Internet Engineering Task Force (IETF) A. Clark Request for Comments: 7266 Telchemy Category: Standards Track Q. Wu ISSN: 2070-1721 Huawei R. Schott Deutsche Telekom G. Zorn Network Zen June 2014 RTP Control Protocol (RTCP) Extended Report (XR) Blocks for Mean Opinion Score (MOS) Metric Reporting
AbstractThis document defines an RTP Control Protocol (RTCP) Extended Report (XR) Block including two new segment types and associated Session Description Protocol (SDP) parameters that allow the reporting of mean opinion score (MOS) Metrics for use in a range of RTP applications. 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 in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7266.
Copyright Notice Copyright (c) 2014 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 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 1. Introduction ....................................................3 1.1. MOS Metrics Report Block ...................................3 1.2. RTCP and RTCP XR Reports ...................................3 1.3. Performance Metrics Framework ..............................3 1.4. Applicability ..............................................3 2. Terminology .....................................................4 2.1. Standards Language .........................................4 3. MOS Metrics Block ...............................................5 3.1. Report Block Structure .....................................6 3.2. Definition of Fields in MOS Metrics Block ..................6 3.2.1. Single-Channel Audio/Video per SSRC Segment .........7 3.2.2. Multi-Channel Audio per SSRC Segment ................9 4. SDP Signaling ..................................................10 4.1. SDP "rtcp-xr-attrib" Attribute Extension ..................10 4.2. Offer/Answer Usage ........................................12 5. IANA Considerations ............................................14 5.1. New RTCP XR Block Type Value ..............................14 5.2. New RTCP XR SDP Parameter .................................14 5.3. The SDP "calgextmap" Attribute ............................14 5.4. New Registry of Calculation Algorithms ....................15 6. Security Considerations ........................................16 7. Contributors ...................................................16 8. Acknowledgements ...............................................17 9. References .....................................................17 9.1. Normative References ......................................17 9.2. Informative References ....................................18 Appendix A. Metrics Represented Using the RFC 6390 Template .......20
RFC3611], for use in a range of RTP applications. The new block type provides information on media quality using one of several standard metrics (e.g., mean opinion score (MOS)). The metrics belong to the class of application-level metrics defined in [RFC6792]. RFC3550]. RFC 3611 defined an extensible structure for reporting using an RTCP Extended Report (XR). This document defines a new Extended Report block for use with [RFC3550] and [RFC3611]. RFC6390] provides guidance on the definition and specification of performance metrics. The RTP Monitoring Architectures document [RFC6792] provides guidelines for reporting block format using RTCP XR. The XR block type described in this document is in accordance with the guidelines in [RFC6390] and [RFC6792].
media streams, or it may be estimated using algorithms that model the interaction between media quality, protocol, and encoded content. Media quality is commonly expressed in terms of MOS; however, it is also represented by a range of indexes and other scores. The measurement of media quality has a number of applications: o Detecting problems with media delivery or encoding that is impacting user-perceived quality. o Tuning the content encoder algorithm to satisfy real-time data quality requirements. o Determining which system techniques to use in a given situation and when to switch from one technique to another as system parameters change (for example, as discussed in [G.1082]). o Prequalifying a network to assess its ability to deliver an acceptable end-user-perceived quality level. RFC2119]. Notable terminology used is the following. Numeric formats X:Y where X the number of bits prior to the decimal place and Y the number of bits after the decimal place. Hence, 8:8 represents an unsigned number in the range 0.0 to 255.996 with a granularity of 0.0039. 0:16 represents a proper binary fraction with range 0.0 to 1 - 1/65536 = 0.9999847, though note that use of flag values at the top of the numeric range slightly reduces this upper limit. For example, if the 16-bit values 0XFFFE and 0XFFFF are used as flags for "over- range" and "unavailable" conditions, a 0:16 quantity has range 0.0 to 1 - 3/65536 = 0.9999542. Calculation Algorithm Calculation Algorithm is used in this document to mean the MOS or QoE estimation algorithm.
