Internet Engineering Task Force (IETF) S. Nandakumar
Request for Comments: 8859 Cisco
Category: Standards Track January 2021
ISSN: 2070-1721
A Framework for Session Description Protocol (SDP) Attributes When
Multiplexing
Abstract
The purpose of this specification is to provide a framework for
analyzing the multiplexing characteristics of Session Description
Protocol (SDP) attributes when SDP is used to negotiate the usage of
a single 5-tuple for sending and receiving media associated with
multiple media descriptions.
This specification also categorizes the existing SDP attributes based
on the framework described herein.
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 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8859.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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described in the Simplified BSD License.
Table of Contents
1. Introduction
2. Terminology
3. Motivation
4. SDP Attribute Analysis Framework
4.1. Category: NORMAL
4.2. Category: CAUTION
4.3. Category: IDENTICAL
4.4. Category: SUM
4.5. Category: TRANSPORT
4.6. Category: INHERIT
4.7. Category: IDENTICAL-PER-PT
4.8. Category: SPECIAL
4.9. Category: TBD
5. Analysis of Existing Attributes
5.1. RFC 4566: SDP
5.2. RFC 4585: RTP/AVPF
5.3. RFC 5761: Multiplexing RTP and RTCP
5.4. RFC 3312: Integration of Resource Management and SIP
5.5. RFC 4574: SDP "label" Attribute
5.6. RFC 5432: QoS Mechanism Selection in SDP
5.7. RFC 4568: SDP Security Descriptions
5.8. RFC 5762: RTP over DCCP
5.9. RFC 6773: DCCP-UDP Encapsulation
5.10. RFC 5506: Reduced-Size RTCP in RTP Profile
5.11. RFC 6787: Media Resource Control Protocol Version 2
5.12. RFC 8445: ICE
5.13. RFC 5285: RTP Header Extensions
5.14. RFC 3605: RTCP Attribute in SDP
5.15. RFC 5576: Source-Specific SDP Attributes
5.16. RFC 7273: RTP Clock Source Signaling
5.17. RFC 6236: Image Attributes in SDP
5.18. RFC 7197: Duplication Delay Attribute in SDP
5.19. RFC 7266: RTCP XR Blocks for MOS Metric Reporting
5.20. RFC 6285: Rapid Acquisition of Multicast RTP Sessions
5.21. RFC 6230: Media Control Channel Framework
5.22. RFC 6364: SDP Elements for FEC Framework
5.23. RFC 4796: "content" Attribute
5.24. RFC 3407: SDP Simple Capability Declaration
5.25. RFC 6284: Port Mapping between Unicast and Multicast RTP
Sessions
5.26. RFC 6714: MSRP-CEMA
5.27. RFC 4583: SDP Format for BFCP Streams
5.28. RFC 5547: SDP Offer/Answer for File Transfer
5.29. RFC 6849: SDP and RTP Media Loopback Extension
5.30. RFC 5760: RTCP with Unicast Feedback
5.31. RFC 3611: RTCP XR
5.32. RFC 5939: SDP Capability Negotiation
5.33. RFC 6871: SDP Media Capabilities Negotiation
5.34. RFC 7006: Miscellaneous Capabilities Negotiation in SDP
5.35. RFC 4567: Key Management Extensions for SDP and RTSP
5.36. RFC 4572: Comedia over TLS in SDP
5.37. RFC 4570: SDP Source Filters
5.38. RFC 6128: RTCP Port for Multicast Sessions
5.39. RFC 6189: ZRTP
5.40. RFC 4145: Connection-Oriented Media
5.41. RFC 6947: The SDP "altc" Attribute
5.42. RFC 7195: SDP Extension for Circuit-Switched Bearers in
PSTN
5.43. RFC 7272: IDMS Using the RTP Control Protocol (RTCP)
5.44. RFC 5159: Open Mobile Alliance (OMA) Broadcast (BCAST) SDP
Attributes
5.45. RFC 6193: Media Description for IKE in SDP
5.46. RFC 2326: Real Time Streaming Protocol
5.47. RFC 7826: Real-Time Streaming Protocol
5.48. RFC 6064: SDP and RTSP Extensions for 3GPP
5.49. RFC 3108: ATM SDP
5.50. 3GPP TS 183.063
5.51. 3GPP TS 24.229
5.52. ITU T.38
5.53. ITU-T Q.1970
5.54. ITU-T H.248.15
5.55. RFC 4975: The Message Session Relay Protocol
5.56. Historical Attributes
6. bwtype Attribute Analysis
6.1. RFC 4566: SDP
6.2. RFC 3556: SDP Bandwidth Modifiers for RTCP Bandwidth
6.3. RFC 3890: Bandwidth Modifier for SDP
7. rtcp-fb Attribute Analysis
7.1. RFC 4585: RTP/AVPF
7.2. RFC 5104: Codec Control Messages in AVPF
7.3. RFC 6285: Unicast-Based Rapid Acquisition of Multicast RTP
Sessions (RAMS)
7.4. RFC 6679: ECN for RTP over UDP/IP
7.5. RFC 6642: Third-Party Loss Report
7.6. RFC 5104: Codec Control Messages in AVPF
8. group Attribute Analysis
8.1. RFC 5888: SDP Grouping Framework
8.2. RFC 3524: Mapping Media Streams to Resource Reservation
Flows
8.3. RFC 4091: ANAT Semantics
8.4. RFC 5956: FEC Grouping Semantics in SDP
8.5. RFC 5583: Signaling Media Decoding Dependency in SDP
8.6. RFC 7104: Duplication Grouping Semantics in the SDP
9. ssrc-group Attribute Analysis
9.1. RFC 5576: Source-Specific SDP Attributes
9.2. RFC 7104: Duplication Grouping Semantics in the SDP
10. QoS Mechanism Token Analysis
10.1. RFC 5432: QoS Mechanism Selection in SDP
11. k= Attribute Analysis
11.1. RFC 4566: SDP
12. content Attribute Analysis
12.1. RFC 4796
12.2. 3GPP TS 24.182
12.3. 3GPP TS 24.183
13. Payload Formats
13.1. RFC 5109: RTP Payload Format for Generic FEC
14. Multiplexing Considerations for Encapsulating Attributes
14.1. RFC 3407: cpar Attribute Analysis
14.2. RFC 5939 Analysis
14.2.1. Recommendation: Procedures for Potential Configuration
Pairing
14.3. RFC 6871 Analysis
14.3.1. Recommendation: Dealing with Payload Type Numbers
14.3.2. Recommendation: Dealing with Latent Configurations
15. IANA Considerations
15.1. New "Multiplexing Categories" Subregistry
15.2. "Mux Category" Column for Subregistries
15.2.1. Table: SDP bwtype
15.2.2. Table: attribute-name
15.2.3. Table: content SDP Parameters
15.2.4. Table: Semantics for the "group" SDP Attribute
15.2.5. Table: "rtcp-fb" Attribute Values
15.2.6. Table: "ack" and "nack" Attribute Values
15.2.7. Table: "depend" SDP Attribute Values
15.2.8. Table: "cs-correlation" Attribute Values
15.2.9. Table: Semantics for the "ssrc-group" SDP Attribute
15.2.10. Table: SDP/RTSP Key Management Protocol Identifiers
15.2.11. Table: Codec Control Messages
15.2.12. Table: QoS Mechanism Tokens
15.2.13. Table: SDP Capability Negotiation Option Tags
15.2.14. Table: Timestamp Reference Clock Source Parameters
15.2.15. Table: Media Clock Source Parameters
16. Security Considerations
17. References
17.1. Normative References
17.2. Informative References
Acknowledgements
Author's Address
1. Introduction
SDP defines several attributes for capturing characteristics that
apply to the individual media descriptions (described by "m=" lines)
and the overall multimedia session. Typically, different media types
(audio, video, etc.) described using different media descriptions
represent separate RTP sessions that are carried over individual
transport-layer flows. However, [RFC8843] defines a way to use a
single address:port combination (BUNDLE address) for receiving media
associated with multiple SDP media descriptions. This would, for
example, allow the usage of a single set of Interactive Connectivity
Establishment (ICE) [RFC8445] candidates for multiple media
descriptions. This, in turn, has made it necessary to understand the
interpretation and usage of the SDP attributes defined for the
multiplexed media descriptions.
Given the number of SDP attributes registered with the [IANA] and the
possibility of new attributes being defined in the future, there is
need for a framework to analyze these attributes for their
applicability in the transport multiplexing use cases.
The document starts with providing the motivation for requiring such
a framework. This is followed by introduction to the SDP attribute
analysis framework and procedures, following which several sections
apply the framework to the SDP attributes registered with the [IANA].
2. Terminology
5-tuple: A collection of the following values: source address,
source port, destination address, destination port, and transport-
layer protocol.
3GPP: Third Generation Partnership Project; see
<https://www.3gpp.org> for more information about this
organization.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Motivation
An effort to reduce the number of necessary transport-level flows is
required because of the time and complications involved in setting up
Secure Real-time Transport Protocol (SRTP) [RFC5763] transports for
use by RTP based on ICE [RFC8445] and Datagram Transport Layer
Security (DTLS). These procedures motivate conservation of ports
bindings on the Network Address Translators (NATs). This necessity
has resulted in the definition of ways, such as that described in
[RFC8843], to multiplex RTP over a single transport flow in order to
preserve network resources such as port numbers. This imposes
further restrictions on applicability of the SDP attributes as they
are defined today.
The specific problem is that there are attribute combinations that
make sense when specified on independent "m=" lines -- as with
classical SDP -- that do not make sense when those "m=" lines are
then multiplexed over the same transport. To give an obvious
example, ICE permits each "m=" line to have an independently
specified "ice-ufrag" attribute. However, if the media from multiple
"m=" lines is multiplexed over the same ICE component, then the
meaning of media-level "ice-ufrag" attributes becomes muddled.
At the time of writing this document, there are close to 250 SDP
attributes registered with the [IANA], and more will be added in the
future. There is no clearly defined procedure to establish the
validity/applicability of these attributes when used with transport
multiplexing.
4. SDP Attribute Analysis Framework
Attributes in an SDP session description can be defined at the
session level, media level, or source level. Informally, there are
various semantic groupings for these attributes. One such grouping
could be as follows:
* Attributes related to media content such as media type, encoding
schemes, and payload types.
* Attributes specifying media transport characteristics such as RTP/
RTP Control Protocol (RTCP) port numbers, network addresses, and
QoS.
* Metadata description attributes capturing session timing and
origin information.
* Attributes establishing relationships between media descriptions,
such as grouping framework [RFC5888].
The proposed framework analyzes the SDP attributes usage under
multiplexing and assigns each SDP attribute to an appropriate
multiplexing category. Since the multiplexing categories defined in
this specification are independent of any informal semantic groupings
of the SDP attributes, the categorizations assigned are normative.
4.1. Category: NORMAL
The attributes in the NORMAL category can be independently specified
when multiplexed, and they retain their original semantics.
In the example given below, the direction and label attributes are
independently specified for audio and video "m=" lines. These
attributes are not impacted by multiplexing these media streams over
a single transport-layer flow.
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
m=audio 49172 RTP/AVP 99
a=sendonly
a=label:1
a=rtpmap:99 iLBC/8000
m=video 49172 RTP/AVP 31
a=recvonly
a=label:2
a=rtpmap:31 H261/90000
4.2. Category: CAUTION
It is not advisable to multiplex with the attributes in the CAUTION
category, since their usage under multiplexing might lead to
incorrect behavior.
Example: Multiplexing media descriptions over a single Datagram
Congestion Control Protocol (DCCP) transport [RFC5762] is not
recommended, since DCCP is a connection-oriented protocol and
therefore doesn't allow multiple connections on the same 5-tuple.
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=
c=IN IP4 client.biloxi.example.com
t=0 0
m=video 5004 DCCP/RTP/AVP 99
a=rtpmap:99 h261/9000
a=dccp-service-code:SC=x52545056
a=setup:passive
a=connection:new
m=video 5004 DCCP/RTP/AVP 100
a=rtpmap:100 h261/9000
a=dccp-service-code:SC=x5254504f
a=setup:passive
a=connection:new
4.3. Category: IDENTICAL
The attributes and their associated values (if any) in the IDENTICAL
category MUST be repeated across all the media descriptions under
multiplexing.
Attributes such as rtcp-mux fall into this category. Since RTCP
reporting is done per RTP session, RTCP multiplexing MUST be enabled
for both the audio and video "m=" lines if they are transported over
a single 5-tuple.
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=
c=IN IP4 client.biloxi.example.com
t=0 0
m=audio 34567 RTP/AVP 97
a=rtcp-mux
m=video 34567 RTP/AVP 31
a=rtpmap:31 H261/90000
a=rtcp-mux
Note: Even though IDENTICAL attributes must be repeated across all
media descriptions under multiplexing, they might not always be
explicitly encoded across all media descriptions. [RFC8843] defines
rules for when attributes and their values are implicitly applied to
media description.
4.4. Category: SUM
The attributes in the SUM category can be set as they are normally
used, but software using them in the multiplexing scenario MUST apply
the sum of all the attributes being multiplexed instead of trying to
use them independently. This is typically used for bandwidth or
other rate-limiting attributes to the underlying transport.
The software parsing the SDP sample below should use the aggregate
Application Specific (AS) bandwidth value from the individual media
descriptions to determine the AS value for the multiplexed session.
Thus the calculated AS value would be 256+64 kilobits per second for
the given example.
v=0
o=test 2890844526 2890842807 IN IP4 client.biloxi.example.com
c=IN IP4 client.biloxi.example.com
t=0 0
m=audio 49170 RTP/AVP 0
b=AS:64
m=video 51372 RTP/AVP 31
b=AS:256
4.5. Category: TRANSPORT
The attributes in the TRANSPORT category can be set normally for
multiple items in a multiplexed group, but the software MUST pick the
one that's associated with the "m=" line whose information is used
for setting up the underlying transport.
In the example below, the "a=crypto" attribute is defined for both
the audio and video "m=" lines. The video media line's "a=crypto"
attribute is chosen since its MID value (bar) appears first in the
"a=group:BUNDLE" line. This is due to the BUNDLE grouping semantic
[RFC8843], which mandates that the values from the "m=" line
corresponding to the mid appearing first on the "a=group:BUNDLE" line
be considered for setting up the RTP transport.
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
a=group:BUNDLE bar foo
m=audio 49172 RTP/AVP 99
a=mid:foo
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:d0RmdmcmVCspeEc3QGZiNWpVLFJhQX1cfHAwJSoj|2^20|1:32
a=rtpmap:99 iLBC/8000
m=video 51374 RTP/AVP 31
a=mid:bar
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:EcGZiNWpFJhQXdspcl1ekcmVCNWpVLcfHAwJSoj|2^20|1:32
a=rtpmap:96 H261/90000
4.6. Category: INHERIT
The attributes in the INHERIT category encapsulate other SDP
attributes or parameters. These attributes inherit their
multiplexing characteristics from the attributes or parameters they
encapsulate. Such attributes are defined in [RFC3407], [RFC5939],
and [RFC6871] as part of a generic framework for indicating and
negotiating capabilities in the SDP related to transport, media, and
media format.
The inheritance manifests itself when the encapsulated attribute or
parameter is being leveraged. In the case of SDP Capability
Negotiation [RFC5939], for example, this occurs when a capability
(encapsulating attribute) is used as part of a configuration; the
configuration inherits the multiplexing category of each of its
constituent (encapsulated) attributes and parameters. The inherited
attributes MUST be coherent in order to form a valid configuration
from a multiplexing point of view (see Section 14 for further
details).
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
m=video 3456 RTP/AVP 100
a=rtpmap:100 VP8/90000
a=fmtp:100 max-fr=30;max-fs=8040
a=sqn: 0
a=cdsc: 1 video RTP/AVP 100
a=cpar: a=rtcp-mux
m=video 3456 RTP/AVP 101
a=rtpmap:101 VP8/90000
a=fmtp:100 max-fr=15;max-fs=1200
a=cdsc: 2 video RTP/AVP 101
a=cpar: a=rtcp-mux
In this example, the category IDENTICAL is inherited by the cpar-
encapsulated "rtcp-mux" attribute.
4.7. Category: IDENTICAL-PER-PT
The attributes in the IDENTICAL-PER-PT category define the RTP
payload configuration on the basis of the payload type, and they MUST
have identical values across all the media descriptions for a given
RTP payload type when repeated. These payload types identify the
same codec configuration as defined in Section 9.1 of [RFC8843] under
this context.
In the SDP example below, Payload Types 96 and 97 are repeated across
all the video "m=" lines, and all the payload-specific parameters
(for example, rtpmap and fmtp) are identical. (Note: some line
breaks are due to formatting only.)
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
a=group:BUNDLE cam1 cam2
m=video 96 97
a=mid:cam1
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42400d; max-fs=3600; max-fps=3000;
max-mbps=108000; max-br=1000
a=rtpmap:97 H264/90000
a=fmtp:97 profile-level-id=42400a; max-fs=240; max-fps=3000;
max-mbps=7200; max-br=200
m=video 96 97
a=mid:cam2
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42400d; max-fs=3600; max-fps=3000;
max-mbps=108000; max-br=1000
a=rtpmap:97 H264/90000
a=fmtp:97 profile-level-id=42400a; max-fs=240; max-fps=3000;
max-mbps=7200; max-br=200
4.8. Category: SPECIAL
For the attributes in the SPECIAL category, the text in the
specification defining the attribute MUST be consulted for further
handling when multiplexed.
As an example, for the attribute "extmap" [RFC5285], the
specification defining the extension needs to be consulted to
understand the multiplexing implications.
4.9. Category: TBD
The attributes in the TBD category have not been analyzed under the
proposed multiplexing framework and SHOULD NOT be multiplexed.
5. Analysis of Existing Attributes
This section analyzes attributes listed in [IANA], grouped under the
IETF document that defines them.
The "Level" column indicates whether the attribute is currently
specified as:
* S -- Session level
* M -- Media level
* B -- Both (Implies either a session level or a media level
attribute)
* SR -- Source-level (for a single SSRC) [RFC5576]
The "Mux Category" column identifies the multiplexing category
assigned to each attribute, and the "Notes" column captures
additional informative details regarding the assigned category,
wherever necessary.
5.1. RFC 4566: SDP
[RFC4566] defines SDP that is intended for describing multimedia
sessions for the purposes of session announcement, session
invitation, and other forms of multimedia session initiation.
