





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.
















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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







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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



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   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.



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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.







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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.



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   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



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      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.







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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



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      (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.


























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   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.




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   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.





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   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.





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   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>




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   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.




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      *  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>







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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.







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   [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.





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   [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>.






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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.




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      *  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.




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      *  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.


























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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













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