BS.1387-1], [G.107], [G.107.1], [P.862], [P.862.1], [P.862.2], [P.863], [P.564], [G.1082], [P.1201.1], [P.1201.2], [P.1202.1], [P.1202.2]) define methodologies for assessment of the performance of audio and video streams. Other international and national standards organizations such as EBU, ETSI, IEC, and IEEE also define QoE algorithms and methodologies, and the intent of this document is not to restrict its use to ITU recommendations but to suggest that ITU recommendations be used where they are defined. This block reports the media quality in the form of a MOS range (e.g., 1-5, 0-10, or 0-100, as specified by the calculation algorithm); however, it does not report the MOS that includes parameters outside the scope of the RTP stream, for example, signaling performance, mean time to repair (MTTR), or other factors that may affect the overall user experience. The MOS Metric reported in this block gives a numerical indication of the perceived quality of the received media stream, which is typically measured at the receiving end of the RTP stream. Instances of this Metrics Block refer by synchronization source (SSRC) to the separate auxiliary Measurement Information block [RFC6776] which describes measurement periods in use (see RFC 6776, Section 4.2). This Metrics Block relies on the measurement period in the Measurement Information block indicating the span of the report. Senders MUST send this block in the same compound RTCP packet as the Measurement Information block. Receivers MUST verify that the measurement period is received in the same compound RTCP packet as this Metrics Block. If not, this Metrics Block MUST be discarded.
RFC6792]: I=10: Interval Duration - the reported value applies to the most recent measurement interval duration between successive metrics reports. I=11: Cumulative Duration - the reported value applies to the accumulation period characteristic of cumulative measurements. I=01: Sampled Value - the reported value is a sampled instantaneous value. I=00: Reserved In this document, MOS Metrics MAY be reported for intervals or for the duration of the media stream (cumulative). The value I=01, indicating a sampled value, MUST NOT be sent and MUST be discarded when received.
Reserved: 6 bits This field is reserved for future definition. In the absence of such a definition, the bits in this field MUST be set to zero and ignored by the receiver (see RFC 6709, Section 4.2). Block Length: 16 bits The length of this report block in 32-bit words, minus one. For the MOS Metrics Block, the block length is variable length. SSRC of source: 32 bits As defined in Section 4.1 of [RFC3611]. Segment i: 32 bits There are two segment types defined in this document: single- channel audio/video per SSRC segment and multi-channel audio per SSRC segment. Multi-channel audio per SSRC segment is used to deal with the case where multi-channel audio streams are carried in one RTP stream while a single-channel audio/video per SSRC segment is used to deal with the case where each media stream is identified by SSRC and sent in separate RTP streams. The leftmost bit of the segment determines its type. If the leftmost bit of the segment is zero, then it is a single-channel segment. If the leftmost bit is one, then it is a multi-channel audio segment. Note that two segment types cannot be present in the same metric block.
required to report the MOS value corresponding to each media stream using single-channel audio/video per SSRC segment in the same RTCP XR packet. Calculation Algorithm ID (CAID) : 8 bits The 8-bit CAID is the session specific reference to the calculation algorithm and associated qualifiers indicated in SDP (see Section 4.1) and used to compute the MOS score for this segment. Payload Type (PT): 7 bits MOS Metrics reporting depends on the payload format in use. This field identifies the RTP payload type in use during the reporting interval. The binding between RTP payload types and RTP payload formats is configured via a signaling protocol, for example, an SDP offer/answer exchange. If the RTP payload type used is changed during an RTP session, separate reports SHOULD be sent for each RTP payload type, with corresponding measurement information blocks indicating the time period to which they relate. Note that the use of this Report Block with MPEG Transport streams carried over RTP is undefined as each MPEG Transport stream may use distinct audio or video codecs and the indication of the encoding of these is within the MPEG Transport stream and does not use RTP payloads. MOS Value: 16 bits The estimated mean opinion score (MOS) for multimedia application performance is estimated using an algorithm that includes the impact of delay, loss, jitter and other impairments that affect media quality. This is an unsigned fixed-point 7:9 value representing the MOS, allowing the MOS score up to 127 in the integer part. MOS ranges are defined as part of the specification of the MOS estimation algorithm (Calculation Algorithm in this document), and are normally ranges like 1-5, 0-10, or 0-100. Two values are reserved: a value of 0xFFFE indicates that the measurement is out of range and a value of 0xFFFF indicates that the measurement is unavailable. Values outside of the range defined by the Calculation Algorithm, other than the two reserved values, MUST NOT be sent and MUST be ignored by the receiving system.