+================+=====================+=======+==================+
| Name | Notes | Level | Mux Category |
+================+=====================+=======+==================+
| sendrecv | Not impacted | B | NORMAL |
+----------------+---------------------+-------+------------------+
| sendonly | Not impacted | B | NORMAL |
+----------------+---------------------+-------+------------------+
| recvonly | Not impacted | B | NORMAL |
+----------------+---------------------+-------+------------------+
| inactive | Not impacted | B | NORMAL |
+----------------+---------------------+-------+------------------+
| cat | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| ptime | The attribute value | M | IDENTICAL-PER-PT |
| | MUST be the same | | |
| | for a given codec | | |
| | configuration. | | |
+----------------+---------------------+-------+------------------+
| maxptime | The attribute value | M | IDENTICAL-PER-PT |
| | MUST be the same | | |
| | for a given codec | | |
| | configuration. | | |
+----------------+---------------------+-------+------------------+
| orient | Not impacted | M | NORMAL |
+----------------+---------------------+-------+------------------+
| framerate | The attribute value | M | IDENTICAL-PER-PT |
| | MUST be the same | | |
| | for a given codec | | |
| | configuration. | | |
+----------------+---------------------+-------+------------------+
| quality | Not impacted | M | NORMAL |
+----------------+---------------------+-------+------------------+
| rtpmap | The attribute value | M | IDENTICAL-PER-PT |
| | MUST be the same | | |
| | for a given codec | | |
| | configuration. | | |
+----------------+---------------------+-------+------------------+
| fmtp | The attribute value | M | IDENTICAL-PER-PT |
| | MUST be the same | | |
| | for a given codec | | |
| | configuration. | | |
+----------------+---------------------+-------+------------------+
| keywds | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| type | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| type:broadcast | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| type:H332 | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| type:meeting | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| type:moderated | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| type:test | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| tool | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| charset | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| sdplang | Not impacted | B | NORMAL |
+----------------+---------------------+-------+------------------+
| lang | Not impacted | B | NORMAL |
+----------------+---------------------+-------+------------------+
Table 1: RFC 4566 Attribute Analysis
5.2. RFC 4585: RTP/AVPF
[RFC4585] defines an extension to the Audio-visual Profile (AVP) that
enables receivers to provide, statistically, more immediate feedback
to the senders and thus allows for short-term adaptation and
efficient feedback-based repair mechanisms to be implemented.
+=========+===========================+=======+==================+
| Name | Notes | Level | Mux Category |
+=========+===========================+=======+==================+
| rtcp-fb | Since RTCP feedback | M | IDENTICAL-PER-PT |
| | attributes are scoped by | | |
| | payload type (PT), their | | |
| | values MUST be identical | | |
| | for a given PT across the | | |
| | multiplexed "m=" lines. | | |
+---------+---------------------------+-------+------------------+
Table 2: RFC 4585 Attribute Analysis
5.3. RFC 5761: Multiplexing RTP and RTCP
[RFC5761] discusses issues that arise when multiplexing RTP data
packets and RTP Control Protocol (RTCP) packets on a single UDP port.
It describes when such multiplexing is and is not appropriate, and it
explains how the SDP can be used to signal multiplexed sessions.
+==========+=================================+=======+==============+
| Name | Notes | Level | Mux |
| | | | Category |
+==========+=================================+=======+==============+
| rtcp-mux | RTP and RTCP multiplexing | M | IDENTICAL |
| | affects the entire RTP session. | | |
+----------+---------------------------------+-------+--------------+
Table 3: RFC 5761 Attribute Analysis
5.4. RFC 3312: Integration of Resource Management and SIP
[RFC3312] defines a generic framework for preconditions, which are
extensible through IANA registration. This document also discusses
how network quality of service can be made a precondition for
establishment of sessions initiated by the Session Initiation
Protocol (SIP). These preconditions require that the participant
reserve network resources before continuing with the session.
+======+======================+=======+==============+
| Name | Notes | Level | Mux Category |
+======+======================+=======+==============+
| des | Refer to notes below | M | CAUTION |
+------+----------------------+-------+--------------+
| conf | Refer to notes below | M | CAUTION |
+------+----------------------+-------+--------------+
| curr | Refer to notes below | M | CAUTION |
+------+----------------------+-------+--------------+
Table 4: RFC 3312 Attribute Analysis
NOTE: A mismatched set of preconditions across media descriptions
results in session establishment failures due to inability to meet
the requested resource reservations.
5.5. RFC 4574: SDP "label" Attribute
[RFC4574] defines a new SDP media-level attribute: "label". The
"label" attribute carries a pointer to a media stream in the context
of an arbitrary network application that uses SDP. The sender of the
SDP document can attach the "label" attribute to a particular media
stream or streams. The application can then use the provided pointer
to refer to each particular media stream in its context.
+=======+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+=======+==============+=======+==============+
| label | Not impacted | M | NORMAL |
+-------+--------------+-------+--------------+
Table 5: RFC 4574 Attribute Analysis
5.6. RFC 5432: QoS Mechanism Selection in SDP
[RFC5432] defines procedures for negotiating QoS mechanisms using the
SDP offer/answer model.
+===============+======================+=======+==============+
| Name | Notes | Level | Mux Category |
+===============+======================+=======+==============+
| qos-mech-send | Refer to Section 10. | B | TRANSPORT |
+---------------+----------------------+-------+--------------+
| qos-mech-recv | Refer to Section 10. | B | TRANSPORT |
+---------------+----------------------+-------+--------------+
Table 6: RFC 5432 Attribute Analysis
5.7. RFC 4568: SDP Security Descriptions
[RFC4568] defines an SDP cryptographic attribute for unicast media
streams. The attribute describes a cryptographic key and other
parameters that serve to configure security for a unicast media
stream in either a single message or a roundtrip exchange.
+========+=================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+========+=================================+=======+===========+
| crypto | crypto attribute MUST be the | M | TRANSPORT |
| | one that corresponds to the | | |
| | "m=" line chosen for setting up | | |
| | the underlying transport flow. | | |
+--------+---------------------------------+-------+-----------+
Table 7: RFC 4568 Attribute Analysis
5.8. RFC 5762: RTP over DCCP
RTP is a widely used transport for real-time multimedia on IP
networks. DCCP is a transport protocol that provides desirable
services for real-time applications. [RFC5762] specifies a mapping
of RTP onto DCCP, along with associated signaling, such that real-
time applications can make use of the services provided by DCCP.
+===================+======================+=========+==========+
| Name | Notes | Current | Mux |
| | | | Category |
+===================+======================+=========+==========+
| dccp-service-code | If RFC 6773 is not | M | CAUTION |
| | being used in | | |
| | addition to RFC5762, | | |
| | the port in the "m=" | | |
| | line is a DCCP port. | | |
| | Being a connection- | | |
| | oriented protocol, | | |
| | DCCP does not allow | | |
| | multiple connections | | |
| | on the same 5-tuple. | | |
+-------------------+----------------------+---------+----------+
Table 8: RFC 5762 Attribute Analysis
NOTE: If RFC 6773 is being used in addition to RFC 5762, and the
DCCP-in-UDP layer has additional demultiplexing, then it may be
possible to use different DCCP service codes for each DCCP flow,
given each uses a different DCCP port. However, doing so might
conflict with the media type of the "m=" line. None of this is
standardized yet, and it wouldn't work as explained. Hence
performing multiplexing is not recommended even in this alternate
scenario.
5.9. RFC 6773: DCCP-UDP Encapsulation
[RFC6773] specifies an alternative encapsulation of DCCP, referred to
as DCCP-UDP. This encapsulation allows DCCP to be carried through
the current generation of Network Address Translation (NAT)
middleboxes without modification of those middleboxes.
+===========+==============================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+===========+==============================+=======+==========+
| dccp-port | Multiplexing is not | M | CAUTION |
| | recommended due to potential | | |
| | conflict between the port | | |
| | used for DCCP encapsulation/ | | |
| | decapsulation and the RTP. | | |
+-----------+------------------------------+-------+----------+
Table 9: RFC 6773 Attribute Analysis
NOTE: RFC 6773 allows DCCP-UDP encapsulation, with the UDP port being
the port of the DCCP encapsulation/decapsulation service. This
encapsulation allows arbitrary DCCP packets to be encapsulated, and
the DCCP port chosen can conflict with the port chosen for the RTP
traffic. Multiplexing several DCCP-in-UDP encapsulations on the same
UDP port with no RTP traffic on the same port implies collapsing
several DCCP port spaces together. Whether or not this works depends
on the nature of DCCP encapsulation and ports choices; it is thus
very application dependent.
5.10. RFC 5506: Reduced-Size RTCP in RTP Profile
[RFC5506] discusses benefits and issues that arise when allowing RTCP
packets to be transmitted with reduced size.
+============+===========================+=======+==============+
| Name | Notes | Level | Mux Category |
+============+===========================+=======+==============+
| rtcp-rsize | Reduced-size RTCP affects | M | IDENTICAL |
| | the entire RTP session. | | |
+------------+---------------------------+-------+--------------+
Table 10: RFC 5506 Attribute Analysis
5.11. RFC 6787: Media Resource Control Protocol Version 2
The Media Resource Control Protocol Version 2 (MRCPv2) allows client
hosts to control media service resources such as speech synthesizers,
recognizers, verifiers, and identifiers residing in servers on the
network. MRCPv2 is not a "stand-alone" protocol; it relies on other
protocols, such as the SIP, to coordinate MRCPv2 clients and servers
and manage session between them, and SDP to describe, discover, and
exchange capabilities. It also depends on SIP and SDP to establish
the media sessions and associated parameters between the media source
or sink and the media server. Once this is done, the MRCPv2 exchange
operates over the control session established above, allowing the
client to control the media-processing resources on the speech
resource server. [RFC6787] defines attributes for this purpose.
+==========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+==========+==============+=======+==============+
| resource | Not impacted | M | NORMAL |
+----------+--------------+-------+--------------+
| channel | Not impacted | M | NORMAL |
+----------+--------------+-------+--------------+
| cmid | Not impacted | M | NORMAL |
+----------+--------------+-------+--------------+
Table 11: RFC 6787 Attribute Analysis
5.12. RFC 8445: ICE
[RFC8445] describes a protocol for NAT traversal for UDP-based
multimedia sessions established with the offer/answer model. ICE
makes use of the Session Traversal Utilities for NAT (STUN) protocol
and its extension, Traversal Using Relay NAT (TURN). ICE can be used
by any protocol utilizing the offer/answer model, such as the SIP.
+===================+===========================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+===================+===========================+=======+===========+
| ice-lite | Not impacted | S | NORMAL |
+-------------------+---------------------------+-------+-----------+
| ice-options | Not impacted | S | NORMAL |
+-------------------+---------------------------+-------+-----------+
| ice-mismatch | Not impacted | S | NORMAL |
+-------------------+---------------------------+-------+-----------+
| ice-pwd | ice-pwd MUST be the one | B | TRANSPORT |
| | that corresponds to the | | |
| | "m=" line chosen for | | |
| | setting up the | | |
| | underlying transport | | |
| | flow. | | |
+-------------------+---------------------------+-------+-----------+
| ice-ufrag | ice-ufrag MUST be the | B | TRANSPORT |
| | one that corresponds to | | |
| | the "m=" line chosen | | |
| | for setting up the | | |
| | underlying transport | | |
| | flow. | | |
+-------------------+---------------------------+-------+-----------+
| candidate | ice candidate MUST be | M | TRANSPORT |
| | the one that | | |
| | corresponds to the "m=" | | |
| | line chosen for setting | | |
| | up the underlying | | |
| | transport flow. | | |
+-------------------+---------------------------+-------+-----------+
| remote-candidates | ice remote candidate | M | TRANSPORT |
| | MUST be the one that | | |
| | corresponds to the "m=" | | |
| | line chosen for setting | | |
| | up the underlying | | |
| | transport flow. | | |
+-------------------+---------------------------+-------+-----------+
| ice2 | Not impacted | S | NORMAL |
+-------------------+---------------------------+-------+-----------+
Table 12: RFC 8445 Attribute Analysis
5.13. RFC 5285: RTP Header Extensions
[RFC5285] provides a general mechanism for using the header-extension
feature of RTP. (Note: [RFC5285] has been obsoleted by [RFC8285].)
It provides the option to use a small number of small extensions in
each RTP packet, where the universe of possible extensions is large
and registration is decentralized. The actual extensions in use in a
session are signaled in the setup information for that session.
+========+================================+=======+==============+
| Name | Notes | Level | Mux Category |
+========+================================+=======+==============+
| extmap | Refer to the document defining | B | SPECIAL |
| | the specific RTP extension. | | |
+--------+--------------------------------+-------+--------------+
Table 13: RFC 5285 Attribute Analysis
5.14. RFC 3605: RTCP Attribute in SDP
Originally, SDP assumed that RTP and RTCP were carried on consecutive
ports. However, this is not always true when NATs are involved.
[RFC3605] specifies an early mechanism for indicating the RTCP port.
+======+================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+======+================================+=======+===========+
| rtcp | RTCP port MUST be the one that | M | TRANSPORT |
| | corresponds to the "m=" line | | |
| | chosen for setting up the | | |
| | underlying transport flow. | | |
+------+--------------------------------+-------+-----------+
Table 14: RFC 3605 Attribute Analysis
5.15. RFC 5576: Source-Specific SDP Attributes
[RFC5576] defines a mechanism for describing RTP media sources --
which are identified by their synchronization source (SSRC)
identifiers -- in SDP, to associate attributes with these sources and
express relationships among sources. It also defines several source-
level attributes that can be used to describe properties of media
sources.
+===============+=====================+=======+==================+
| Name | Notes | Level | Mux Category |
+===============+=====================+=======+==================+
| ssrc | Refer to notes | M | NORMAL |
| | below. | | |
+---------------+---------------------+-------+------------------+
| ssrc-group | Refer to Section 9 | M | NORMAL |
| | for specific | | |
| | analysis of the | | |
| | grouping semantics. | | |
+---------------+---------------------+-------+------------------+
| cname | Not impacted | SR | NORMAL |
+---------------+---------------------+-------+------------------+
| previous-ssrc | Refer to notes | SR | NORMAL |
| | below | | |
+---------------+---------------------+-------+------------------+
| fmtp | The attribute value | SR | IDENTICAL-PER-PT |
| | MUST be the same | | |
| | for a given codec | | |
| | configuration. | | |
+---------------+---------------------+-------+------------------+
Table 15: RFC 5576 Attribute Analysis
NOTE: If SSRCs are repeated across "m=" lines being multiplexed, they
MUST all represent the same underlying RTP Source.
5.16. RFC 7273: RTP Clock Source Signaling
[RFC7273] specifies SDP signaling that identifies timestamp reference
clock sources and SDP signaling that identifies the media clock
sources in a multimedia session.
+===================+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===================+==============+=======+==============+
| ts-refclk | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| mediaclk | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:ntp | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:ptp | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:gps | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:gal | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:glonass | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:local | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:private | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| mediaclk:sender | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| mediaclk:direct | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| mediaclk:IEEE1722 | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
Table 16: RFC 7273 Attribute Analysis
5.17. RFC 6236: Image Attributes in SDP
[RFC6236] proposes a new generic session setup attribute to make it
possible to negotiate different image attributes, such as image size.
A possible use case is to make it possible for a low-end handheld
terminal to display video without the need to rescale the image,
something that may consume large amounts of memory and processing
power. The document also helps to maintain an optimal bitrate for
video as only the image size that is desired by the receiver is
transmitted.
+===========+==========================+=======+==================+
| Name | Notes | Level | Mux Category |
+===========+==========================+=======+==================+
| imageattr | The attribute value MUST | M | IDENTICAL-PER-PT |
| | be the same for a given | | |
| | codec configuration. | | |
+-----------+--------------------------+-------+------------------+
Table 17: RFC 6236 Attribute Analysis
5.18. RFC 7197: Duplication Delay Attribute in SDP
[RFC7197] defines an attribute to indicate the presence of temporally
redundant media streams and the duplication delay in SDP.
+===================+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===================+==============+=======+==============+
| duplication-delay | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
Table 18: RFC 7197 Attribute Analysis
5.19. RFC 7266: RTCP XR Blocks for MOS Metric Reporting
[RFC7266] defines an RTCP Extended Report (XR) Block that includes
two new segment types and associated SDP parameters that allow the
reporting of mean opinion score (MOS) metrics for use in a range of
RTP applications.
+============+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+============+==============+=======+==============+
| calgextmap | Not impacted | B | NORMAL |
+------------+--------------+-------+--------------+
Table 19: RFC 7266 Attribute Analysis
5.20. RFC 6285: Rapid Acquisition of Multicast RTP Sessions
[RFC6285] describes a method of using the existing RTP and RTCP
machinery that reduces the acquisition delay. In this method, an
auxiliary unicast RTP session carrying the reference information to
the receiver precedes or accompanies the multicast stream. This
unicast RTP flow can be transmitted at a faster-than-natural bitrate
to further accelerate the acquisition. The motivating use case for
this capability is multicast applications that carry real-time
compressed audio and video.
+==============+=================+=======+==============+
| Name | Notes | Level | Mux Category |
+==============+=================+=======+==============+
| rams-updates | Not recommended | M | CAUTION |
+--------------+-----------------+-------+--------------+
Table 20: RFC 6285 Attribute Analysis
5.21. RFC 6230: Media Control Channel Framework
[RFC6230] describes a framework and protocol for application
deployment where the application programming logic and media
processing are distributed. This implies that application
programming logic can seamlessly gain access to appropriate resources
that are not co-located on the same physical network entity. The
framework uses SIP to establish an application-level control
mechanism between application servers and associated external servers
such as media servers.
+========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+========+==============+=======+==============+
| cfw-id | Not impacted | M | NORMAL |
+--------+--------------+-------+--------------+
Table 21: RFC 6230 Attribute Analysis
5.22. RFC 6364: SDP Elements for FEC Framework
[RFC6364] specifies the use of SDP to describe the parameters
required to signal the Forward Error Correction (FEC) Framework
Configuration Information between the sender(s) and receiver(s).
This document also provides examples that show the semantics for
grouping multiple source and repair flows together for the
applications that simultaneously use multiple instances of the FEC
Framework.
