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rfc:rfc7266

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

Abstract

 This 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.

Clark, et al. Standards Track [Page 1] RFC 7266 RTCP XR MOS Report Blocks June 2014

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.

Table of Contents

 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

Clark, et al. Standards Track [Page 2] RFC 7266 RTCP XR MOS Report Blocks June 2014

1. Introduction

1.1. MOS Metrics Report Block

 This document defines a new block type to augment those defined in
 [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].

1.2. RTCP and RTCP XR Reports

 The use of RTCP for reporting is defined in [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].

1.3. Performance Metrics Framework

 The Performance Metrics Framework [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].

1.4. Applicability

 The MOS Metrics Report Block can be used in any application of RTP
 for which QoE (Quality-of-Experience) measurement algorithms are
 defined.
 The factors that affect real-time audio/video application quality can
 be split into two categories.  The first category consists of
 transport-specific factors such as packet loss, delay, and jitter
 (which also translates into losses in the playback buffer).  The
 factors in the second category consists of content- and codec-related
 factors such as codec type and loss recovery technique, coding bit
 rate, packetization scheme, and content characteristics
 Transport-specific factors may be insufficient to infer real-time
 media quality as codec related parameters and the interaction between
 transport problems and application-layer protocols can have a
 substantial effect on observed media quality.  Media quality may be
 measured using algorithms that directly compare input and output

Clark, et al. Standards Track [Page 3] RFC 7266 RTCP XR MOS Report Blocks June 2014

 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.

2. Terminology

2.1. Standards Language

 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].
 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.

Clark, et al. Standards Track [Page 4] RFC 7266 RTCP XR MOS Report Blocks June 2014

3. MOS Metrics Block

 A multimedia application MOS Metric is commonly expressed as a MOS.
 The MOS is usually on a scale from 1 to 5, in which 5 represents
 excellent and 1 represents unacceptable; however, it can use other
 ranges (for example, 0 to 10 ).  The term "MOS" originates from
 subjective testing and is used to refer to the mean of a number of
 individual opinion scores.  Therefore, there is a well-understood
 relationship between MOS and user experience; hence, the industry
 commonly uses MOS as the scale for objective test results.
 Subjective tests can be used for measuring live network traffic;
 however, the use of objective or algorithmic measurement techniques
 allows much larger scale measurements to be made.  Within the scope
 of this document, mean opinion scores are obtained using objective or
 estimation algorithms.  ITU-T or ITU-R recommendations (e.g.,
 [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.

Clark, et al. Standards Track [Page 5] RFC 7266 RTCP XR MOS Report Blocks June 2014

3.1. Report Block Structure

 The MOS Metrics 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=29     | I |  Reserved |       Block Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        SSRC of source                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Segment  1                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Segment 2                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ..................
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Segment n                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.2. Definition of Fields in MOS Metrics Block

 Block type (BT): 8 bits
    The MOS Metrics Block is identified by the constant 29.
 Interval Metric flag (I): 2 bits
    This field is used to indicate whether the MOS Metrics are
    Sampled, Interval, or Cumulative [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.

Clark, et al. Standards Track [Page 6] RFC 7266 RTCP XR MOS Report Blocks June 2014

 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.

3.2.1. Single-Channel Audio/Video per SSRC Segment

 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |S|     CAID      |    PT       |           MOS Value           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Segment Type (S): 1 bit
    This field is used to identify the segment type used in this
    report block.  A zero identifies this as a single-channel
    audio/video per SSRC segment.  Single channel means there is only
    one media stream carried in one RTP stream.  The single-channel
    audio/video per SSRC segment can be used to report the MOS value
    associated with the media stream identified by SSRC.  If there are
    multiple media streams and they want to use the single-channel
    audio/video per SSRC segment to report the MOS value, they should
    be carried in the separate RTP streams with each identified by
    different SSRC.  In this case, multiple MOS Metrics Blocks are

Clark, et al. Standards Track [Page 7] RFC 7266 RTCP XR MOS Report Blocks June 2014

    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.

Clark, et al. Standards Track [Page 8] RFC 7266 RTCP XR MOS Report Blocks June 2014

3.2.2. Multi-Channel Audio per SSRC Segment

 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |S|     CAID      |    PT       |CHID |        MOS Value        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Segment Type (S): 1 bit
    This field is used to identify the segment type used in this
    report block.  A one identifies this as a multi-channel audio
    segment.
 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
    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

Clark, et al. Standards Track [Page 9] RFC 7266 RTCP XR MOS Report Blocks June 2014

    (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.

4. SDP Signaling

 [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).

4.1. SDP "rtcp-xr-attrib" Attribute Extension

 This section augments the SDP [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.

Clark, et al. Standards Track [Page 10] RFC 7266 RTCP XR MOS Report Blocks June 2014

 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.

Clark, et al. Standards Track [Page 11] RFC 7266 RTCP XR MOS Report Blocks June 2014

 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.

4.2. Offer/Answer Usage

 When SDP is used in offer/answer context, the SDP Offer/Answer usage
 defined in [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.

Clark, et al. Standards Track [Page 12] RFC 7266 RTCP XR MOS Report Blocks June 2014

 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.

Clark, et al. Standards Track [Page 13] RFC 7266 RTCP XR MOS Report Blocks June 2014

 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

5. 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].