Section 4.1) and used to compute the MOS score for this segment. Payload Type (PT): 7 bits As defined in Section 3.2.1 of this document Channel Identifier (CHID): 3 bits If multiple channels of audio are carried in one RTP stream, each channel of audio will be viewed as an independent channel (e.g., left channel audio, right channel audio). This field is used to identify each channel carried in the same media stream. The default channel mapping follows static ordering rule described in Section 4.1 of [RFC3551]. However, there are some payload formats that use different channel mappings, e.g., AC-3 audio over RTP [RFC4184] only follow AC-3 channel order scheme defined in [ATSC]. Enhanced AC-3 audio over RTP [RFC4598] uses a dynamic channel transform mechanism. In order for the appropriate channel mapping to be determined, MOS metrics reports need to be tied to an RTP payload format. The reports should include the payload type of the reported media according to [RFC6792], so that it can be used to determine the appropriate channel mapping. MOS Value: 13 bits The estimated MOS for multimedia application performance is defined as including the effects of delay, loss, discard, jitter and other effects that would affect media quality. This is an unsigned fixed-point 7:6 value representing the MOS, allowing the MOS score up to 127 in the integer part. MOS ranges are defined as part of the specification of the MOS estimation algorithm
(Calculation Algorithm in this document), and are normally ranges like 1-5, 0-10, or 0-100. Two values are reserved: a value of 0x1FFE indicates out of range and a value of 0x1FFF indicates that the measurement is unavailable. Values outside of the range defined by the Calculation Algorithm, other than the two reserved values, MUST NOT be sent and MUST be ignored by the receiving system. RFC3611] defines the use of SDP [RFC4566] for signaling the use of XR blocks. However, XR blocks MAY be used without prior signaling (see Section 5 of RFC 3611). RFC4566] attribute "rtcp-xr" defined in [RFC3611] by providing an additional value of "xr-format" to signal the use of the report block defined in this document. Within the "xr-format", the syntax element "calgextmap" is an attribute as defined in [RFC4566] and used to signal the mapping of the local identifier (CAID) in the segment extension defined in Section 3.2 to the calculation algorithm. Specific extension attributes are defined by the specification that defines a specific extension name: there might be several. The ABNF [RFC5234] syntax is as follows.
xr-format =/ xr-mos-block xr-mos-block = "mos-metric" ["=" calgextmap *("," calgextmap)] calgextmap = mapentry "=" extensionname [SP extentionattributes] direction = "sendonly" / "recvonly" / "sendrecv" / "inactive" mapentry = "calg:" 1*3DIGIT [ "/" direction ] ; Values in the range 1-255 are valid ; if needed, 0 can be used to indicate that ; an algorithm is rejected extensionname = "P564";ITU-T P.564 Compliant Algorithm [P.564] / "G107";ITU-T G.107 [G.107] / "G107_1";ITU-T G.107.1 [G.107.1] / "TS101_329";ETSI TS 101 329-5 Annex E [ ETSI] /"JJ201_1 ";TTC JJ201.1 [TTC] /"P1201_1";ITU-T P.1201.2 [P.1201.1] /"P1201_2";ITU-T P.1201.2 [P.1201.2] /"P1202_1";ITU-T P.1202.1 [P.1202.1] /"P1202_2";ITU-T P.1202.2 [P.1202.2] /"P.862.2";ITU-T P.862.2 [P.862.2] /"P.863"; ITU-T P.863 [P.863] / non-ws-string extensionattributes = mosref /attributes-ext mosref = "mosref=" ("l"; lower resolution /"m"; middle resolution / "h";higher resolution / non-ws-string) attributes-ext = non-ws-string SP = <Defined in RFC 5234> non-ws-string = 1*(%x21-FF) Each local identifier (CAID) of calculation algorithm used in the segment defined in Section 3.2 is mapped to a string using an attribute of the form: a=calg:<value> [ "/"<direction> ] <name> [<extensionattributes>] where <name> is a calculation algorithm name, as above, <value> is the local identifier (CAID) of the calculation algorithm associated with the segment defined in this document and is an integer in the valid range, inclusive. Example: a=rtcp-xr:mos-metric=calg:1=G107,calg:2=P1202_1 A usable mapping MUST use IDs in the valid range, and each ID in this range MUST be unique and used only once for each stream or each channel in the stream.
