Internet Engineering Task Force (IETF) A. Clark

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
<[email protected]>

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 <[email protected]>
Geoff Hunt <[email protected]>
Martin Kastner <[email protected]>
Kai Lee <[email protected]>
Roland Schott <[email protected]>
Qin Wu <[email protected]>
Glen Zorn <[email protected]>

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: [email protected]

Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China

EMail: [email protected]

Roland Schott
Deutsche Telekom
Heinrich-Hertz-Strasse 3-7
Darmstadt 64295
Germany

EMail: [email protected]

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: [email protected]

Clark, et al. Standards Track [Page 23]