+=================+======================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+=================+======================+=======+==========+
| fec-source-flow | Refer to the | M | SPECIAL |
| | document defining | | |
| | specific FEC scheme. | | |
+-----------------+----------------------+-------+----------+
| fec-repair-flow | Refer to the | M | SPECIAL |
| | document defining | | |
| | specific FEC scheme. | | |
+-----------------+----------------------+-------+----------+
| repair-window | Refer to the | M | SPECIAL |
| | document defining | | |
| | specific FEC scheme. | | |
+-----------------+----------------------+-------+----------+
Table 22: RFC 6364 Attribute Analysis
5.23. RFC 4796: "content" Attribute
[RFC4796] defines a new SDP media-level attribute, "content". The
"content" attribute defines the content of the media stream to a more
detailed level than the media description line. The sender of an SDP
session description can attach the "content" attribute to one or more
media streams. The receiving application can then treat each media
stream differently (e.g., show it on a big or small screen) based on
its content.
+=========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+==============+=======+==============+
| content | Not impacted | M | NORMAL |
+---------+--------------+-------+--------------+
Table 23: RFC 4796 Attribute Analysis
5.24. RFC 3407: SDP Simple Capability Declaration
[RFC3407] defines a set of SDP attributes that enables SDP to provide
a minimal and backwards-compatible capability declaration mechanism.
+=========+======================+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+======================+=======+==============+
| sqn | Not impacted | B | NORMAL |
+---------+----------------------+-------+--------------+
| cdsc | Not impacted | B | NORMAL |
+---------+----------------------+-------+--------------+
| cpar | Refer to Section 14 | B | INHERIT |
+---------+----------------------+-------+--------------+
| cparmin | Refer to notes below | B | SPECIAL |
+---------+----------------------+-------+--------------+
| cparmax | Refer to notes below | B | SPECIAL |
+---------+----------------------+-------+--------------+
Table 24: RFC 3407 Attribute Analysis
NOTE: The attributes "a=cparmin" and "a=cparmax" define minimum and
maximum numerical values associated with the attributes described in
"a=cpar".
Since the cpar attribute can either define a "b=" attribute or any
"a=" attribute, the multiplexing category depends on the actual
attribute being encapsulated and the implications of the numerical
values assigned. Hence it is recommended to consult the
specification defining attributes "cparmin" and "cparmax" to further
analyze their behavior under multiplexing.
5.25. RFC 6284: Port Mapping between Unicast and Multicast RTP Sessions
[RFC6284] presents a port-mapping solution that allows RTP receivers
to choose their own ports for an auxiliary unicast session in RTP
applications using both unicast and multicast services. The solution
provides protection against denial-of-service or packet amplification
attacks that could be used to cause one or more RTP packets to be
sent to a victim client.
+=================+=========================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+=================+=========================+=======+==========+
| portmapping-req | Not recommended if port | M | CAUTION |
| | mapping is required by | | |
| | the application | | |
+-----------------+-------------------------+-------+----------+
Table 25: RFC 6284 Attribute Analysis
5.26. RFC 6714: MSRP-CEMA
[RFC6714] defines a Message Session Relay Protocol (MSRP) extension,
Connection Establishment for Media Anchoring (CEMA). Support of this
extension is optional. The extension allows middleboxes to anchor
the MSRP connection without the need for middleboxes to modify the
MSRP messages; thus, it also enables secure end-to-end MSRP
communication in networks where such middleboxes are deployed. This
document also defines an SDP attribute, "msrp-cema", that MSRP
endpoints use to indicate support of the CEMA extension.
+===========+======================+=======+==============+
| Name | Notes | Level | Mux Category |
+===========+======================+=======+==============+
| msrp-cema | Refer to notes below | M | TBD |
+-----------+----------------------+-------+--------------+
Table 26: RFC 6714 Attribute Analysis
NOTE: As per Section 9 of [RFC8843], there exists no publicly
available specification that defines procedures for multiplexing/
demultiplexing MSRP flows over a single 5-tuple. Once such a
specification is available, the assignments of multiplexing
categories for the attributes in this section could be revisited.
5.27. RFC 4583: SDP Format for BFCP Streams
[RFC4583] specifies how to describe Binary Floor Control Protocol
(BFCP) streams in SDP descriptions. User agents using the offer/
answer model to establish BFCP streams use this format in their
offers and answers.
+===========+======================+=======+==============+
| Name | Notes | Level | Mux Category |
+===========+======================+=======+==============+
| floorctrl | Refer to notes below | M | TBD |
+-----------+----------------------+-------+--------------+
| confid | Refer to notes below | M | TBD |
+-----------+----------------------+-------+--------------+
| userid | Refer to notes below | M | TBD |
+-----------+----------------------+-------+--------------+
| floorid | Refer to notes below | M | TBD |
+-----------+----------------------+-------+--------------+
Table 27: RFC 4583 Attribute Analysis
NOTE: [RFC4583] has been obsoleted by [RFC8856], which redefines the
SDP attributes listed in this section, including the "Mux Category"
values. However, [RFC8856] does not change the "Mux Category" values
of the attributes.
NOTE: As per Section 9 of [RFC8843], there exists no publicly
available specification that defines procedures for multiplexing/
demultiplexing BFCP streams over a single 5-tuple. Once such a
specification is available, the assignments of multiplexing
categories for the attributes in this section could be revisited.
5.28. RFC 5547: SDP Offer/Answer for File Transfer
[RFC5547] provides a mechanism to negotiate the transfer of one or
more files between two endpoints by using the SDP offer/answer model
specified in [RFC3264].
+==================+======================+=======+==============+
| Name | Notes | Level | Mux Category |
+==================+======================+=======+==============+
| file-selector | Refer to notes below | M | TBD |
+------------------+----------------------+-------+--------------+
| file-transfer-id | Refer to notes below | M | TBD |
+------------------+----------------------+-------+--------------+
| file-disposition | Refer to notes below | M | TBD |
+------------------+----------------------+-------+--------------+
| file-date | Refer to notes below | M | TBD |
+------------------+----------------------+-------+--------------+
| file-icon | Refer to notes below | M | TBD |
+------------------+----------------------+-------+--------------+
| file-range | Refer to notes below | M | TBD |
+------------------+----------------------+-------+--------------+
Table 28: RFC 5547 Attribute Analysis
NOTE: As per Section 9 of [RFC8843], there exists no publicly
available specification that defines procedures for multiplexing/
demultiplexing MSRP flows over a single 5-tuple. Once such a
specification is available, the assignments of multiplexing
categories for attributes in this section could be revisited.
5.29. RFC 6849: SDP and RTP Media Loopback Extension
[RFC6849] adds new SDP media types and attributes that enable
establishment of media sessions where the media is looped back to the
transmitter. Such media sessions will serve as monitoring and
troubleshooting tools by providing the means for measurement of more
advanced Voice over IP (VoIP), real-time text, and Video over IP
performance metrics.
+====================+================+=======+==================+
| Name | Notes | Level | Mux Category |
+====================+================+=======+==================+
| loopback rtp-pkt- | The attribute | M | IDENTICAL-PER-PT |
| loopback | value MUST be | | |
| | same for a | | |
| | given codec | | |
| | configuration. | | |
+--------------------+----------------+-------+------------------+
| loopback rtp- | The attribute | M | IDENTICAL-PER-PT |
| media-loopback | value MUST be | | |
| | same for a | | |
| | given codec | | |
| | configuration. | | |
+--------------------+----------------+-------+------------------+
| loopback-source | Not impacted | M | NORMAL |
+--------------------+----------------+-------+------------------+
| loopback-mirror | Not impacted | M | NORMAL |
+--------------------+----------------+-------+------------------+
Table 29: RFC 6849 Analysis
5.30. RFC 5760: RTCP with Unicast Feedback
[RFC5760] specifies an extension to RTCP to use unicast feedback to a
multicast sender. The proposed extension is useful for single-source
multicast sessions such as source-specific multicast (SSM)
communication where the traditional model of many-to-many group
communication is either not available or not desired.
+==============+=========================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+==============+=========================+=======+===========+
| rtcp-unicast | The attribute MUST be | M | IDENTICAL |
| | reported across all | | |
| | multiplexed "m=" lines. | | |
+--------------+-------------------------+-------+-----------+
Table 30: RFC 5760 Attribute Analysis
5.31. RFC 3611: RTCP XR
[RFC3611] defines the Extended Report (XR) packet type for RTCP and
defines how the use of XR packets can be signaled by an application
if it employs the Session Description Protocol (SDP).
+=========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+==============+=======+==============+
| rtcp-xr | Not impacted | B | NORMAL |
+---------+--------------+-------+--------------+
Table 31: RFC 3611 Attribute Analysis
5.32. RFC 5939: SDP Capability Negotiation
[RFC5939] defines a general SDP Capability Negotiation framework. It
also specifies how to provide attributes and transport protocols as
capabilities and negotiate them using the framework. Extensions for
other types of capabilities (e.g., media types and media formats) may
be provided in other documents.
+========+=====================+=======+==============+
| Name | Notes | Level | Mux Category |
+========+=====================+=======+==============+
| pcfg | Refer to Section 14 | M | SPECIAL |
+--------+---------------------+-------+--------------+
| acfg | Refer to Section 14 | M | SPECIAL |
+--------+---------------------+-------+--------------+
| csup | Not impacted | B | NORMAL |
+--------+---------------------+-------+--------------+
| creq | Not impacted | B | NORMAL |
+--------+---------------------+-------+--------------+
| acap | Refer to Section 14 | B | INHERIT |
+--------+---------------------+-------+--------------+
| tcap | Refer to Section 14 | B | INHERIT |
+--------+---------------------+-------+--------------+
| cap-v0 | Not impacted | B | NORMAL |
+--------+---------------------+-------+--------------+
Table 32: RFC 5939 Attribute Analysis
5.33. RFC 6871: SDP Media Capabilities Negotiation
SDP capability negotiation provides a general framework for
indicating and negotiating capabilities in SDP. The base framework
only defines capabilities for negotiating transport protocols and
attributes. [RFC6871] extends the framework by defining media
capabilities that can be used to negotiate media types and their
associated parameters.
+========+======================+=======+==================+
| Name | Notes | Level | Mux Category |
+========+======================+=======+==================+
| rmcap | Refer to Section 14 | B | IDENTICAL-PER-PT |
+--------+----------------------+-------+------------------+
| omcap | Not impacted | B | NORMAL |
+--------+----------------------+-------+------------------+
| mfcap | Refer to Section 14 | B | IDENTICAL-PER-PT |
+--------+----------------------+-------+------------------+
| mscap | Refer to Section 14 | B | INHERIT |
+--------+----------------------+-------+------------------+
| lcfg | Refer to Section 14 | B | SPECIAL |
+--------+----------------------+-------+------------------+
| sescap | Refer to notes below | S | CAUTION |
+--------+----------------------+-------+------------------+
| med-v0 | Not impacted | S | NORMAL |
+--------+----------------------+-------+------------------+
Table 33: RFC 6871 Attribute Analysis
NOTE: The "sescap" attribute is not recommended for use with
multiplexing. The reason is that it requires the use of unique
configuration numbers across the entire SDP (per [RFC6871]) as
opposed to within a media description only (per [RFC5939]). As
described in Section 14, the use of identical configuration numbers
between multiplexed (bundled) media descriptions is the default way
of indicating compatible configurations in a bundle.
5.34. RFC 7006: Miscellaneous Capabilities Negotiation in SDP
[RFC7006] extends the SDP Capability Negotiation framework to allow
endpoints to negotiate three additional SDP capabilities. In
particular, this memo provides a mechanism to negotiate bandwidth
("b=" line), connection data ("c=" line), and session or media titles
("i=" line for each session or media).
+=========+==================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+=========+==================================+=======+===========+
| bcap | Inherit the category SUM as | B | INHERIT |
| | applicable to the "b=" attribute | | |
+---------+----------------------------------+-------+-----------+
| bcap-v0 | Not impacted | B | NORMAL |
+---------+----------------------------------+-------+-----------+
| ccap | The connection address type MUST | B | IDENTICAL |
| | be identical across all the | | |
| | multiplexed "m=" lines. | | |
+---------+----------------------------------+-------+-----------+
| ccap-v0 | Not impacted | B | NORMAL |
+---------+----------------------------------+-------+-----------+
| icap | Not impacted | B | NORMAL |
+---------+----------------------------------+-------+-----------+
| icap-v0 | Not impacted | B | NORMAL |
+---------+----------------------------------+-------+-----------+
Table 34: RFC 7006 Attribute Analysis
5.35. RFC 4567: Key Management Extensions for SDP and RTSP
[RFC4567] defines general extensions for SDP and Real-Time Streaming
Protocol (RTSP) to carry messages, as specified by a key management
protocol, in order to secure the media. These extensions are
presented as a framework to be used by one or more key management
protocols. As such, their use is meaningful only when complemented
by an appropriate key management protocol.
+==========+==========================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+==========+==========================+=======+===========+
| key-mgmt | Key management protocol | B | IDENTICAL |
| | MUST be identical across | | |
| | all the "m=" lines. | | |
+----------+--------------------------+-------+-----------+
| mikey | Key management protocol | B | IDENTICAL |
| | MUST be identical across | | |
| | all the "m=" lines. | | |
+----------+--------------------------+-------+-----------+
Table 35: RFC 4567 Attribute Analysis
5.36. RFC 4572: Comedia over TLS in SDP
[RFC4572] specifies how to establish secure connection-oriented media
transport sessions over the Transport Layer Security (TLS) protocol
using SDP. (Note: [RFC4572] has been obsoleted by [RFC8122].) It
defines a new SDP protocol identifier, "TCP/TLS". It also defines
the syntax and semantics for an SDP "fingerprint" attribute that
identifies the certificate that will be presented for the TLS
session. This mechanism allows media transport over TLS connections
to be established securely, so long as the integrity of session
descriptions is assured.
+=============+=================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+=============+=================================+=======+===========+
| fingerprint | fingerprint value MUST be | B | TRANSPORT |
| | the one that corresponds | | |
| | to the "m=" line chosen | | |
| | for setting up the | | |
| | underlying transport flow. | | |
+-------------+---------------------------------+-------+-----------+
Table 36: RFC 4572 Attribute Analysis
5.37. RFC 4570: SDP Source Filters
[RFC4570] describes how to adapt SDP to express one or more source
addresses as a source filter for one or more destination "connection"
addresses. It defines the syntax and semantics for an SDP "source-
filter" attribute that may reference either IPv4 or IPv6 address(es)
as either an inclusive or exclusive source list for either multicast
or unicast destinations. In particular, an inclusive source filter
can be used to specify a source-specific multicast (SSM) session.
+===============+=========================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+===============+=========================+=======+===========+
| source-filter | The attribute MUST be | B | IDENTICAL |
| | repeated across all | | |
| | multiplexed "m=" lines. | | |
+---------------+-------------------------+-------+-----------+
Table 37: RFC 4570 Attribute Analysis
5.38. RFC 6128: RTCP Port for Multicast Sessions
SDP has an attribute that allows RTP applications to specify an
address and a port associated with the RTCP traffic. In RTP-based
source-specific multicast (SSM) sessions, the same attribute is used
to designate the address and the RTCP port of the Feedback Target in
the SDP description. However, the RTCP port associated with the SSM
session itself cannot be specified by the same attribute to avoid
ambiguity and thus is required to be derived from the "m=" line of
the media description. Deriving the RTCP port from the "m=" line
imposes an unnecessary restriction. [RFC6128] removes this
restriction by introducing a new SDP attribute.
+================+==========================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+================+==========================+=======+===========+
| multicast-rtcp | Multicast RTCP port MUST | B | IDENTICAL |
| | be identical across all | | |
| | the "m=" lines. | | |
+----------------+--------------------------+-------+-----------+
Table 38: RFC 6128 Attribute Analysis
5.39. RFC 6189: ZRTP
[RFC6189] defines ZRTP, a protocol for media path Diffie-Hellman
exchange to agree on a session key and parameters for establishing
unicast SRTP sessions for VoIP applications.
+===========+=================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+===========+=================================+=======+===========+
| zrtp-hash | The zrtp-hash attribute MUST be | M | TRANSPORT |
| | the one that corresponds to the | | |
| | "m=" line chosen for setting up | | |
| | the underlying transport flow. | | |
+-----------+---------------------------------+-------+-----------+
Table 39: RFC 6189 Attribute Analysis
5.40. RFC 4145: Connection-Oriented Media
[RFC4145] describes how to express media transport over TCP using
SDP. It defines the SDP "TCP" protocol identifier, the SDP "setup"
attribute, which describes the connection setup procedure, and the
SDP "connection" attribute, which handles connection re-
establishment.
+============+==================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+============+==================================+=======+===========+
| setup | The setup attribute MUST be the | B | TRANSPORT |
| | one that corresponds to the | | |
| | "m=" line chosen for setting up | | |
| | the underlying transport flow. | | |
+------------+----------------------------------+-------+-----------+
| connection | The connection attribute MUST | B | TRANSPORT |
| | be the one that corresponds to | | |
| | the "m=" line chosen for | | |
| | setting up the underlying | | |
| | transport flow. | | |
+------------+----------------------------------+-------+-----------+
Table 40: RFC 4145 Attribute Analysis
5.41. RFC 6947: The SDP "altc" Attribute
[RFC6947] proposes a mechanism that allows the same SDP offer to
carry multiple IP addresses of different address families (e.g., IPv4
and IPv6). The proposed "altc" attribute solves the backward-
compatibility problem that plagued Alternative Network Address Types
(ANAT) due to their syntax.
+======+=================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+======+=================================+=======+===========+
| altc | The IP address and port MUST be | M | TRANSPORT |
| | the ones that correspond to the | | |
| | "m=" line chosen for setting up | | |
| | the underlying transport flow. | | |
+------+---------------------------------+-------+-----------+
Table 41: RFC 6947 Attribute Analysis
5.42. RFC 7195: SDP Extension for Circuit-Switched Bearers in PSTN
[RFC7195] describes use cases, requirements, and protocol extensions
for using the SDP offer/answer model for establishing audio and video
media streams over circuit-switched bearers in the Public Switched
Telephone Network (PSTN).