The mapping MUST be provided per media stream (in the media-level section(s) of SDP, i.e., after an "m=" line). The syntax element "mosref" is referred to the media resolution relative reference and has three values 'l','m','h'. (e.g., narrowband (3.4 kHz) speech and Standard Definition (SD) or lower resolution video have 'l' resolution, super-wideband (>14 kHz) speech or higher and High Definition (HD) or higher resolution video have 'h' resolution, wideband speech (7 kHz) and video with resolution between SD and HD has 'm' resolution). The MOS reported in the MOS metrics block might vary with the MOS reference; for example, MOS values for narrowband, wideband, super-wideband codecs occupy the same range but SHOULD be reported in different value. For video application, MOS scores for SD resolution, HD resolution video also occupy the same ranges and SHOULD be reported in different value. RFC3611] applies. In the offer/answer context, the signaling described above might be used in three ways: o asymmetric behavior (segment extensions sent in only one direction), o the offer of mutually exclusive alternatives, or o the offer of more segments than can be sent in a single session. A direction attribute MAY be included in a "calgextmap"; without it, the direction implicitly inherits, of course, from the RTCP stream direction. Segment extensions, with their directions, MAY be signaled for an "inactive" stream. An extension direction MUST be compatible with the stream direction. If a segment extension in the SDP offer is marked as "sendonly" and the answerer desires to receive it, the extension MUST be marked as "recvonly" in the SDP answer. An answerer that has no desire to receive the extension or does not understand the extension SHOULD NOT include it in the SDP answer. If a segment extension is marked as "recvonly" in the SDP offer and the answerer desires to send it, the extension MUST be marked as "sendonly" in the SDP answer. An answerer that has no desire to, or is unable to, send the extension SHOULD NOT include it in the SDP answer.
If a segment extension is offered as "sendrecv", explicitly or implicitly, and asymmetric behavior is desired, the SDP MAY be modified to modify or add direction qualifiers for that segment extension. A "mosref" attribute and "MOS Type" attribute MAY be included in a calgextmap; if not present, the "mosref" and "MOS Type" MUST be as defined in the QoE estimation algorithm referenced by the name attribute (e.g., P.1201.1 [P.1201.1] indicates lower resolution used while P.1201.2 [P.1201.2] indicates higher resolution used) or payload type carried in the segment extension (e.g., EVRC-WB [RFC5188] indicates using Wideband Codec). However, not all payload types or MOS algorithm names indicate resolution to be used and MOS type to be used. If an answerer receives an offer with a "mosref" attribute value it doesn't support (e.g.,the answerer only supports "l" and receives "h" from offerer), the answer SHOULD reject the mosref attribute value offered by the offerer. If the answerer wishes to reject a "mosref" attribute offered by the offerer, it sets identifiers associated with segment extensions in the answer to the value in the range 4096-4351. The rejected answer MUST contain a "mosref" attribute whose value is the value of the SDP offer. Local identifiers in the valid range (inclusive) in an offer or answer must not be used more than once per media section. A session update MAY change the direction qualifiers of segment extensions under use. A session update MAY add or remove segment extension(s). Identifier values in the valid range MUST NOT be altered (remapped). If a party wishes to offer mutually exclusive alternatives, then multiple segment extensions with the same identifier in the (unusable) range 4096-4351 MAY be offered; the answerer SHOULD select at most one of the offered extensions with the same identifier, and remap it to a free identifier in the valid range for that extension to be usable. Note that the two segment types defined in Section 3 are also exclusive alternatives. If more segment extensions are offered in the valid range, the answerer SHOULD choose those that are desired and place the offered identifier value "as is" in the SDP answer. Similarly, if more segment extensions are offered than can be fit in the valid range, identifiers in the range 4096-4351 MAY be offered; the answerer SHOULD choose those that are desired and remap them to a free identifier in the valid range.