5.1. New RTCP XR Block Type Value

 This document assigns the block type value 29 in the IANA "RTP
 Control Protocol Extended Reports (RTCP XR) Block Type Registry" to
 the "MOS Metrics Block".

5.2. New RTCP XR SDP Parameter

 This document also registers a new parameter "mos-metric" in the "RTP
 Control Protocol Extended Reports (RTCP XR) Session Description
 Protocol (SDP) Parameters Registry".

5.3. The SDP "calgextmap" Attribute

 This section contains the information required by [RFC4566] for an
 SDP attribute.
 o  contact name, email address: RAI Area Directors
    <rai-ads@tools.ietf.org>

Clark, et al. Standards Track [Page 14] RFC 7266 RTCP XR MOS Report Blocks June 2014

 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.

5.4. New Registry of Calculation Algorithms

 This document creates a new registry called "RTCP XR MOS Metric block
 - multimedia application Calculation Algorithm" as a subregistry of
 the "RTP Control Protocol Extended Reports (RTCP XR) Block Type
 Registry".  This registry applies to the multimedia session where
 each type of medium is sent in a separate RTP stream and also applies
 to the session where multi-channel audios are carried in one RTP
 stream.  Policies for this new registry are as follows:
 o  The information required to support this assignment is an
    unambiguous definition of the new metric, covering the base
    measurements and how they are processed to generate the reported
    metric.
 o  The review process for the registry is "Specification Required" as
    described in 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.

Clark, et al. Standards Track [Page 15] RFC 7266 RTCP XR MOS Report Blocks June 2014

  • 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

6. Security Considerations

 The new RTCP XR blocks proposed in this document introduce no new
 security considerations beyond those described in [RFC3611].

7. Contributors

 This document merges ideas from two documents addressing the MOS
 Metric Reporting issue.  The authors of these documents are listed
 below (in alphabetical order):
    Alan Clark <alan.d.clark@telchemy.com>
    Geoff Hunt <r.geoff.hunt@gmail.com>
    Martin Kastner <martin.kastner@telchemy.com>
    Kai Lee <leekai@ctbri.com.cn>
    Roland Schott <roland.schott@telekom.de>
    Qin Wu <sunseawq@huawei.com>
    Glen Zorn <gwz@net-zen.net>

Clark, et al. Standards Track [Page 16] RFC 7266 RTCP XR MOS Report Blocks June 2014

8. Acknowledgements

 The authors gratefully acknowledge the comments and contributions
 made by Bruce Adams, Philip Arden, Amit Arora, Bob Biskner, Kevin
 Connor, Claus Dahm, Randy Ethier, Roni Even, Jim Frauenthal, Albert
 Higashi, Tom Hock, Shane Holthaus, Paul Jones, Rajesh Kumar, Keith
 Lantz, Mohamed Mostafa, Amy Pendleton, Colin Perkins, Mike Ramalho,
 Ravi Raviraj, Albrecht Schwarz, Tom Taylor, Bill Ver Steeg, David R.
 Oran, Ted Lemon, Benoit Claise, Pete Resnick, Ali Begen, and Hideaki
 Yamada.

9. References

9.1. Normative References

 [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.

Clark, et al. Standards Track [Page 17] RFC 7266 RTCP XR MOS Report Blocks June 2014

 [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.

9.2. Informative References

 [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.

Clark, et al. Standards Track [Page 18] RFC 7266 RTCP XR MOS Report Blocks June 2014

 [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>.

Clark, et al. Standards Track [Page 19] RFC 7266 RTCP XR MOS Report Blocks June 2014

Appendix A. Metrics Represented Using the Template from RFC 6390

 a.  MOS Value Metric
  • Metric Name: MOS in RTP
  • Metric Description: The estimated mean opinion score for

multimedia application performance of the RTP stream is defined

       as including the effects of delay, loss, discard, jitter, and
       others on audio or video quality.
  • Method of Measurement or Calculation: See 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.

Clark, et al. Standards Track [Page 20] RFC 7266 RTCP XR MOS Report Blocks June 2014

  • 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.

Clark, et al. Standards Track [Page 21] RFC 7266 RTCP XR MOS Report Blocks June 2014

  • 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.

Clark, et al. Standards Track [Page 22] RFC 7266 RTCP XR MOS Report Blocks June 2014

Authors' Addresses

 Alan Clark
 Telchemy Incorporated
 2905 Premiere Parkway, Suite 280
 Duluth, GA  30097
 USA
 EMail: alan.d.clark@telchemy.com
 Qin Wu
 Huawei
 101 Software Avenue, Yuhua District
 Nanjing, Jiangsu  210012
 China
 EMail: sunseawq@huawei.com
 Roland Schott
 Deutsche Telekom
 Heinrich-Hertz-Strasse 3-7
 Darmstadt  64295
 Germany
 EMail: Roland.Schott@telekom.de
 Glen Zorn
 Network Zen
 77/440 Soi Phoomjit, Rama IV Road
 Phra Khanong, Khlong Toie
 Bangkok  10110
 Thailand
 Phone: +66 (0) 87 502 4274
 EMail: gwz@net-zen.net

Clark, et al. Standards Track [Page 23]

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