+=========================+=============+=======+==============+
| Name | Notes | Level | Mux Category |
+=========================+=============+=======+==============+
| cs-correlation:callerid | Refer to | M | TBD |
| | notes below | | |
+-------------------------+-------------+-------+--------------+
| cs-correlation:uuie | Refer to | M | TBD |
| | notes below | | |
+-------------------------+-------------+-------+--------------+
| cs-correlation:dtmf | Refer to | M | TBD |
| | notes below | | |
+-------------------------+-------------+-------+--------------+
| cs-correlation:external | Refer to | M | TBD |
| | notes below | | |
+-------------------------+-------------+-------+--------------+
Table 42: RFC 7195 Attribute Analysis
NOTE: [RFC7195] defines SDP attributes for establishing audio and
video media streams over circuit-switched bearers by defining a new
nettype value, "PSTN". However, Section 7.2 of [RFC8843] requires
the "c=" line nettype value to be "IN". If there exists in future a
specification that defines procedures to multiplex media streams over
nettype "PSTN", the multiplexing categories for attributes in this
section could be revisited.
5.43. RFC 7272: IDMS Using the RTP Control Protocol (RTCP)
[RFC7272] defines a new RTCP packet type and an RTCP Extended Report
(XR) Block Type to be used for achieving Inter-Destination Media
Synchronization (IDMS).
+===========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===========+==============+=======+==============+
| rtcp-idms | Not impacted | M | NORMAL |
+-----------+--------------+-------+--------------+
Table 43: RFC 7272 Attribute Analysis
5.44. RFC 5159: Open Mobile Alliance (OMA) Broadcast (BCAST) SDP
Attributes
[RFC5159] provides descriptions of SDP attributes used by the Open
Mobile Alliance's "Service and Content Protection for Mobile
Broadcast Services" specification.
+====================+===============+=======+==============+
| Name | Notes | Level | Mux Category |
+====================+===============+=======+==============+
| bcastversion | Not impacted | S | NORMAL |
+--------------------+---------------+-------+--------------+
| stkmstream | Not impacted | B | NORMAL |
+--------------------+---------------+-------+--------------+
| SRTPAuthentication | Needs further | M | TBD |
| | analysis | | |
+--------------------+---------------+-------+--------------+
| SRTPROCTxRate | Needs further | M | TBD |
| | analysis | | |
+--------------------+---------------+-------+--------------+
Table 44: RFC 5159 Attribute Analysis
5.45. RFC 6193: Media Description for IKE in SDP
[RFC6193] specifies how to establish a media session that represents
a virtual private network using the Session Initiation Protocol for
the purpose of on-demand media/application sharing between peers. It
extends the protocol identifier of SDP so that it can negotiate use
of the Internet Key Exchange Protocol (IKE) for media sessions in the
SDP offer/answer model.
+==================+============================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+==================+============================+=======+==========+
| ike-setup | Unlikely to use IKE in the | B | CAUTION |
| | context of multiplexing | | |
+------------------+----------------------------+-------+----------+
| psk-fingerprint | Unlikely to use IKE in the | B | CAUTION |
| | context of multiplexing | | |
+------------------+----------------------------+-------+----------+
| ike-esp | Unlikely to use IKE in the | B | CAUTION |
| | context of multiplexing | | |
+------------------+----------------------------+-------+----------+
| ike-esp-udpencap | Unlikely to use IKE in the | B | CAUTION |
| | context of multiplexing | | |
+------------------+----------------------------+-------+----------+
Table 45: RFC 6193 Attribute Analysis
5.46. RFC 2326: Real Time Streaming Protocol
The Real Time Streaming Protocol, or RTSP, is an application-level
protocol for control over the delivery of data with real-time
properties. RTSP provides an extensible framework to enable
controlled, on-demand delivery of real-time data, such as audio and
video.
+=========+=======================+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+=======================+=======+==============+
| etag | RFC 2326 is obsolete. | B | CAUTION |
+---------+-----------------------+-------+--------------+
| range | RFC 2326 is obsolete. | B | CAUTION |
+---------+-----------------------+-------+--------------+
| control | RFC 2326 is obsolete. | B | CAUTION |
+---------+-----------------------+-------+--------------+
| mtag | RFC 2326 is obsolete. | B | CAUTION |
+---------+-----------------------+-------+--------------+
Table 46: RFC 2326 Attribute Analysis
NOTE: [RFC2326] defines SDP attributes that are applicable in the
declarative usage of SDP alone. For the purposes of this document,
only the offer/answer usage of SDP is considered to be mandated by
[RFC8843].
5.47. RFC 7826: Real-Time Streaming Protocol
The Real-Time Streaming Protocol, or RTSP, is an application-level
protocol for control over the delivery of data with real-time
properties. RTSP provides an extensible framework to enable
controlled, on-demand delivery of real-time data, such as audio and
video.
+=========+===========================+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+===========================+=======+==============+
| range | RTSP is not supported for | B | CAUTION |
| | RTP stream multiplexing. | | |
+---------+---------------------------+-------+--------------+
| control | RTSP is not supported for | B | CAUTION |
| | RTP stream multiplexing. | | |
+---------+---------------------------+-------+--------------+
| mtag | RTSP is not supported for | B | CAUTION |
| | RTP stream multiplexing. | | |
+---------+---------------------------+-------+--------------+
Table 47: RFC 7826 Attribute Analysis
NOTE: [RFC7826] defines SDP attributes that are applicable in the
declarative usage of SDP alone. For the purposes of this document,
only the offer/answer usage of SDP is considered to be mandated by
[RFC8843].
5.48. RFC 6064: SDP and RTSP Extensions for 3GPP
The Packet-switched Streaming Service (PSS) and the Multimedia
Broadcast/Multicast Service (MBMS) defined by 3GPP use SDP and RTSP
with some extensions. [RFC6064] provides information about these
extensions and registers the RTSP and SDP extensions with IANA.
+==============================+=============+=======+==============+
| Name | Notes | Level | Mux |
| | | | Category |
+==============================+=============+=======+==============+
| X-predecbufsize | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| X-initpredecbufperiod | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| X-initpostdecbufperiod | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| X-decbyterate | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3gpp-videopostdecbufsize | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| framesize | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-Integrity-Key | Refer to | S | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-SDP-Auth | Refer to | S | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-SRTP-Config | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| alt | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| alt-default-id | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| alt-group | Refer to | S | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-Adaptation-Support | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-Asset-Information | Refer to | B | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| mbms-mode | Refer to | B | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| mbms-flowid | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| mbms-repair | Refer to | B | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Corruption | Refer to | M | CAUTION |
| duration | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Rebuffering | Refer to | M | CAUTION |
| duration | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Initial | Refer to | M | CAUTION |
| buffering duration | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Successive | Refer to | M | CAUTION |
| loss of RTP packets | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Frame rate | Refer to | M | CAUTION |
| deviation | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Jitter | Refer to | M | CAUTION |
| duration | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Content | Refer to | B | CAUTION |
| Switch Time | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Average | Refer to | M | CAUTION |
| Codec Bitrate | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Codec | Refer to | M | CAUTION |
| Information | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Buffer | Refer to | M | CAUTION |
| Status | notes below | | |
+------------------------------+-------------+-------+--------------+
Table 48: RFC 6064 Attribute Analysis
NOTE: [RFC6064] defines SDP attributes that are applicable in the
declarative usage of SDP alone. For the purposes of this document,
only the offer/answer usage of SDP is considered to be mandated by
[RFC8843].
5.49. RFC 3108: ATM SDP
[RFC3108] describes conventions for using SDP described for
controlling ATM bearer connections and any associated ATM Adaptation
Layer (AAL).
+=======================+=============+=======+==============+
| Name | Notes | Level | Mux Category |
+=======================+=============+=======+==============+
| aalType | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| eecid | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| capability | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| qosClass | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| bcob | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| stc | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| upcc | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| atmQOSparms | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| atmTrfcDesc | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| abrParms | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| abrSetup | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| bearerType | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| lij | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| anycast | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| cache | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| bearerSigIE | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aalApp | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| cbrRate | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| sbc | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| clkrec | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| fec | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| prtfl | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| structure | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| cpsSDUsize | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aal2CPS | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aal2CPSSDUrate | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aal2sscs3661unassured | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aal2sscs3661assured | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aal2sscs3662 | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aal5sscop | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| atmmap | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| silenceSupp | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| ecan | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| gc | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| profileDesc | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| vsel | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| dsel | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| fsel | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| onewaySel | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| codecconfig | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| isup_usi | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| uiLayer1_Prot | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| chain | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
Table 49: RFC 3108 Attribute Analysis
NOTE: RFC 3108 describes conventions for using SDP for characterizing
ATM bearer connections using an AAL1, AAL2, or AAL5 adaptation layer.
For AAL1, AAL2, and AAL5, bearer connections can be used to transport
single media streams. In addition, for AAL1 and AAL2, multiple media
streams can be multiplexed into a bearer connection. For all
adaptation types (AAL1, AAL2, and AAL5), bearer connections can be
bundled into a single media group. In all cases addressed by RFC
3108, a real-time media stream (voice, video, voiceband data,
pseudowire, and others) or a multiplex of media streams is mapped
directly into an ATM connection. RFC 3108 does not address cases
where ATM serves as a low-level transport pipe for IP packets that
can, in turn, carry one or more real-time (e.g., VoIP) media sessions
with a life cycle different from that of the underlying ATM
transport.
5.50. 3GPP TS 183.063
[TISPAN] describes Telecommunications and Internet converged Services
and Protocols for Advanced Networking (TISPAN);
+====================+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+====================+==============+=======+==============+
| PSCid | Not impacted | S | NORMAL |
+--------------------+--------------+-------+--------------+
| bc_service | Not impacted | S | NORMAL |
+--------------------+--------------+-------+--------------+
| bc_program | Not impacted | S | NORMAL |
+--------------------+--------------+-------+--------------+
| bc_service_package | Not impacted | S | NORMAL |
+--------------------+--------------+-------+--------------+
Table 50: 3GPP TS 183.063 Attribute Analysis
5.51. 3GPP TS 24.229
[IP-CALL] specifies an IP multimedia call control protocol based on
Session Initial protocol and Session Description Protocol.
+=================+============================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+=================+============================+=======+===========+
| secondary-realm | secondary-realm MUST be | M | TRANSPORT |
| | the one that corresponds | | |
| | to the "m=" line chosen | | |
| | for setting up the | | |
| | underlying transport flow. | | |
+-----------------+----------------------------+-------+-----------+
| visited-realm | visited-realm MUST be the | M | TRANSPORT |
| | one that corresponds to | | |
| | the "m=" line chosen for | | |
| | setting up the underlying | | |
| | transport flow. | | |
+-----------------+----------------------------+-------+-----------+
| omr-m-cksum | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
| omr-s-cksum | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
| omr-m-att | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
| omr-s-att | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
| omr-m-bw | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
| omr-s-bw | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
| omr-codecs | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
Table 51: 3GPP TS 24.229 Attribute Analysis
5.52. ITU T.38
[T.38] defines procedures for real-time Group 3 facsimile
communications over IP networks.
+=======================+=============+=======+==============+
| Name | Notes | Level | Mux Category |
+=======================+=============+=======+==============+
| T38FaxVersion | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38MaxBitRate | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxFillBitRemoval | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxTranscodingMMR | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxTranscodingJBIG | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxRateManagement | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxMaxBuffer | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxMaxDatagram | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxUdpEC | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxMaxIFP | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxUdpECDepth | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxUdpFECMaxSpan | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38ModemType | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38VendorInfo | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
Table 52: ITU T.38 Attribute Analysis
NOTE: As per Section 9 of [RFC8843], there exists no publicly
available specification that defines procedures for multiplexing/
demultiplexing fax protocol flows over a single 5-tuple. Once such a
specification is available, the multiplexing category assignments for
the attributes in this section could be revisited.
5.53. ITU-T Q.1970
[Q.1970] defines Bearer Independent Call Control (BICC) IP bearer
control protocol.
+=======+=====================================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+=======+=====================================+=======+==========+
| ipbcp | ipbcp version identifies the types | S | SPECIAL |
| | of IP bearer control protocol | | |
| | (IPBCP) message used in BICC (ITU-T | | |
| | Q.1901) environment that are | | |
| | limited to single-media payload. | | |
| | Refer to the pertinent ITU-T | | |
| | specifications while multiplexing. | | |
+-------+-------------------------------------+-------+----------+
Table 53: ITU-T Q.1970 Attribute Analysis
5.54. ITU-T H.248.15
ITU-T H.248.15 [H.248.15] defines the Gateway Control Protocol SDP
H.248 package attribute.
+==========+=====================================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+==========+=====================================+=======+==========+
| h248item | It is only applicable for | B | SPECIAL |
| | signaling the inclusion of H.248 | | |
| | extension packages to a gateway | | |
| | via the local and remote | | |
| | descriptors. The attribute | | |
| | itself is unaffected by | | |
| | multiplexing, but the package | | |
| | referenced in a specific use of | | |
| | the attribute can be impacted. | | |
| | Further analysis of each package | | |
| | is needed to determine if there | | |
| | is an issue. This is only a | | |
| | concern in environments using a | | |
| | decomposed server/gateway with | | |
| | H.248 signaled between them. The | | |
| | ITU-T will need to do further | | |
| | analysis of various packages when | | |
| | they specify how to signal the | | |
| | use of multiplexing to a gateway. | | |
+----------+-------------------------------------+-------+----------+
Table 54: ITU-T H.248.15 Attribute Analysis
5.55. RFC 4975: The Message Session Relay Protocol
[RFC4975] describes the Message Session Relay Protocol, a protocol
for transmitting a series of related instant messages in the context
of a session. Message sessions are treated like any other media
stream when set up via a rendezvous or session-creation protocol such
as the Session Initiation Protocol.
+======================+=============+=======+==============+
| Name | Notes | Level | Mux Category |
+======================+=============+=======+==============+
| accept-types | Refer to | M | TBD |
| | notes below | | |
+----------------------+-------------+-------+--------------+
| accept-wrapped-types | Refer to | M | TBD |
| | notes below | | |
+----------------------+-------------+-------+--------------+
| max-size | Refer to | M | TBD |
| | notes below | | |
+----------------------+-------------+-------+--------------+
| path | Refer to | M | TBD |
| | notes below | | |
+----------------------+-------------+-------+--------------+
Table 55: RFC 4975 Attribute Analysis
NOTE: As per Section 9 of [RFC8843], there exists no publicly
available specification that defines procedures for multiplexing/
demultiplexing MSRP flows over a single 5-tuple. Once such a
specification is available, the multiplexing categories assignments
for the attributes in this section could be revisited.
5.56. Historical Attributes
This section specifies analysis for the attributes that are included
for historic usage alone by the [IANA].
+=========+=====================+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+=====================+=======+==============+
| rtpred1 | Historic attributes | M | CAUTION |
+---------+---------------------+-------+--------------+
| rtpred2 | Historic attributes | M | CAUTION |
+---------+---------------------+-------+--------------+
Table 56: Historical Attribute Analysis
6. bwtype Attribute Analysis
This section specifies handling of specific bandwidth attributes when
used in multiplexing scenarios.
6.1. RFC 4566: SDP
[RFC4566] defines SDP that is intended for describing multimedia
sessions for the purposes of session announcement, session
invitation, and other forms of multimedia session initiation.
+===========+=================================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+===========+=================================+=======+==========+
| bwtype:CT | Not impacted | S | NORMAL |
+-----------+---------------------------------+-------+----------+
| bwtype:AS | For media-level usage, the | B | SUM |
| | aggregate of individual | | |
| | bandwidth values is considered. | | |
+-----------+---------------------------------+-------+----------+
Table 57: RFC 4566 bwtype Analysis
6.2. RFC 3556: SDP Bandwidth Modifiers for RTCP Bandwidth
[RFC3556] defines an extension to SDP to specify two additional
modifiers for the bandwidth attribute. These modifiers may be used
to specify the bandwidth allowed for RTCP packets in an RTP session.
+===========+================================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+===========+================================+=======+==========+
| bwtype:RS | Session-level usage represents | B | SUM |
| | session aggregate, and media- | | |
| | level usage indicates SUM of | | |
| | the individual values while | | |
| | multiplexing. | | |
+-----------+--------------------------------+-------+----------+
| bwtype:RR | Session-level usage represents | B | SUM |
| | session aggregate, and media- | | |
| | level usage indicates SUM of | | |
| | the individual values while | | |
| | multiplexing. | | |
+-----------+--------------------------------+-------+----------+
Table 58: RFC 3556 bwtype Analysis
6.3. RFC 3890: Bandwidth Modifier for SDP
[RFC3890] defines SDP Transport Independent Application Specific
Maximum (TIAS) bandwidth modifier that does not include transport
overhead; instead, an additional packet-rate attribute is defined.
The transport-independent bitrate value together with the maximum
packet rate can then be used to calculate the real bitrate over the
transport actually used.
+=============+==================================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+=============+==================================+=======+==========+
| bwtype:TIAS | The usage of TIAS is not | B | SPECIAL |
| | defined under offer/answer | | |
| | usage. | | |
+-------------+----------------------------------+-------+----------+
| maxprate | The usage of TIAS and | B | SPECIAL |
| | maxprate is not well | | |
| | defined under multiplexing. | | |
+-------------+----------------------------------+-------+----------+
Table 59: RFC 3890 bwtype Analysis
NOTE: The intention of TIAS is that the media-level bitrate is
multiplied with the known per-packet overhead for the selected
transport and the maxprate value to determine the worst-case bitrate
from the transport to more accurately capture the required usage.
Summing TIAS values independently across "m=" lines and multiplying
the computed sum with maxprate and the per-packet overhead would
inflate the value significantly. Instead, performing multiplication
and adding the individual values is a more appropriate usage.
7. rtcp-fb Attribute Analysis
This section analyzes rtcp-fb SDP attributes.
7.1. RFC 4585: RTP/AVPF
[RFC4585] defines an extension to the Audio-Visual Profile (AVP) that
enables receivers to provide, statistically, more immediate feedback
to the senders; it thus allows for short-term adaptation and
implementation of efficient feedback-based repair mechanisms.