Note that the range 4096-4351 for these negotiation identifiers is deliberately restricted to allow expansion of the range of valid identifiers in the future. Segment extensions with an identifier outside the valid range cannot, of course, be used. Example: Note - port numbers, RTP profiles, payload IDs and rtpmaps, etc., have all been omitted for brevity. The offer: a=rtcp-xr:mos-metric=calg:4906=P1201_l,calg:4906=P1202_l, calg: 4907=G107 The answerer is interested in transmission P.1202.1 on a lower resolution application, but it doesn't support P.1201.1 on a lower resolution application at all. It is interested in transmission G.107. Therefore, it adjusts the declarations: a=rtcp-xr:mos-metric=calg:1=P1202_l,calg:2=G107 RFC3611]. RFC4566] for an SDP attribute. o contact name, email address: RAI Area Directors <firstname.lastname@example.org>
o attribute name (as it will appear in SDP): calgextmap o long-form attribute name in English: calculation algorithm map definition o type of attribute (session level, media level, or both): both o whether the attribute value is subject to the charset attribute: not subject to the charset attribute o a one-paragraph explanation of the purpose of the attribute: This attribute defines the mapping from the local identifier (CAID) in the segment extension defined in Section 3.2 into the calculation algorithm name as documented in specifications and appropriately registered. o a specification of appropriate attribute values for this attribute: see RFC 7266. Section 4.1 of [RFC5226]. o Entries in the registry are identified by entry name and mapped to the local identifier (CAID) in the segment extension defined in Section 3.2. o Registration Template The following information must be provided with each registration: * Name: A string uniquely and unambiguously identifying the calculation algorithm for use in protocols.
* Name Description: A valid Description of the calculation algorithm Name. * Reference: The reference that defines the calculation algorithm corresponding to the Name and Name Description. * Type: The media type to which the calculation algorithm is applied o Initial assignments are as follows: Name Name Description Reference Type ========= ================================ ========== ==== P564 ITU-T P.564 Compliant Algorithm [P.564] voice G107 ITU-T G.107 [G.107] voice TS101_329 ETSI TS 101 329-5 Annex E [ETSI] voice JJ201_1 TTC JJ201.1 [TTC] voice G107_1 ITU-T G.107.1 [G.107.1] voice P862 ITU-T P.862 [P.862] voice P862_2 ITU-T P.862.2 [P.862.2] voice P863 ITU-T P.863 [P.863] voice P1201_1 ITU-T P.1201.1 [P.1201.1] multimedia P1201_2 ITU-T P.1201.2 [P.1201.2] multimedia P1202_1 ITU-T P.1202.1 [P.1202.1] video P1202_2 ITU-T P.1202.2 [P.1202.2] video RFC3611].
[ATSC] Advanced Television Systems Committee, Inc., "Digital Audio Compression Standard (AC-3, E-AC-3) Revision B", ATSC Document A/52B, June 2005. [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. [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", STD 65, RFC 3551, July 2003. [RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed., "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, November 2003. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. [RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC6776] Clark, A. and Q. Wu, "Measurement Identity and Information Reporting Using a Source Description (SDES) Item and an RTCP Extended Report (XR) Block", RFC 6776, October 2012. [BS.1387-1] ITU-R, "Method for objective measurements of perceived audio quality", ITU-R Recommendation BS.1387-1, 1998-2001. [ETSI] ETSI, "TIPHON Release 3; Technology Compliance Specification; Part 5: Quality of Service (QoS) measurement methodologies", ETSI TS 101 329-5 V1.1.1, November 2000. [G.107] ITU-T, "The E Model, a computational model for use in transmission planning", ITU-T Recommendation G.107, February 2014. [G.107.1] ITU-T, "Wideband E-model", ITU-T Recommendation G.107.1, December 2011. [G.1082] ITU-T, "Measurement-based methods for improving the robustness of IPTV performance", ITU-T Recommendation G.1082, April 2009. [P.1201.1] ITU-T, "Parametric non-intrusive assessment of audiovisual media streaming quality - Lower resolution application area", ITU-T Recommendation P.1201.1, October 2012. [P.1201.2] ITU-T, "Parametric non-intrusive assessment of audiovisual media streaming quality - Higher resolution application area", ITU-T Recommendation P.1201.2, October 2012. [P.1202.1] ITU-T, "Parametric non-intrusive bitstream assessment of video media streaming quality - Lower resolution application area", ITU-T Recommendation P.1202.1, October 2012. [P.1202.2] ITU-T, "Parametric non-intrusive bitstream assessment of video media streaming quality - Higher resolution application area", ITU-T Recommendation P.1202.2, May 2013.
