single 32 bit word. Reported signal level metric type The signal level metric type may have the following values: 0000 - active signal level This indicates that the reported metric is the signal level during active periods, for example talkspurts during speech 0001 - overall signal level This indicates that the reported metric is the signal level measured for the reporting interval, with no distinction made between active signal and silent periods. This would be more appropriate for an audio or video signal. 0010 - noise level This indicates that the reported metric is the noise level, which could for example be measured during periods of low signal activity. 0011 - echo return loss This indicates that the reported metric is the uncanceled echo return loss. 0100 - residual echo return loss (ACOM) This indicates that the reported metric is the echo return loss measured after echo cancellation. 0101 - Y signal level This indicates that the reported metric is the level of the Y or Luminance component of a video signal. Clark & Hunt [Page 5] RTCP XR Signal Level Metrics October 2008 0110 - Cb signal level This indicates that the reported metric is the level of the Cb chrominance component of a video signal. 0111 - Cr signal level This indicates that the reported metric is the level of the Cr chrominance component of a video signal. Channel number The number associated with a channel within the audio, speech or video signal. For example, this could be used to indicate one of the two channels of a stereo audio signal. Measured or default value This field indicates that the reported value is either an sampled value, an average over the measurement interval or a default or configured value. Direction The Direction field indicates whether the metric refers to the received or transmitted signal, and whether the value has been measured for "this" RTP session (i.e. the session to which the RTCP reports relate) or are "external" to the RTP session. Metric scaling The Metric Scaling field indicates the scaling or reference used for the metric. 00 - dBm0 - dB with reference to a milliwatt at the zero reference point. 01 - dBm - dB with reference to a milliwatt. 10 - dBov - dB with reference to the overflow or maximum level that can be represented within a digital system. 11 - reserved Level The value of the metric in signed 8:8 scaled signed integer representation. This permits a range of +/- 127.996 dB to be reported. Measurement methodologies are defined in references [5][6][7][8]. 4. SDP Signaling RFC3611 [3] defines the use of SDP (Session Description Protocol) Clark & Hunt [Page 6] RTCP XR Signal Level Metrics October 2008 [4] for signaling the use of XR blocks. XR blocks MAY be used without prior signaling. This section augments the SDP [4] attribute "rtcp-xr" defined in RFC3611[3] by providing a "xr-format" to signal the use of the report block defined in this document. rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF (defined in RFC3611) xr-format = xr-format / siglev-metrics siglev-metrics = "siglev-metrics" [EQUAL word] DIGIT = %x30-39 format-ext = non-ws-string non-ws-string = 1*(%x21-FF) CRLF = %d13.10 5. IANA Considerations This document creates a new block type within the IANA "RTCP XR Block Type Registry" called the QoE Metrics, and a new [new-xrblock] parameter within the "RTCP XR SDP Parameters Registry". 6. Security Considerations RTCP reports can contain sensitive information since they can provide information about the nature and duration of a session established between two or more endpoints. 7. Contributors 8. References Normative [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [3] Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, November 2003. [4] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 4566, July 2006. Clark & Hunt [Page 7] RTCP XR Signal Level Metrics October 2008 [5] ITU-T Recommendation G.168 "Digital Network Echo Cancellers" [6] ITU-T Recommendation P.56 "Objective Measurement of Active Speech Level" [7] ITU-T Recommendation P.561 "In-Service, Non-Intrusive Measurement Device - Voice Service Measurements" [8] ITU-R BS.2054 "Audio levels and loudness" Informative [9] Clark, A. "Framework for Performance Metric Development draft-ietf-pmol-perf-metrics-framework-00.txt Author's Addresses Alan Clark Telchemy Incorporated 2905 Premiere Parkway, Suite 280 Duluth, GA 30097 USA Email: alan.d.clark@telchemy.com Geoff Hunt BT Orion 1 PP9 Adastral Park Martlesham Heath Ipswich, Suffolk IP4 2TH United Kingdom Email: geoff.hunt@bt.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights 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; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Clark & Hunt [Page 8] RTCP XR Signal Level Metrics October 2008 Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Clark & Hunt [Page 9]