+=========+=============================+=======+==================+
| Name | Notes | Level | Mux Category |
+=========+=============================+=======+==================+
| ack | The attribute value MUST be | M | IDENTICAL-PER-PT |
| rpsi | the same for a given codec | | |
| | configuration. | | |
+---------+-----------------------------+-------+------------------+
| ack app | Feedback parameters MUST be | M | SPECIAL |
| | handled in the app-specific | | |
| | way when multiplexed. | | |
+---------+-----------------------------+-------+------------------+
| nack | The attribute value MUST be | M | IDENTICAL-PER-PT |
| | the same for a given codec | | |
| | configuration. | | |
+---------+-----------------------------+-------+------------------+
| nack | The attribute value MUST be | M | IDENTICAL-PER-PT |
| pli | the same for a given codec | | |
| | configuration. | | |
+---------+-----------------------------+-------+------------------+
| nack | The attribute value MUST be | M | IDENTICAL-PER-PT |
| sli | the same for a given codec | | |
| | configuration. | | |
+---------+-----------------------------+-------+------------------+
| nack | The attribute value MUST be | M | IDENTICAL-PER-PT |
| rpsi | the same for a given codec | | |
| | configuration. | | |
+---------+-----------------------------+-------+------------------+
| nack | Feedback parameters MUST be | M | SPECIAL |
| app | handled in the app specific | | |
| | way when multiplexed. | | |
+---------+-----------------------------+-------+------------------+
| trr-int | The attribute value MUST be | M | IDENTICAL-PER-PT |
| | the same for a given codec | | |
| | configuration. | | |
+---------+-----------------------------+-------+------------------+
Table 60: RFC 4585 Attribute Analysis
7.2. RFC 5104: Codec Control Messages in AVPF
[RFC5104] specifies a few extensions to the messages defined in the
Audio-Visual Profile with Feedback (AVPF). They are helpful
primarily in conversational multimedia scenarios where centralized
multipoint functionalities are in use. However, some are also usable
in smaller multicast environments and point-to-point calls.
+======+==========================+=======+==================+
| Name | Notes | Level | Mux Category |
+======+==========================+=======+==================+
| ccm | The attribute value MUST | M | IDENTICAL-PER-PT |
| | be the same for a given | | |
| | codec configuration. | | |
+------+--------------------------+-------+------------------+
Table 61: RFC 5104 Attribute Analysis
7.3. RFC 6285: Unicast-Based Rapid Acquisition of Multicast RTP
Sessions (RAMS)
[RFC6285] describes a method of using the existing RTP and RTCP
machinery that reduces the acquisition delay. In this method, an
auxiliary unicast RTP session carrying the Reference Information to
the receiver precedes or accompanies the multicast stream. This
unicast RTP flow can be transmitted at a faster-than-natural bitrate
to further accelerate the acquisition. The motivating use case for
this capability is multicast applications that carry real-time
compressed audio and video.
+======+==========================+=======+==================+
| Name | Notes | Level | Mux Category |
+======+==========================+=======+==================+
| nack | The attribute value MUST | M | IDENTICAL-PER-PT |
| rai | be the same for a given | | |
| | codec configuration. | | |
+------+--------------------------+-------+------------------+
Table 62: RFC 6285 Attribute Analysis
7.4. RFC 6679: ECN for RTP over UDP/IP
[RFC6679] specifies how Explicit Congestion Notification (ECN) can be
used with the RTP running over UDP, using the RTCP as a feedback
mechanism. It defines a new RTCP Extended Report (XR) block for
periodic ECN feedback, a new RTCP transport feedback message for
timely reporting of congestion events, and a STUN extension used in
the optional initialization method using ICE.
+=================+============================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+=================+============================+=======+===========+
| ecn-capable-rtp | ECN markup is enabled at | M | IDENTICAL |
| | the RTP session level. | | |
+-----------------+----------------------------+-------+-----------+
| nack ecn | This attribute enables ECN | M | IDENTICAL |
| | at the RTP session level. | | |
+-----------------+----------------------------+-------+-----------+
Table 63: RFC 6679 Attribute Analysis
7.5. RFC 6642: Third-Party Loss Report
In a large RTP session using the RTCP feedback mechanism defined in
[RFC4585], a feedback target may experience transient overload if
some event causes a large number of receivers to send feedback at
once. This overload is usually avoided by ensuring that feedback
reports are forwarded to all receivers, allowing them to avoid
sending duplicate feedback reports. However, there are cases where
it is not recommended to forward feedback reports, and this may allow
feedback implosion. [RFC6642] discusses these cases and defines a
new RTCP Third-Party Loss Report that can be used to inform receivers
that the feedback target is aware of some loss event, allowing them
to suppress feedback. Associated SDP signaling is also defined.
+=======+==========================+=======+==================+
| Name | Notes | Level | Mux Category |
+=======+==========================+=======+==================+
| nack | The attribute value MUST | M | IDENTICAL-PER-PT |
| tllei | be the same for a given | | |
| | codec configuration. | | |
+-------+--------------------------+-------+------------------+
| nack | The attribute value MUST | M | IDENTICAL-PER-PT |
| pslei | be the same for a given | | |
| | codec configuration. | | |
+-------+--------------------------+-------+------------------+
Table 64: RFC 6642 Attribute Analysis
7.6. RFC 5104: Codec Control Messages in AVPF
[RFC5104] specifies a few extensions to the messages defined in the
Audio-Visual Profile with Feedback (AVPF). They are helpful
primarily in conversational multimedia scenarios where centralized
multipoint functionalities are in use. However, some are also usable
in smaller multicast environments and point-to-point calls.
+=======+==========================+=======+==================+
| Name | Notes | Level | Mux Category |
+=======+==========================+=======+==================+
| ccm | The attribute value MUST | M | IDENTICAL-PER-PT |
| fir | be the same for a given | | |
| | codec configuration. | | |
+-------+--------------------------+-------+------------------+
| ccm | The attribute value MUST | M | IDENTICAL-PER-PT |
| tmmbr | be the same for a given | | |
| | codec configuration. | | |
+-------+--------------------------+-------+------------------+
| ccm | The attribute value MUST | M | IDENTICAL-PER-PT |
| tstr | be the same for a given | | |
| | codec configuration. | | |
+-------+--------------------------+-------+------------------+
| ccm | The attribute value MUST | M | IDENTICAL-PER-PT |
| vbcm | be the same for a given | | |
| | codec configuration. | | |
+-------+--------------------------+-------+------------------+
Table 65: RFC 5104 Attribute Analysis
8. group Attribute Analysis
This section analyzes SDP "group" attribute semantics [RFC5888].
8.1. RFC 5888: SDP Grouping Framework
[RFC5888] defines a framework to group "m=" lines in SDP for
different purposes.
+===========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===========+==============+=======+==============+
| group:LS | Not impacted | S | NORMAL |
+-----------+--------------+-------+--------------+
| group:FID | Not impacted | S | NORMAL |
+-----------+--------------+-------+--------------+
Table 66: RFC 5888 Attribute Analysis
8.2. RFC 3524: Mapping Media Streams to Resource Reservation Flows
[RFC3524] defines an extension to the SDP grouping framework. It
allows requesting a group of media streams to be mapped into a single
resource reservation flow. The SDP syntax needed is defined, as well
as a new "semantics" attribute called Single Reservation Flow (SRF).
+===========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===========+==============+=======+==============+
| group:SRF | Not impacted | S | NORMAL |
+-----------+--------------+-------+--------------+
Table 67: RFC 3524 Attribute Analysis
8.3. RFC 4091: ANAT Semantics
[RFC4091] defines ANAT semantics for the SDP grouping framework.
(Note: [RFC4091] has been obsoleted by [RFC8445].) The ANAT
semantics allow alternative types of network addresses to establish a
particular media stream.
+============+==============================+=======+==============+
| Name | Notes | Level | Mux Category |
+============+==============================+=======+==============+
| group:ANAT | ANAT semantics is obsoleted. | S | CAUTION |
+------------+------------------------------+-------+--------------+
Table 68: RFC 4091 Attribute Analysis
8.4. RFC 5956: FEC Grouping Semantics in SDP
[RFC5956] defines the semantics for grouping the associated source
and FEC-based repair flows in SDP. The semantics defined in the
document are to be used with the SDP Grouping Framework [RFC5888].
These semantics allow the description of grouping relationships
between the source and repair flows when one or more source and/or
repair flows are associated in the same group; they also provide
support for additive repair flows. SSRC-level grouping semantics are
also defined in this document for RTP streams using SSRC
multiplexing.
+==============+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+==============+==============+=======+==============+
| group:FEC-FR | Not impacted | S | NORMAL |
+--------------+--------------+-------+--------------+
Table 69: RFC 5956 Attribute Analysis
8.5. RFC 5583: Signaling Media Decoding Dependency in SDP
[RFC5583] defines semantics that allow for signaling the decoding
dependency of different media descriptions with the same media type
in SDP. This is required, for example, if media data is separated
and transported in different network streams as a result of using a
layered or multiple descriptive media coding process.
+===========+==========================+=======+==================+
| Name | Notes | Level | Mux Category |
+===========+==========================+=======+==================+
| group:DDP | Not impacted | S | NORMAL |
+-----------+--------------------------+-------+------------------+
| depend | The attribute value MUST | M | IDENTICAL-PER-PT |
| lay | be the same for a given | | |
| | codec configuration. | | |
+-----------+--------------------------+-------+------------------+
| depend | The attribute value MUST | M | IDENTICAL-PER-PT |
| mdc | be the same for a given | | |
| | codec configuration. | | |
+-----------+--------------------------+-------+------------------+
Table 70: RFC 5583 Attribute Analysis
8.6. RFC 7104: Duplication Grouping Semantics in the SDP
[RFC7104] defines the semantics for grouping redundant streams in
SDP. The semantics defined in this document are to be used with the
SDP Grouping Framework. Grouping semantics at the synchronization
source (SSRC) level are also defined in this document for RTP streams
using SSRC multiplexing.
+===========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===========+==============+=======+==============+
| group:DUP | Not impacted | S | NORMAL |
+-----------+--------------+-------+--------------+
Table 71: RFC 7104 Attribute Analysis
9. ssrc-group Attribute Analysis
This section analyzes "ssrc-group" semantics.
9.1. RFC 5576: Source-Specific SDP Attributes
[RFC5576] defines a mechanism for describing RTP media sources --
which are identified by their synchronization source (SSRC)
identifiers -- in SDP, to associate attributes with these sources and
express relationships among sources. It also defines several source-
level attributes that can be used to describe properties of media
sources.
+===================+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===================+==============+=======+==============+
| ssrc-group:FID | Not impacted | SR | NORMAL |
+-------------------+--------------+-------+--------------+
| ssrc-group:FEC | Not impacted | SR | NORMAL |
+-------------------+--------------+-------+--------------+
| ssrc-group:FEC-FR | Not impacted | SR | NORMAL |
+-------------------+--------------+-------+--------------+
Table 72: RFC 5576 Attribute Analysis
9.2. RFC 7104: Duplication Grouping Semantics in the SDP
[RFC7104] defines the semantics for grouping redundant streams in
SDP. The semantics defined in this document are to be used with the
SDP Grouping Framework. Grouping semantics at the synchronization
source (SSRC) level are also defined in this document for RTP streams
using SSRC multiplexing.
+================+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+================+==============+=======+==============+
| ssrc-group:DUP | Not impacted | SR | NORMAL |
+----------------+--------------+-------+--------------+
Table 73: RFC 7104 Attribute Analysis
10. QoS Mechanism Token Analysis
This section analyzes QoS tokes specified with SDP.
10.1. RFC 5432: QoS Mechanism Selection in SDP
[RFC5432] defines procedures to negotiate QoS mechanisms using the
SDP offer/answer model.
+======+================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+======+================================+=======+===========+
| rsvp | rsvp attribute MUST be the one | B | TRANSPORT |
| | that corresponds to the "m=" | | |
| | line chosen for setting up the | | |
| | underlying transport flow. | | |
+------+--------------------------------+-------+-----------+
| nsis | rsvp attribute MUST be the one | B | TRANSPORT |
| | that corresponds to the "m=" | | |
| | line chosen for setting up the | | |
| | underlying transport. | | |
+------+--------------------------------+-------+-----------+
Table 74: RFC 5432 Attribute Analysis
NOTE: A single Differentiated Services Code Point (DSCP) for each
flow being multiplexed doesn't impact multiplexing, since QoS
mechanisms are signaled/scoped per flow. For scenarios that involve
having different DSCP code points for packets being transmitted over
the same 5-tuple, issues as discussed in [RFC7657] need to be taken
into consideration.
11. k= Attribute Analysis
11.1. RFC 4566: SDP
[RFC4566] defines SDP that is intended for describing multimedia
sessions for the purposes of session announcement, session
invitation, and other forms of multimedia session initiation.
+======+===================================+=======+==============+
| Name | Notes | Level | Mux Category |
+======+===================================+=======+==============+
| k= | It is not recommended to use this | S | CAUTION |
| | attribute under multiplexing. | | |
+------+-----------------------------------+-------+--------------+
Table 75: RFC 4566 Attribute Analysis
12. content Attribute Analysis
12.1. RFC 4796
[RFC4796] defines a new SDP media-level attribute, "content". The
"content" attribute defines the content of the media stream to a more
detailed level than the media description line. The sender of an SDP
session description can attach the "content" attribute to one or more
media streams. The receiving application can then treat each media
stream differently (e.g., show it on a big or small screen) based on
its content.
+=================+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+=================+==============+=======+==============+
| content:slides | Not impacted | M | NORMAL |
+-----------------+--------------+-------+--------------+
| content:speaker | Not impacted | M | NORMAL |
+-----------------+--------------+-------+--------------+
| content:main | Not impacted | M | NORMAL |
+-----------------+--------------+-------+--------------+
| content:sl | Not impacted | M | NORMAL |
+-----------------+--------------+-------+--------------+
| content:alt | Not impacted | M | NORMAL |
+-----------------+--------------+-------+--------------+
Table 76: RFC 4796 Attribute Analysis
12.2. 3GPP TS 24.182
[IMS-CAT] specifies an IP multimedia subsystem for customized
alerting tones.
+============+=========================+=======+==============+
| Name | Notes | Level | Mux Category |
+============+=========================+=======+==============+
| g.3gpp.cat | Usage defined for the | M | NORMAL |
| | IP multimedia subsystem | | |
+------------+-------------------------+-------+--------------+
Table 77: 3GPP TS 24.182 Attribute Analysis
12.3. 3GPP TS 24.183
[IMS-CRS] specifies an IP multimedia subsystem for customized ringing
signal.
+============+=========================+=======+==============+
| Name | Notes | Level | Mux Category |
+============+=========================+=======+==============+
| g.3gpp.crs | Usage defined for the | M | NORMAL |
| | IP multimedia subsystem | | |
+------------+-------------------------+-------+--------------+
Table 78: 3GPP TS 24.183 Attribute Analysis
13. Payload Formats
13.1. RFC 5109: RTP Payload Format for Generic FEC
[RFC5109] describes a payload format for generic Forward Error
Correction (FEC) for media data encapsulated in RTP. It is based on
the exclusive-or (parity) operation. The payload format allows end
systems to apply protection using various protection lengths and
levels, in addition to using various protection group sizes to adapt
to different media and channel characteristics. It enables complete
recovery of the protected packets or partial recovery of the critical
parts of the payload, depending on the packet loss situation.
+==============+=====================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+==============+=====================+=======+==========+
| audio/ulpfec | Not recommended for | M | CAUTION |
| | multiplexing due to | | |
| | reuse of SSRCs. | | |
+--------------+---------------------+-------+----------+
| video/ulpfec | Not recommended for | M | CAUTION |
| | multiplexing due to | | |
| | reuse of SSRCs. | | |
+--------------+---------------------+-------+----------+
| text/ulpfec | Not recommended for | M | CAUTION |
| | multiplexing due to | | |
| | reuse of SSRCs. | | |
+--------------+---------------------+-------+----------+
| application/ | Not recommended for | M | CAUTION |
| ulpfec | multiplexing due to | | |
| | reuse of SSRCs. | | |
+--------------+---------------------+-------+----------+
Table 79: RFC 5109 Payload Format Analysis
14. Multiplexing Considerations for Encapsulating Attributes
This section deals with recommendations for defining the multiplexing
characteristics of the SDP attributes that encapsulate other SDP
attributes/parameters. As of today, such attributes, for example,
are defined in [RFC3407], [RFC5939] and [RFC6871] as part of a
generic framework for indicating and negotiating transport-, media-,
and media-format-related capabilities in the SDP.
The behavior of such attributes under multiplexing is, in turn,
defined by the multiplexing behavior of the attributes they
encapsulate, which are made known once the offer/answer negotiation
process is completed.
14.1. RFC 3407: cpar Attribute Analysis
The [RFC3407] capability parameter attribute "a=cpar" encapsulates a
"b=" (bandwidth) or an "a=" attribute. For bandwidth attribute
encapsulation, the category SUM is inherited. For the case of "a="
attribute, the category corresponding to the SDP attribute being
encapsulated is inherited.
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
m=video 3456 RTP/AVP 100
a=rtpmap:100 VP8/90000
a=sqn: 0
a=cdsc: 1 video RTP/AVP 100
a=cpar: a=rtcp-mux
m=video 3456 RTP/AVP 101
a=rtpmap:101 VP8/90000
a=fmtp:100 max-fr=15;max-fs=1200
a=cdsc: 2 video RTP/AVP 101
a=cpar: a=rtcp-mux
In this example, the category IDENTICAL is inherited for the cpar-
encapsulated "rtcp-mux" attribute.
14.2. RFC 5939 Analysis
[RFC5939] defines a general SDP capability negotiation framework. It
also specifies how to provide transport protocols and SDP attributes
as capabilities and negotiate them using the framework.
For this purpose, [RFC5939] defines the following:
* A set of capabilities for the session and its associated media-
stream components, supported by each side. The attribute "a=acap"
defines how to list an attribute name and its associated value (if
any) as a capability. The attribute "a=tcap" defines how to list
transport protocols (e.g., "RTP/AVP") as capabilities.
* A set of potential configurations ("a=pcfg") provided by the
offerer to indicate which combinations of those capabilities can
be used for the session and its associated media stream
components. Potential configurations are not ready for use until
fully negotiated. They provide an alternative that MAY be used,
subject to SDP capability-negotiation procedures. In particular,
the answerer MAY choose one of the potential configurations for
use as part of the current offer/answer exchange.
* An actual configuration ("a=acfg") for the session and its
associated media stream components. The actual configuration
identifies the potential configuration that was negotiated for
use. Use of an actual configuration does not require any further
negotiation.
* A negotiation process that takes the current actual and the set of
potential configurations (combinations of capabilities) as input
and provides the negotiated actual configurations as output. In
[RFC5939], the negotiation process is done independently for each
media description.