[P.564] ITU-T, "Conformance testing for narrowband Voice over IP transmission quality assessment models", ITU-T Recommendation P.564, November 2007. [P.862] ITU-T, "Perceptual evaluation of speech quality (PESQ): An objective method for end-to-end speech quality assessment of narrow-band telephone networks and speech codecs", ITU-T Recommendation P.862, February 2001. [P.862.1] ITU-T, "Mapping function for transforming P.862 raw result scores to MOS-LQO", ITU-T Recommendation P.862.1, November 2003. [P.862.2] ITU-T, "Wideband extension to Recommendation P.862 for the assessment of wideband telephone networks and speech codecs", ITU-T Recommendation P.862.2, November 2007. [P.863] ITU-T, "Perceptual objective listening quality assessment", ITU-T Recommendation P.863, January 2011. [RFC4184] Link, B., Hager, T., and J. Flaks, "RTP Payload Format for AC-3 Audio", RFC 4184, October 2005. [RFC4598] Link, B., "Real-time Transport Protocol (RTP) Payload Format for Enhanced AC-3 (E-AC-3) Audio", RFC 4598, July 2006. [RFC5188] Desineni, H. and Q. Xie, "RTP Payload Format for the Enhanced Variable Rate Wideband Codec (EVRC-WB) and the Media Subtype Updates for EVRC-B Codec", RFC 5188, February 2008. [RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New Performance Metric Development", BCP 170, RFC 6390, October 2011. [RFC6792] Wu, Q., Ed., Hunt, G., and P. Arden, "Guidelines for Use of the RTP Monitoring Framework", RFC 6792, November 2012. [TTC] Telecommunication Technology Committee, "A Method for Speech Quality Assessment for IP Telephony", TTC JJ-201.01 (Japan), November 2013, <http://www.ttc.or.jp/jp/document_list/pdf/j/STD/ JJ-201.01v7.pdf>.
Section 3.2.1, MOS value definition. * Units of Measurement: See Section 3.2.1, MOS value definition. * Measurement Point(s) with Potential Measurement Domain: See Section 3, second paragraph. * Measurement Timing: See Section 3, third paragraph for measurement timing and Section 3.1 for Interval Metric flag. * Use and applications: See Section 1.4. * Reporting model: See RFC 3611. b. Segment Type Metric * Metric Name: Segment Type in RTP * Metric Description: It is used to identify the segment type of RTP stream used in this report block. For more details, see Section 3.2.1, Segment type definition. * Method of Measurement or Calculation: See Section 3.2.1, Segment Type definition. * Units of Measurement: See Section 3.2.1, Segment Type definition. * Measurement Point(s) with Potential Measurement Domain: See Section 3, second paragraph. * Measurement Timing: See Section 3, third paragraph for measurement timing and Section 3.1 for Interval Metric flag. * Use and applications: See Section 1.4.
* Reporting model: See RFC 3611. c. Calculation Algorithm Identifier Metric * Metric Name: RTP Stream Calculation Algorithm Identifier * Metric Description: It is the local identifier of RTP Stream calculation Algorithm associated with this segment in the range 1-255 (inclusive). * Method of Measurement or Calculation: See Section 3.2.1, Calculation Algorithm ID definition. * Units of Measurement: See Section 3.2.1, Calg Algorithm ID definition. * Measurement Point(s) with Potential Measurement Domain: See Section 3, second paragraph. * Measurement Timing: See Section 3, third paragraph for measurement timing and Section 3.1 for Interval Metric flag. * Use and applications: See Section 1.4. * Reporting model: See RFC 3611. d. Payload Type Metric * Metric Name: RTP Payload Type * Metric Description: It is used to identify the format of the RTP payload. For more details, see Section 3.2.1, payload type definition. * Method of Measurement or Calculation: See Section 3.2.1, Payload type definition. * Units of Measurement: See Section 3.2.1, Payload type definition. * Measurement Point(s) with Potential Measurement Domain: See Section 3, second paragraph. * Measurement Timing: See Section 3, third paragraph for measurement timing and Section 3.1 for Interval Metric flag. * Use and applications: See Section 1.4.
* Reporting model: See RFC 3611. e. Channel Identifier Metric * Metric Name: Audio Channel Identifier in RTP * Metric Description: It is used to identify each audio channel carried in the same RTP stream. For more details, see Section 3.2.2, channel identifier definition. * Method of Measurement or Calculation: See Section 3.2.2, Channel Identifier definition. * Units of Measurement: See Section 3.2.2, Channel Identifier definition. * Measurement Point(s) with Potential Measurement Domain: See Section 3, second paragraph. * Measurement Timing: See Section 3, third paragraph for measurement timing and Section 3.1 for Interval Metric flag. * Use and applications: See Section 1.4. * Reporting model: See RFC 3611.