14.2.1. Recommendation: Procedures for Potential Configuration Pairing
This section provides recommendations for entities generating and
processing SDP under the generic capability-negotiation framework as
defined in [RFC5939] under the context of media-stream multiplexing.
These recommendations are provided for the purposes of enabling the
offerer to make sure that the generated potential configurations
between the multiplexed streams can (easily) be negotiated to be
consistent between those streams. In particular, the procedures aim
to simplify the answerer's procedure for choosing potential
configurations that are consistent across all the multiplexed media
descriptions.
A potential configuration selects a set of attributes and parameters
that become part of the media description when negotiated. When
multiplexing media descriptions with potential configurations
specified, there MAY be a need for coordinating this selection
between multiplexed media descriptions to ensure the right
multiplexing behavior.
Although it is possible to analyze the various potential
configurations in multiplexed media descriptions to find combinations
that satisfy such constraints, it can quickly become complicated to
do so.
The procedures defined in [RFC5939] state that each potential
configuration in the SDP has a unique configuration number; however,
the scope of uniqueness is limited to each media description. To
make it simple for the answerer to chose valid combinations of
potential configurations across media descriptions in a given BUNDLE
group, we provide a simple rule for constructing potential
configurations:
* Let m-bundle be the set of media descriptions that form a given
bundle.
* Let m-bundle-pcfg be the set of media descriptions in m-bundle
that include one or more potential configurations.
* Each media description in m-bundle-pcfg MUST have at least one
potential configuration with the same configuration number (e.g.,
"1").
* For each potential configuration with configuration number x in m-
bundle-pcfg, the offerer MUST ensure that if the answerer chooses
configuration number x in each of the media descriptions in m-
bundle-pcfg, then the resulting SDP will have all multiplexing
constraints satisfied for those media descriptions.
* Since it is nearly impossible to define a generic mechanism for
various capability extensions, this document doesn't provide
procedures for dealing with the capability-extension attributes.
However, Section 14.3 provides analysis of media-capability-
extension attributes as defined in [RFC6871].
The above allows the answerer to easily find multiplexing-compatible
combinations of potential configurations. The answerer simply
chooses a potential configuration (number) that is present in all of
the media descriptions with potential configurations in the bundle.
Note that it is still possible for the offerer to provide additional
potential configurations with independent configuration numbers. The
answerer will have to perform more complicated analysis to determine
valid multiplexed combinations of those.
14.2.1.1. Example: Transport-Capability Multiplexing
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
a=tcap:1 RTP/SAVPF
a=tcap:2 RTP/SAVP
a=group:BUNDLE audio video
m=audio
a=mid:audio
a=pcfg:1 t=1
a=pcfg:2
m=video
a=mid:video
a=pcfg:1 t=1
a=pcfg:2 t=2
In this example, the potential configurations that offer transport-
protocol capability of RTP/SAVPF have the same configuration number
"1" in both the audio and video media descriptions.
14.2.1.2. Example: Attribute-Capability Multiplexing
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
a=acap:1 a=rtcp-mux
a=acap:2 a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:EcGZiNWpFJhQXdspcl1ekcmVCNWpVLcfHAwJSoj|2^20|1:32
a=group:BUNDLE audio video
m=audio 49172 RTP/AVP 99
a=mid:audio
a=pcfg:1 a=1
a=pcfg:2
m=video 560024 RTP/AVP 100
a=mid:video
a=pcfg:1 a=1
a=pcfg:2 a=2
In this example, the potential configuration number "1" is repeated
while referring to attribute capability a=rtcp-mux, since the
behavior is IDENTICAL for the attribute a=rtcp-mux under
multiplexing.
14.3. RFC 6871 Analysis
[RFC6871] extends the capability negotiation framework described in
[RFC5939] by defining media capabilities that can be used to indicate
and negotiate media types and their associated format parameters. It
also allows indication of latent configurations and session
capabilities.
14.3.1. Recommendation: Dealing with Payload Type Numbers
[RFC6871] defines a new payload type parameter ("pt") to be used with
the potential, actual, and latent configuration parameters. The
parameter associates RTP payload type numbers with the referenced
RTP-based media-format capabilities ("a=rmcap") defined in [RFC6871]
and is appropriate only when the transport protocol uses RTP. This
means that the same payload type number can be assigned as part of
potential or actual configurations in different media descriptions in
a bundle. There are rules for the usage of identical payload type
values across multiplexed "m=" lines, described in [RFC8843], which
must be followed here, as well. As described in Section 14.2.1, the
use of identical configuration numbers for compatible configurations
in different media descriptions that are part of the bundle provides
a way to ensure that the answerer can easily pick compatible
configurations here, as well.
14.3.1.1. Example: Attribute Capability under Shared Payload Type
The attributes "a=rmcap" and "a=mfcap" follow the above
recommendations under multiplexing.
v=0
o=- 25678 753849 IN IP4 192.0.2.1
s=
c=IN IP4 192.0.2.1
t=0 0
a=creq:med-v0
m=audio 54322 RTP/AVP 96
a=rtpmap:96 AMR-WB/16000/1
a=fmtp:96 mode-change-capability=1; max-red=220;
mode-set=0,2,4,7
a=rmcap:1,3 audio AMR-WB/16000/1
a=rmcap:2 audio AMR/8000/1
a=mfcap:1,2 mode-change-capability=1
a=mfcap:3 mode-change-capability=2
a=pcfg:1 m=1 pt=1:96
a=pcfg:2 m=2 pt=2:97
a=pcfg:3 m=3 pt=3:98
m=audio 54322 RTP/AVP 96
a=rtpmap:96 AMR-WB/16000/1
a=fmtp:96 mode-change-capability=1; max-red=220;
mode-set=0,2,4,7
a=rmcap:4 audio AMR/8000/1
a=rmcap:5 audio OPUS/48000/2
a=mfcap:5 minptime=40
a=mfcap:4 mode-change-capability=1
a=pcfg:1 m=4 pt=4:97
a=pcfg:4 m=5 pt=5:101
In this example, the potential configuration number "1" is repeated
when referring to media and media-format capability used for the
Payload Type 96. This implies that both media capabilities 2 and 4,
along with their media-format capabilities, MUST refer to the same
codec configuration, as per the definition of IDENTICAL-PER-PT.
14.3.2. Recommendation: Dealing with Latent Configurations
[RFC6871] adds the notion of a latent configuration that provides
configuration information that may be used to guide a subsequent
offer/exchange -- e.g., by adding another media stream or using
alternative codec combinations not currently offered. Latent
configurations have configuration numbers that cannot overlap with
the potential configuration numbers [RFC6871]. Supported
combinations of potential and latent configurations are indicated by
use of the "a=sescap" attribute; however, use of this attribute is
not recommended with multiplexed media, since it requires the use of
unique configuration numbers across the SDP. Taken together, this
means there is no well-defined way to indicate supported combinations
of latent configurations, or combinations of latent and potential
configurations with multiplexed media. It is still allowed to use
the latent configuration attribute; however, the limitations above
will apply. To determine valid combinations, actual negotiation will
have to be attempted subsequently instead.
15. IANA Considerations
Section 15.1 defines a new subregistry, which has been added by the
IANA, for identifying the initial registrations for various
multiplexing categories applicable, as described in this document.
IANA has added a new column named "Mux Category" to several of the
subregistries in the "Session Description Protocol (SDP) Parameters"
registry. The tables in Section 15.2 identify the names of entries
in the existing subregistry and specify the value to be put in the
new "Mux Category" column of the associated IANA registry for each.
15.1. New "Multiplexing Categories" Subregistry
A new subregistry has been created. It is called "Multiplexing
Categories" and has the following registrations initially:
+=========================+===========+
| Multiplexing Categories | Reference |
+=========================+===========+
| NORMAL | RFC 8859 |
+-------------------------+-----------+
| CAUTION | RFC 8859 |
+-------------------------+-----------+
| IDENTICAL | RFC 8859 |
+-------------------------+-----------+
| TRANSPORT | RFC 8859 |
+-------------------------+-----------+
| SUM | RFC 8859 |
+-------------------------+-----------+
| INHERIT | RFC 8859 |
+-------------------------+-----------+
| IDENTICAL-PER-PT | RFC 8859 |
+-------------------------+-----------+
| SPECIAL | RFC 8859 |
+-------------------------+-----------+
| TBD | RFC 8859 |
+-------------------------+-----------+
Table 80
Further entries can be registered using Standard Actions policies
outlined in [RFC8126], which requires IESG review and approval and
Standards Track IETF RFC publication.
Each registration needs to indicate the multiplexing category value
to be added to the "Multiplexing Categories" subregistry, as defined
in this section.
Such a registration MUST also indicate the applicability of the newly
defined multiplexing category value to various subregistries defined
in the "Session Description Protocol (SDP) Parameters" registry.
15.2. "Mux Category" Column for Subregistries
Each subsection identifies a subregistry of the "Session Description
Protocol (SDP) Parameters" registry. The tables list the column that
identifies the SDP attribute name/Token/Value from the corresponding
subregistries and the values to be used for the new "Mux Category"
column to be added.
Entries in the existing subregistries of the "Session Description
Protocol (SDP) Parameters" registry that lack a value for the "Mux
Category" in this specification will get a value of "TBD".
The registration policy for updates to the "Mux Category" column
values for existing parameters, or when registering new parameters,
is beyond the scope of this document. The registration policy for
the affected table is defined in [RFC8866].
15.2.1. Table: SDP bwtype
The following values have been added to the "bwtype" subregistry of
the "Session Description Protocol (SDP) Parameters" registry. The
references have been updated to point to this RFC as well as the
previous references.
+==========+==============+
| SDP Name | Mux Category |
+==========+==============+
| CT | NORMAL |
+----------+--------------+
| AS | SUM |
+----------+--------------+
| RS | SUM |
+----------+--------------+
| RR | SUM |
+----------+--------------+
| TIAS | SPECIAL |
+----------+--------------+
Table 81
15.2.2. Table: attribute-name
The following values have been added to the "attribute-name"
(formerly "att-field") subregistry of the "Session Description
Protocol (SDP) Parameters" registry. The references have been
updated to point to this RFC as well as the previous references.
NOTE: The attributes from [FLUTE] ("flute-tsi", "flute-ch", "FEC-
declaration", "FEC-OTI-extension", "content-desc") were not analyzed
for their multiplexing behavior, due to the expired status of the
draft. For the purposes of this specification, the multiplexing
category of "TBD" is assigned.
+==========================+==================+
| SDP Name | Mux Category |
+==========================+==================+
| cat | NORMAL |
+--------------------------+------------------+
| keywds | NORMAL |
+--------------------------+------------------+
| type | NORMAL |
+--------------------------+------------------+
| type:broadcast | NORMAL |
+--------------------------+------------------+
| type:H332 | NORMAL |
+--------------------------+------------------+
| type:meeting | NORMAL |
+--------------------------+------------------+
| type:moderated | NORMAL |
+--------------------------+------------------+
| type:test | NORMAL |
+--------------------------+------------------+
| charset | NORMAL |
+--------------------------+------------------+
| charset:iso8895-1 | NORMAL |
+--------------------------+------------------+
| tool | NORMAL |
+--------------------------+------------------+
| ipbcp | SPECIAL |
+--------------------------+------------------+
| group | NORMAL |
+--------------------------+------------------+
| ice-lite | NORMAL |
+--------------------------+------------------+
| ice-options | NORMAL |
+--------------------------+------------------+
| bcastversion | NORMAL |
+--------------------------+------------------+
| 3GPP-Integrity-Key | CAUTION |
+--------------------------+------------------+
| 3GPP-SDP-Auth | CAUTION |
+--------------------------+------------------+
| alt-group | CAUTION |
+--------------------------+------------------+
| PSCid | NORMAL |
+--------------------------+------------------+
| bc_service | NORMAL |
+--------------------------+------------------+
| bc_program | NORMAL |
+--------------------------+------------------+
| bc_service_package | NORMAL |
+--------------------------+------------------+
| sescap | CAUTION |
+--------------------------+------------------+
| rtsp-ice-d-m | TBD |
+--------------------------+------------------+
| recvonly | NORMAL |
+--------------------------+------------------+
| sendrecv | NORMAL |
+--------------------------+------------------+
| sendonly | NORMAL |
+--------------------------+------------------+
| sdplang | NORMAL |
+--------------------------+------------------+
| lang | NORMAL |
+--------------------------+------------------+
| h248item | SPECIAL |
+--------------------------+------------------+
| sqn | NORMAL |
+--------------------------+------------------+
| cdsc | NORMAL |
+--------------------------+------------------+
| cpar | INHERIT |
+--------------------------+------------------+
| cparmin | SPECIAL |
+--------------------------+------------------+
| cparmax | SPECIAL |
+--------------------------+------------------+
| rtcp-xr | NORMAL |
+--------------------------+------------------+
| maxprate | SPECIAL |
+--------------------------+------------------+
| setup | TRANSPORT |
+--------------------------+------------------+
| connection | TRANSPORT |
+--------------------------+------------------+
| key-mgmt | IDENTICAL |
+--------------------------+------------------+
| source-filter | IDENTICAL |
+--------------------------+------------------+
| inactive | NORMAL |
+--------------------------+------------------+
| fingerprint | TRANSPORT |
+--------------------------+------------------+
| flute-tsi | TBD |
+--------------------------+------------------+
| flute-ch | TBD |
+--------------------------+------------------+
| FEC-declaration | TBD |
+--------------------------+------------------+
| FEC-OTI-extension | TBD |
+--------------------------+------------------+
| content-desc | TBD |
+--------------------------+------------------+
| ice-pwd | TRANSPORT |
+--------------------------+------------------+
| ice-ufrag | TRANSPORT |
+--------------------------+------------------+
| stkmstream | NORMAL |
+--------------------------+------------------+
| extmap | SPECIAL |
+--------------------------+------------------+
| qos-mech-send | TRANSPORT |
+--------------------------+------------------+
| qos-mech-recv | TRANSPORT |
+--------------------------+------------------+
| csup | NORMAL |
+--------------------------+------------------+
| creq | NORMAL |
+--------------------------+------------------+
| acap | INHERIT |
+--------------------------+------------------+
| tcap | INHERIT |
+--------------------------+------------------+
| 3GPP-QoE-Metrics | CAUTION |
+--------------------------+------------------+
| 3GPP-Asset-Information | CAUTION |
+--------------------------+------------------+
| mbms-mode | CAUTION |
+--------------------------+------------------+
| mbms-repair | CAUTION |
+--------------------------+------------------+
| ike-setup | IDENTICAL |
+--------------------------+------------------+
| psk-fingerprint | IDENTICAL |
+--------------------------+------------------+
| multicast-rtcp | IDENTICAL |
+--------------------------+------------------+
| rmcap | IDENTICAL-PER-PT |
+--------------------------+------------------+
| omcap | NORMAL |
+--------------------------+------------------+
| mfcap | IDENTICAL-PER-PT |
+--------------------------+------------------+
| mscap | INHERIT |
+--------------------------+------------------+
| 3gpp.iut.replication | TBD |
+--------------------------+------------------+
| bcap | INHERIT |
+--------------------------+------------------+
| ccap | IDENTICAL |
+--------------------------+------------------+
| icap | NORMAL |
+--------------------------+------------------+
| etag | CAUTION |
+--------------------------+------------------+
| duplication-delay | NORMAL |
+--------------------------+------------------+
| range | CAUTION |
+--------------------------+------------------+
| control | CAUTION |
+--------------------------+------------------+
| mtag | CAUTION |
+--------------------------+------------------+
| ts-refclk | NORMAL |
+--------------------------+------------------+
| mediaclk | NORMAL |
+--------------------------+------------------+
| calgextmap | NORMAL |
+--------------------------+------------------+
| ptime | IDENTICAL-PER-PT |
+--------------------------+------------------+
| orient | NORMAL |
+--------------------------+------------------+
| orient:portrait | NORMAL |
+--------------------------+------------------+
| orient:landscape | NORMAL |
+--------------------------+------------------+
| orient:seascape | NORMAL |
+--------------------------+------------------+
| framerate | IDENTICAL-PER-PT |
+--------------------------+------------------+
| quality | NORMAL |
+--------------------------+------------------+
| rtpmap | IDENTICAL-PER-PT |
+--------------------------+------------------+
| fmtp | IDENTICAL-PER-PT |
+--------------------------+------------------+
| rtpred1 | CAUTION |
+--------------------------+------------------+
| rtpred2 | CAUTION |
+--------------------------+------------------+
| T38FaxVersion | TBD |
+--------------------------+------------------+
| T38MaxBitRate | TBD |
+--------------------------+------------------+
| T38FaxFillBitRemoval | TBD |
+--------------------------+------------------+
| T38FaxTranscodingMMR | TBD |
+--------------------------+------------------+
| T38FaxTranscodingJBIG | TBD |
+--------------------------+------------------+
| T38FaxRateManagement | TBD |
+--------------------------+------------------+
| T38FaxMaxBuffer | TBD |
+--------------------------+------------------+
| T38FaxMaxDatagram | TBD |
+--------------------------+------------------+
| T38FaxUdpEC | TBD |
+--------------------------+------------------+
| maxptime | IDENTICAL-PER-PT |
+--------------------------+------------------+
| des | CAUTION |
+--------------------------+------------------+
| curr | CAUTION |
+--------------------------+------------------+
| conf | CAUTION |
+--------------------------+------------------+
| mid | NORMAL |
+--------------------------+------------------+
| rtcp | TRANSPORT |
+--------------------------+------------------+
| rtcp-fb | IDENTICAL-PER-PT |
+--------------------------+------------------+
| label | NORMAL |
+--------------------------+------------------+
| T38VendorInfo | TBD |
+--------------------------+------------------+
| crypto | TRANSPORT |
+--------------------------+------------------+
| eecid | CAUTION |
+--------------------------+------------------+
| aalType | CAUTION |
+--------------------------+------------------+
| capability | CAUTION |
+--------------------------+------------------+
| qosClass | CAUTION |
+--------------------------+------------------+
| bcob | CAUTION |
+--------------------------+------------------+
| stc | CAUTION |
+--------------------------+------------------+
| upcc | CAUTION |
+--------------------------+------------------+
| atmQOSparms | CAUTION |
+--------------------------+------------------+
| atmTrfcDesc | CAUTION |
+--------------------------+------------------+
| abrParms | CAUTION |
+--------------------------+------------------+
| abrSetup | CAUTION |
+--------------------------+------------------+
| bearerType | CAUTION |
+--------------------------+------------------+
| lij | CAUTION |
+--------------------------+------------------+
| anycast | CAUTION |
+--------------------------+------------------+
| cache | CAUTION |
+--------------------------+------------------+
| bearerSigIE | CAUTION |
+--------------------------+------------------+
| aalApp | CAUTION |
+--------------------------+------------------+
| cbrRate | CAUTION |
+--------------------------+------------------+
| sbc | CAUTION |
+--------------------------+------------------+
| clkrec | CAUTION |
+--------------------------+------------------+
| fec | CAUTION |
+--------------------------+------------------+
| prtfl | CAUTION |
+--------------------------+------------------+
| structure | CAUTION |
+--------------------------+------------------+
| cpsSDUsize | CAUTION |
+--------------------------+------------------+
| aal2CPS | CAUTION |
+--------------------------+------------------+
| aal2CPSSDUrate | CAUTION |
+--------------------------+------------------+
| aal2sscs3661unassured | CAUTION |
+--------------------------+------------------+
| aal2sscs3661assured | CAUTION |
+--------------------------+------------------+
| aal2sscs3662 | CAUTION |
+--------------------------+------------------+
| aal5sscop | CAUTION |
+--------------------------+------------------+
| atmmap | CAUTION |
+--------------------------+------------------+
| silenceSupp | CAUTION |
+--------------------------+------------------+
| ecan | CAUTION |
+--------------------------+------------------+
| gc | CAUTION |
+--------------------------+------------------+
| profileDesc | CAUTION |
+--------------------------+------------------+
| vsel | CAUTION |
+--------------------------+------------------+
| dsel | CAUTION |
+--------------------------+------------------+
| fsel | CAUTION |
+--------------------------+------------------+
| onewaySel | CAUTION |
+--------------------------+------------------+
| codecconfig | CAUTION |
+--------------------------+------------------+
| isup_usi | CAUTION |
+--------------------------+------------------+
| uiLayer1_Prot | CAUTION |
+--------------------------+------------------+
| chain | CAUTION |
+--------------------------+------------------+
| floorctrl | TBD |
+--------------------------+------------------+
| confid | TBD |
+--------------------------+------------------+
| userid | TBD |
+--------------------------+------------------+
| floorid | TBD |
+--------------------------+------------------+
| FEC | NORMAL |
+--------------------------+------------------+
| accept-types | TBD |
+--------------------------+------------------+
| accept-wrapped-types | TBD |
+--------------------------+------------------+
| max-size | TBD |
+--------------------------+------------------+
| path | TBD |
+--------------------------+------------------+
| dccp-service-code | CAUTION |
+--------------------------+------------------+
| rtcp-mux | IDENTICAL |
+--------------------------+------------------+
| candidate | TRANSPORT |
+--------------------------+------------------+
| ice-mismatch | NORMAL |
+--------------------------+------------------+
| remote-candidates | TRANSPORT |
+--------------------------+------------------+
| SRTPAuthentication | TBD |
+--------------------------+------------------+
| SRTPROCTxRate | TBD |
+--------------------------+------------------+
| rtcp-rsize | IDENTICAL |
+--------------------------+------------------+
| file-selector | TBD |
+--------------------------+------------------+
| file-transfer-id | TBD |
+--------------------------+------------------+
| file-disposition | TBD |
+--------------------------+------------------+
| file-date | TBD |
+--------------------------+------------------+
| file-icon | TBD |
+--------------------------+------------------+
| file-range | TBD |
+--------------------------+------------------+
| depend | IDENTICAL-PER-PT |
+--------------------------+------------------+
| ssrc | NORMAL |
+--------------------------+------------------+
| ssrc-group | NORMAL |
+--------------------------+------------------+
| rtcp-unicast | IDENTICAL |
+--------------------------+------------------+
| pcfg | SPECIAL |
+--------------------------+------------------+
| acfg | SPECIAL |
+--------------------------+------------------+
| zrtp-hash | TRANSPORT |
+--------------------------+------------------+
| X-predecbufsize | CAUTION |
+--------------------------+------------------+
| X-initpredecbufperiod | CAUTION |
+--------------------------+------------------+
| X-initpostdecbufperiod | CAUTION |
+--------------------------+------------------+
| X-decbyterate | CAUTION |
+--------------------------+------------------+
| 3gpp-videopostdecbufsize | CAUTION |
+--------------------------+------------------+
| framesize | CAUTION |
+--------------------------+------------------+
| 3GPP-SRTP-Config | CAUTION |
+--------------------------+------------------+
| alt | CAUTION |
+--------------------------+------------------+
| alt-default-id | CAUTION |
+--------------------------+------------------+
| 3GPP-Adaption-Support | CAUTION |
+--------------------------+------------------+
| mbms-flowid | CAUTION |
+--------------------------+------------------+
| fec-source-flow | SPECIAL |
+--------------------------+------------------+
| fec-repair-flow | SPECIAL |
+--------------------------+------------------+
| repair-window | SPECIAL |
+--------------------------+------------------+
| rams-updates | CAUTION |
+--------------------------+------------------+
| imageattr | IDENTICAL-PER-PT |
+--------------------------+------------------+
| cfw-id | NORMAL |
+--------------------------+------------------+
| portmapping-req | CAUTION |
+--------------------------+------------------+
| ecn-capable-rtp | IDENTICAL |
+--------------------------+------------------+
| visited-realm | TRANSPORT |
+--------------------------+------------------+
| secondary-realm | TRANSPORT |
+--------------------------+------------------+
| omr-s-cksum | NORMAL |
+--------------------------+------------------+
| omr-m-cksum | NORMAL |
+--------------------------+------------------+
| omr-codecs | NORMAL |
+--------------------------+------------------+
| omr-m-att | NORMAL |
+--------------------------+------------------+
| omr-s-att | NORMAL |
+--------------------------+------------------+
| omr-m-bw | NORMAL |
+--------------------------+------------------+
| omr-s-bw | NORMAL |
+--------------------------+------------------+
| msrp-cema | TBD |
+--------------------------+------------------+
| dccp-port | CAUTION |
+--------------------------+------------------+
| resource | NORMAL |
+--------------------------+------------------+
| channel | NORMAL |
+--------------------------+------------------+
| cmid | NORMAL |
+--------------------------+------------------+
| content | NORMAL |
+--------------------------+------------------+
| lcfg | SPECIAL |
+--------------------------+------------------+
| loopback | NORMAL |
+--------------------------+------------------+
| loopback-source | NORMAL |
+--------------------------+------------------+
| loopback-mirror | NORMAL |
+--------------------------+------------------+
| chatroom | TBD |
+--------------------------+------------------+
| altc | TRANSPORT |
+--------------------------+------------------+
| T38FaxMaxIFP | TBD |
+--------------------------+------------------+
| T38FaxUdpECDepth | TBD |
+--------------------------+------------------+
| T38FaxUdpFECMaxSpan | TBD |
+--------------------------+------------------+
| T38ModemType | TBD |
+--------------------------+------------------+
| cs-correlation | TBD |
+--------------------------+------------------+
| rtcp-idms | NORMAL |
+--------------------------+------------------+
| cname | NORMAL |
+--------------------------+------------------+
| previous-ssrc | NORMAL |
+--------------------------+------------------+
| fmtp | IDENTICAL-PER-PT |
+--------------------------+------------------+
| ts-refclk | NORMAL |
+--------------------------+------------------+
| mediaclk | NORMAL |
+--------------------------+------------------+
Table 82
15.2.3. Table: content SDP Parameters
The following values have been added to the "content SDP Parameters"
subregistry of the "Session Description Protocol (SDP) Parameters"
registry. The references have been updated to point to this RFC as
well as the previous references.
+============+==============+
| SDP Name | Mux Category |
+============+==============+
| slides | NORMAL |
+------------+--------------+
| speaker | NORMAL |
+------------+--------------+
| sl | NORMAL |
+------------+--------------+
| main | NORMAL |
+------------+--------------+
| alt | NORMAL |
+------------+--------------+
| g.3gpp.cat | NORMAL |
+------------+--------------+
| g.3gpp.crs | NORMAL |
+------------+--------------+
Table 83
15.2.4. Table: Semantics for the "group" SDP Attribute
The following values have been added to the "Semantics for the
'group' SDP Attribute" subregistry of the "Session Description
Protocol (SDP) Parameters" registry. The references have been
updated to point to this RFC as well as the previous references.
+========+==============+
| Token | Mux Category |
+========+==============+
| LS | NORMAL |
+--------+--------------+
| FID | NORMAL |
+--------+--------------+
| SRF | NORMAL |
+--------+--------------+
| ANAT | CAUTION |
+--------+--------------+
| FEC | NORMAL |
+--------+--------------+
| FEC-FR | NORMAL |
+--------+--------------+
| CS | NORMAL |
+--------+--------------+
| DDP | NORMAL |
+--------+--------------+
| DUP | NORMAL |
+--------+--------------+
Table 84
15.2.5. Table: "rtcp-fb" Attribute Values
The following values have been added to the "'rtcp-fb' Attribute
Values" subregistry of the "Session Description Protocol (SDP)
Parameters" registry. The references have been updated to point to
this RFC as well as the previous references.
+============+==================+
| Value Name | Mux Category |
+============+==================+
| ack | IDENTICAL-PER-PT |
+------------+------------------+
| app | SPECIAL |
+------------+------------------+
| ccm | IDENTICAL-PER-PT |
+------------+------------------+
| nack | IDENTICAL-PER-PT |
+------------+------------------+
| trr-int | IDENTICAL-PER-PT |
+------------+------------------+
Table 85
15.2.6. Table: "ack" and "nack" Attribute Values
The following values have been added to the "'ack' and 'nack'
Attribute Values" subregistry of the "Session Description Protocol
(SDP) Parameters" registry. The references have been updated to
point to this RFC as well as the previous references.
+============+==================+
| Value Name | Mux Category |
+============+==================+
| sli | IDENTICAL-PER-PT |
+------------+------------------+
| pli | IDENTICAL-PER-PT |
+------------+------------------+
| rpsi | IDENTICAL-PER-PT |
+------------+------------------+
| app | SPECIAL |
+------------+------------------+
| rai | IDENTICAL-PER-PT |
+------------+------------------+
| tllei | IDENTICAL-PER-PT |
+------------+------------------+
| pslei | IDENTICAL-PER-PT |
+------------+------------------+
| ecn | IDENTICAL |
+------------+------------------+
Table 86
15.2.7. Table: "depend" SDP Attribute Values
The following values have been added to the "'depend' SDP Attribute
Values" subregistry of the "Session Description Protocol (SDP)
Parameters" registry. The references have been updated to point to
this RFC as well as the previous references.
+=======+==================+
| Token | Mux Category |
+=======+==================+
| lay | IDENTICAL-PER-PT |
+-------+------------------+
| mdc | IDENTICAL-PER-PT |
+-------+------------------+
Table 87
15.2.8. Table: "cs-correlation" Attribute Values
The following values have been added to the "'cs-correlation'
Attribute Values" subregistry of the "Session Description Protocol
(SDP) Parameters" registry. The references have been updated to
point to this RFC as well as the previous references.
+==========+==============+
| Value | Mux Category |
+==========+==============+
| callerid | TBD |
+----------+--------------+
| uuie | TBD |
+----------+--------------+
| dtmf | TBD |
+----------+--------------+
| external | TBD |
+----------+--------------+
Table 88
15.2.9. Table: Semantics for the "ssrc-group" SDP Attribute
The following values have been added to the "Semantics for the 'ssrc-
group' SDP Attribute" subregistry of the "Session Description
Protocol (SDP) Parameters" registry. The references have been
updated to point to this RFC as well as the previous references.
+========+==============+
| Token | Mux Category |
+========+==============+
| FID | NORMAL |
+--------+--------------+
| FEC | NORMAL |
+--------+--------------+
| FEC-FR | NORMAL |
+--------+--------------+
| DUP | NORMAL |
+--------+--------------+
Table 89
15.2.10. Table: SDP/RTSP Key Management Protocol Identifiers
The following values have been added to the "SDP/RTSP key management
protocol identifiers" subregistry of the "Session Description
Protocol (SDP) Parameters" registry. The references have been
updated to point to this RFC as well as the previous references.
+============+==============+
| Value Name | Mux Category |
+============+==============+
| mikey | IDENTICAL |
+------------+--------------+
Table 90
15.2.11. Table: Codec Control Messages
The following values have been added to the "Codec Control Messages"
subregistry of the "Session Description Protocol (SDP) Parameters"
registry. The references have been updated to point to this RFC as
well as the previous references.
+============+==================+
| Value Name | Mux Category |
+============+==================+
| fir | IDENTICAL-PER-PT |
+------------+------------------+
| tmmbr | IDENTICAL-PER-PT |
+------------+------------------+
| tstr | IDENTICAL-PER-PT |
+------------+------------------+
| vbcm | IDENTICAL-PER-PT |
+------------+------------------+
Table 91
15.2.12. Table: QoS Mechanism Tokens
The following values have been added to the "QoS Mechanism Tokens"
subregistry of the "Session Description Protocol (SDP) Parameters"
registry. The references have been updated to point to this RFC as
well as the previous references.
+===============+==============+
| QoS Mechanism | Mux Category |
+===============+==============+
| rsvp | TRANSPORT |
+---------------+--------------+
| nsis | TRANSPORT |
+---------------+--------------+
Table 92
15.2.13. Table: SDP Capability Negotiation Option Tags
The following values have been added to the "SDP Capability
Negotiation Option Tags" subregistry of the "Session Description
Protocol (SDP) Parameters" registry. The references have been
updated to point to this RFC as well as the previous references.
+============+==============+
| Option Tag | Mux Category |
+============+==============+
| cap-v0 | NORMAL |
+------------+--------------+
| med-v0 | NORMAL |
+------------+--------------+
| bcap-v0 | NORMAL |
+------------+--------------+
| ccap-v0 | NORMAL |
+------------+--------------+
| icap-v0 | NORMAL |
+------------+--------------+
Table 93
15.2.14. Table: Timestamp Reference Clock Source Parameters
The following values have been added to the "Timestamp Reference
Clock Source Parameters" subregistry of the "Session Description
Protocol (SDP) Parameters" registry. The references have been
updated to point to this RFC as well as the previous references.
+=========+==============+
| Name | Mux Category |
+=========+==============+
| ntp | NORMAL |
+---------+--------------+
| ptp | NORMAL |
+---------+--------------+
| gps | NORMAL |
+---------+--------------+
| gal | NORMAL |
+---------+--------------+
| glonass | NORMAL |
+---------+--------------+
| local | NORMAL |
+---------+--------------+
| private | NORMAL |
+---------+--------------+
Table 94
15.2.15. Table: Media Clock Source Parameters
The following values have been added to the "Media Clock Source
Parameters" subregistry of the "Session Description Protocol (SDP)
Parameters" registry. The references have been updated to point to
this RFC as well as the previous references.
+==========+==============+
| Name | Mux Category |
+==========+==============+
| sender | NORMAL |
+----------+--------------+
| direct | NORMAL |
+----------+--------------+
| IEEE1722 | NORMAL |
+----------+--------------+
Table 95
16. Security Considerations
The primary security considerations for RTP, including the way it is
used here, are described in [RFC3550] and [RFC3711].
When multiplexing SDP attributes with the category "CAUTION", the
implementations should be aware of possible issues described in this
specification.
17. References
17.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <https://www.rfc-editor.org/info/rfc4566>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8843] Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", RFC 8843,
DOI 10.17487/RFC8843, January 2021,
<https://www.rfc-editor.org/info/rfc8843>.
17.2. Informative References
[FLUTE] Walsh, R., Peltotalo, J., Peltotalo, S., Curcio, I. D.,
and H. Mehta, "SDP Descriptors for FLUTE", Work in
Progress, Internet-Draft, draft-ietf-rmt-flute-sdp-03, 12
September 2012,
<https://tools.ietf.org/html/draft-ietf-rmt-flute-sdp-03>.
[H.248.15] ITU-T, "Gateway control protocol: SDP ITU-T H.248 package
attribute", ITU-T Recommendation H.248.15, March 2013,
<https://www.itu.int/rec/T-REC-H.248.15>.
[IANA] IANA, "Session Description Protocol (SDP) Parameters",
<https://www.iana.org/assignments/sdp-parameters>.
[IMS-CAT] 3GPP, "IP Multimedia Subsystem (IMS) Customized Alerting
Tones (CAT); Protocol specification",
Specification 24.182, Specification 24.182, January 2015,
<https://www.3gpp.org/ftp/Specs/html-info/24182.htm>.
[IMS-CRS] 3GPP, "IP Multimedia Subsystem (IMS) Customized Ringing
Signal (CRS); Protocol specification",
Specification 24.183, September 2016,
<https://www.3gpp.org/ftp/Specs/html-info/24183.htm>.
[IP-CALL] 3GPP, "IP multimedia call control protocol based on
Session Initiation Protocol (SIP) and Session Description
Protocol (SDP); Stage 3", Specification 24.229, September
2016,
<https://www.3gpp.org/ftp/Specs/html-info/24229.htm>.
[Q.1970] ITU-T, "Q.1970: BICC IP bearer control protocol", ITU-T
Recommendation Q.1970, September 2006,
<https://www.itu.int/rec/T-REC-Q.1970-200609-I/en>.
[RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
Streaming Protocol (RTSP)", RFC 2326,
DOI 10.17487/RFC2326, April 1998,
<https://www.rfc-editor.org/info/rfc2326>.
[RFC3108] Kumar, R. and M. Mostafa, "Conventions for the use of the
Session Description Protocol (SDP) for ATM Bearer
Connections", RFC 3108, DOI 10.17487/RFC3108, May 2001,
<https://www.rfc-editor.org/info/rfc3108>.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002,
<https://www.rfc-editor.org/info/rfc3264>.
[RFC3312] Camarillo, G., Ed., Marshall, W., Ed., and J. Rosenberg,
"Integration of Resource Management and Session Initiation
Protocol (SIP)", RFC 3312, DOI 10.17487/RFC3312, October
2002, <https://www.rfc-editor.org/info/rfc3312>.
[RFC3407] Andreasen, F., "Session Description Protocol (SDP) Simple
Capability Declaration", RFC 3407, DOI 10.17487/RFC3407,
October 2002, <https://www.rfc-editor.org/info/rfc3407>.
[RFC3524] Camarillo, G. and A. Monrad, "Mapping of Media Streams to
Resource Reservation Flows", RFC 3524,
DOI 10.17487/RFC3524, April 2003,
<https://www.rfc-editor.org/info/rfc3524>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <https://www.rfc-editor.org/info/rfc3550>.
[RFC3556] Casner, S., "Session Description Protocol (SDP) Bandwidth
Modifiers for RTP Control Protocol (RTCP) Bandwidth",
RFC 3556, DOI 10.17487/RFC3556, July 2003,
<https://www.rfc-editor.org/info/rfc3556>.
[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute
in Session Description Protocol (SDP)", RFC 3605,
DOI 10.17487/RFC3605, October 2003,
<https://www.rfc-editor.org/info/rfc3605>.
[RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed.,
"RTP Control Protocol Extended Reports (RTCP XR)",
RFC 3611, DOI 10.17487/RFC3611, November 2003,
<https://www.rfc-editor.org/info/rfc3611>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004,
<https://www.rfc-editor.org/info/rfc3711>.
[RFC3890] Westerlund, M., "A Transport Independent Bandwidth
Modifier for the Session Description Protocol (SDP)",
RFC 3890, DOI 10.17487/RFC3890, September 2004,
<https://www.rfc-editor.org/info/rfc3890>.
[RFC4091] Camarillo, G. and J. Rosenberg, "The Alternative Network
Address Types (ANAT) Semantics for the Session Description
Protocol (SDP) Grouping Framework", RFC 4091,
DOI 10.17487/RFC4091, June 2005,
<https://www.rfc-editor.org/info/rfc4091>.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145,
DOI 10.17487/RFC4145, September 2005,
<https://www.rfc-editor.org/info/rfc4145>.
[RFC4567] Arkko, J., Lindholm, F., Naslund, M., Norrman, K., and E.
Carrara, "Key Management Extensions for Session
Description Protocol (SDP) and Real Time Streaming
Protocol (RTSP)", RFC 4567, DOI 10.17487/RFC4567, July
2006, <https://www.rfc-editor.org/info/rfc4567>.
[RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session
Description Protocol (SDP) Security Descriptions for Media
Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006,
<https://www.rfc-editor.org/info/rfc4568>.
[RFC4570] Quinn, B. and R. Finlayson, "Session Description Protocol
(SDP) Source Filters", RFC 4570, DOI 10.17487/RFC4570,
July 2006, <https://www.rfc-editor.org/info/rfc4570>.
[RFC4572] Lennox, J., "Connection-Oriented Media Transport over the
Transport Layer Security (TLS) Protocol in the Session
Description Protocol (SDP)", RFC 4572,
DOI 10.17487/RFC4572, July 2006,
<https://www.rfc-editor.org/info/rfc4572>.
[RFC4574] Levin, O. and G. Camarillo, "The Session Description
Protocol (SDP) Label Attribute", RFC 4574,
DOI 10.17487/RFC4574, August 2006,
<https://www.rfc-editor.org/info/rfc4574>.
[RFC4583] Camarillo, G., "Session Description Protocol (SDP) Format
for Binary Floor Control Protocol (BFCP) Streams",
RFC 4583, DOI 10.17487/RFC4583, November 2006,
<https://www.rfc-editor.org/info/rfc4583>.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
DOI 10.17487/RFC4585, July 2006,
<https://www.rfc-editor.org/info/rfc4585>.
[RFC4796] Hautakorpi, J. and G. Camarillo, "The Session Description
Protocol (SDP) Content Attribute", RFC 4796,
DOI 10.17487/RFC4796, February 2007,
<https://www.rfc-editor.org/info/rfc4796>.
[RFC4975] Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed.,
"The Message Session Relay Protocol (MSRP)", RFC 4975,
DOI 10.17487/RFC4975, September 2007,
<https://www.rfc-editor.org/info/rfc4975>.
[RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
"Codec Control Messages in the RTP Audio-Visual Profile
with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104,
February 2008, <https://www.rfc-editor.org/info/rfc5104>.
[RFC5109] Li, A., Ed., "RTP Payload Format for Generic Forward Error
Correction", RFC 5109, DOI 10.17487/RFC5109, December
2007, <https://www.rfc-editor.org/info/rfc5109>.
[RFC5159] Dondeti, L., Ed. and A. Jerichow, "Session Description
Protocol (SDP) Attributes for Open Mobile Alliance (OMA)
Broadcast (BCAST) Service and Content Protection",
RFC 5159, DOI 10.17487/RFC5159, March 2008,
<https://www.rfc-editor.org/info/rfc5159>.
[RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP
Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July
2008, <https://www.rfc-editor.org/info/rfc5285>.
[RFC5432] Polk, J., Dhesikan, S., and G. Camarillo, "Quality of
Service (QoS) Mechanism Selection in the Session
Description Protocol (SDP)", RFC 5432,
DOI 10.17487/RFC5432, March 2009,
<https://www.rfc-editor.org/info/rfc5432>.
[RFC5506] Johansson, I. and M. Westerlund, "Support for Reduced-Size
Real-Time Transport Control Protocol (RTCP): Opportunities
and Consequences", RFC 5506, DOI 10.17487/RFC5506, April
2009, <https://www.rfc-editor.org/info/rfc5506>.
[RFC5547] Garcia-Martin, M., Isomaki, M., Camarillo, G., Loreto, S.,
and P. Kyzivat, "A Session Description Protocol (SDP)
Offer/Answer Mechanism to Enable File Transfer", RFC 5547,
DOI 10.17487/RFC5547, May 2009,
<https://www.rfc-editor.org/info/rfc5547>.
[RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific
Media Attributes in the Session Description Protocol
(SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009,
<https://www.rfc-editor.org/info/rfc5576>.
[RFC5583] Schierl, T. and S. Wenger, "Signaling Media Decoding
Dependency in the Session Description Protocol (SDP)",
RFC 5583, DOI 10.17487/RFC5583, July 2009,
<https://www.rfc-editor.org/info/rfc5583>.
[RFC5760] Ott, J., Chesterfield, J., and E. Schooler, "RTP Control
Protocol (RTCP) Extensions for Single-Source Multicast
Sessions with Unicast Feedback", RFC 5760,
DOI 10.17487/RFC5760, February 2010,
<https://www.rfc-editor.org/info/rfc5760>.
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
Control Packets on a Single Port", RFC 5761,
DOI 10.17487/RFC5761, April 2010,
<https://www.rfc-editor.org/info/rfc5761>.
[RFC5762] Perkins, C., "RTP and the Datagram Congestion Control
Protocol (DCCP)", RFC 5762, DOI 10.17487/RFC5762, April
2010, <https://www.rfc-editor.org/info/rfc5762>.
[RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework
for Establishing a Secure Real-time Transport Protocol
(SRTP) Security Context Using Datagram Transport Layer
Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May
2010, <https://www.rfc-editor.org/info/rfc5763>.
[RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description
Protocol (SDP) Grouping Framework", RFC 5888,
DOI 10.17487/RFC5888, June 2010,
<https://www.rfc-editor.org/info/rfc5888>.
[RFC5939] Andreasen, F., "Session Description Protocol (SDP)
Capability Negotiation", RFC 5939, DOI 10.17487/RFC5939,
September 2010, <https://www.rfc-editor.org/info/rfc5939>.
[RFC5956] Begen, A., "Forward Error Correction Grouping Semantics in
the Session Description Protocol", RFC 5956,
DOI 10.17487/RFC5956, September 2010,
<https://www.rfc-editor.org/info/rfc5956>.
[RFC6064] Westerlund, M. and P. Frojdh, "SDP and RTSP Extensions
Defined for 3GPP Packet-Switched Streaming Service and
Multimedia Broadcast/Multicast Service", RFC 6064,
DOI 10.17487/RFC6064, January 2011,
<https://www.rfc-editor.org/info/rfc6064>.
[RFC6128] Begen, A., "RTP Control Protocol (RTCP) Port for Source-
Specific Multicast (SSM) Sessions", RFC 6128,
DOI 10.17487/RFC6128, February 2011,
<https://www.rfc-editor.org/info/rfc6128>.
[RFC6189] Zimmermann, P., Johnston, A., Ed., and J. Callas, "ZRTP:
Media Path Key Agreement for Unicast Secure RTP",
RFC 6189, DOI 10.17487/RFC6189, April 2011,
<https://www.rfc-editor.org/info/rfc6189>.
[RFC6193] Saito, M., Wing, D., and M. Toyama, "Media Description for
the Internet Key Exchange Protocol (IKE) in the Session
Description Protocol (SDP)", RFC 6193,
DOI 10.17487/RFC6193, April 2011,
<https://www.rfc-editor.org/info/rfc6193>.
[RFC6230] Boulton, C., Melanchuk, T., and S. McGlashan, "Media
Control Channel Framework", RFC 6230,
DOI 10.17487/RFC6230, May 2011,
<https://www.rfc-editor.org/info/rfc6230>.
[RFC6236] Johansson, I. and K. Jung, "Negotiation of Generic Image
Attributes in the Session Description Protocol (SDP)",
RFC 6236, DOI 10.17487/RFC6236, May 2011,
<https://www.rfc-editor.org/info/rfc6236>.
[RFC6284] Begen, A., Wing, D., and T. Van Caenegem, "Port Mapping
between Unicast and Multicast RTP Sessions", RFC 6284,
DOI 10.17487/RFC6284, June 2011,
<https://www.rfc-editor.org/info/rfc6284>.
[RFC6285] Ver Steeg, B., Begen, A., Van Caenegem, T., and Z. Vax,
"Unicast-Based Rapid Acquisition of Multicast RTP
Sessions", RFC 6285, DOI 10.17487/RFC6285, June 2011,
<https://www.rfc-editor.org/info/rfc6285>.
[RFC6364] Begen, A., "Session Description Protocol Elements for the
Forward Error Correction (FEC) Framework", RFC 6364,
DOI 10.17487/RFC6364, October 2011,
<https://www.rfc-editor.org/info/rfc6364>.
[RFC6642] Wu, Q., Ed., Xia, F., and R. Even, "RTP Control Protocol
(RTCP) Extension for a Third-Party Loss Report", RFC 6642,
DOI 10.17487/RFC6642, June 2012,
<https://www.rfc-editor.org/info/rfc6642>.
[RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.,
and K. Carlberg, "Explicit Congestion Notification (ECN)
for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August
2012, <https://www.rfc-editor.org/info/rfc6679>.
[RFC6714] Holmberg, C., Blau, S., and E. Burger, "Connection
Establishment for Media Anchoring (CEMA) for the Message
Session Relay Protocol (MSRP)", RFC 6714,
DOI 10.17487/RFC6714, August 2012,
<https://www.rfc-editor.org/info/rfc6714>.
[RFC6773] Phelan, T., Fairhurst, G., and C. Perkins, "DCCP-UDP: A
Datagram Congestion Control Protocol UDP Encapsulation for
NAT Traversal", RFC 6773, DOI 10.17487/RFC6773, November
2012, <https://www.rfc-editor.org/info/rfc6773>.
[RFC6787] Burnett, D. and S. Shanmugham, "Media Resource Control
Protocol Version 2 (MRCPv2)", RFC 6787,
DOI 10.17487/RFC6787, November 2012,
<https://www.rfc-editor.org/info/rfc6787>.
[RFC6849] Kaplan, H., Ed., Hedayat, K., Venna, N., Jones, P., and N.
Stratton, "An Extension to the Session Description
Protocol (SDP) and Real-time Transport Protocol (RTP) for
Media Loopback", RFC 6849, DOI 10.17487/RFC6849, February
2013, <https://www.rfc-editor.org/info/rfc6849>.
[RFC6871] Gilman, R., Even, R., and F. Andreasen, "Session
Description Protocol (SDP) Media Capabilities
Negotiation", RFC 6871, DOI 10.17487/RFC6871, February
2013, <https://www.rfc-editor.org/info/rfc6871>.
[RFC6947] Boucadair, M., Kaplan, H., Gilman, R., and S.
Veikkolainen, "The Session Description Protocol (SDP)
Alternate Connectivity (ALTC) Attribute", RFC 6947,
DOI 10.17487/RFC6947, May 2013,
<https://www.rfc-editor.org/info/rfc6947>.
[RFC7006] Garcia-Martin, M., Veikkolainen, S., and R. Gilman,
"Miscellaneous Capabilities Negotiation in the Session
Description Protocol (SDP)", RFC 7006,
DOI 10.17487/RFC7006, September 2013,
<https://www.rfc-editor.org/info/rfc7006>.
[RFC7104] Begen, A., Cai, Y., and H. Ou, "Duplication Grouping
Semantics in the Session Description Protocol", RFC 7104,
DOI 10.17487/RFC7104, January 2014,
<https://www.rfc-editor.org/info/rfc7104>.
[RFC7195] Garcia-Martin, M. and S. Veikkolainen, "Session
Description Protocol (SDP) Extension for Setting Audio and
Video Media Streams over Circuit-Switched Bearers in the
Public Switched Telephone Network (PSTN)", RFC 7195,
DOI 10.17487/RFC7195, May 2014,
<https://www.rfc-editor.org/info/rfc7195>.
[RFC7197] Begen, A., Cai, Y., and H. Ou, "Duplication Delay
Attribute in the Session Description Protocol", RFC 7197,
DOI 10.17487/RFC7197, April 2014,
<https://www.rfc-editor.org/info/rfc7197>.
[RFC7266] Clark, A., Wu, Q., Schott, R., and G. Zorn, "RTP Control
Protocol (RTCP) Extended Report (XR) Blocks for Mean
Opinion Score (MOS) Metric Reporting", RFC 7266,
DOI 10.17487/RFC7266, June 2014,
<https://www.rfc-editor.org/info/rfc7266>.
[RFC7272] van Brandenburg, R., Stokking, H., van Deventer, O.,
Boronat, F., Montagud, M., and K. Gross, "Inter-
Destination Media Synchronization (IDMS) Using the RTP
Control Protocol (RTCP)", RFC 7272, DOI 10.17487/RFC7272,
June 2014, <https://www.rfc-editor.org/info/rfc7272>.
[RFC7273] Williams, A., Gross, K., van Brandenburg, R., and H.
Stokking, "RTP Clock Source Signalling", RFC 7273,
DOI 10.17487/RFC7273, June 2014,
<https://www.rfc-editor.org/info/rfc7273>.
[RFC7657] Black, D., Ed. and P. Jones, "Differentiated Services
(Diffserv) and Real-Time Communication", RFC 7657,
DOI 10.17487/RFC7657, November 2015,
<https://www.rfc-editor.org/info/rfc7657>.
[RFC7826] Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M.,
and M. Stiemerling, Ed., "Real-Time Streaming Protocol
Version 2.0", RFC 7826, DOI 10.17487/RFC7826, December
2016, <https://www.rfc-editor.org/info/rfc7826>.
[RFC8122] Lennox, J. and C. Holmberg, "Connection-Oriented Media
Transport over the Transport Layer Security (TLS) Protocol
in the Session Description Protocol (SDP)", RFC 8122,
DOI 10.17487/RFC8122, March 2017,
<https://www.rfc-editor.org/info/rfc8122>.
[RFC8285] Singer, D., Desineni, H., and R. Even, Ed., "A General
Mechanism for RTP Header Extensions", RFC 8285,
DOI 10.17487/RFC8285, October 2017,
<https://www.rfc-editor.org/info/rfc8285>.
[RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445,
DOI 10.17487/RFC8445, July 2018,
<https://www.rfc-editor.org/info/rfc8445>.
[RFC8856] Camarillo, G., Kristensen, T., and C. Holmberg, "Session
Description Protocol (SDP) Format for Binary Floor Control
Protocol (BFCP) Streams", RFC 8856, DOI 10.17487/RFC8856,
January 2021, <https://www.rfc-editor.org/info/rfc8856>.
[RFC8866] Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
Session Description Protocol", RFC 8866,
DOI 10.17487/RFC8866, January 2021,
<https://www.rfc-editor.org/info/rfc8866>.
[T.38] ITU-T, "Procedures for real-time Group 3 facsimile
communication over IP networks", ITU-T
Recommendation T.38, November 2015,
<https://www.itu.int/rec/T-REC-T.38/e>.
[TISPAN] ETSI, "Telecommunications and Internet converged Services
and Protocols for Advanced Networking (TISPAN); IMS-based
IPTV stage 3 specification", Technical Specification 183
063 V2.1.0, June 2008, <https://www.etsi.org/deliver/
etsi_ts/183000_183099/183063/02.01.00_60/
ts_183063v020100p.pdf>.
Acknowledgements
I would like to thank Cullen Jennings and Flemming Andreasen for
suggesting the categories, contributing text, and reviewing the draft
of this document. I would also like to thank Magnus Westerlund,
Christer Holmberg, Jonathan Lennox, Bo Burman, Ari Keränen, and Dan
Wing for suggesting structural changes that improved the document's
readability.
I would like also to thank the following experts for their inputs and
reviews as listed:
Flemming Andreasen (5.24, 5.32, 5.33, 14),
Rohan Mahy (5.54),
Eric Burger (5.26),
Christian Huitema (5.14),
Christer Holmberg (5.21, 5.26, 12.2, 12.3),
Richard Ejzak (5.44, 5.50, 5.51),
Colin Perkins (5.7, 5.8, 5.9, 5.55),
Magnus Westerlund (5.2, 5.3, 5.9, 5.27, 5.47, 6.1 - 6.3, 8.3, 7),
Roni Even (5.12, 5.27, 8.4),
Subha Dhesikan (5.6, 10),
Dan Wing (5.7, 5.12, 5.35, 5.39, 5.45),
Cullen Jennings (5.40),
Ali C Begen (5.1, 5.20, 5.22, 5.25, 5.38, 7.3, 8.2, 8.4, 8.6, 9.2,
13.1),
Bo Burman (7.2, 7.6),
Charles Eckel (5.15, 5.27, 5.28, 9.1, 8.5),
Paul Kyzivat (5.24),
Ian Johansson (5.15),
Saravanan Shanmugham (5.11),
Paul E Jones (5.30),
Rajesh Kumar (5.48),
Jonathan Lennox (5.36, 5, 15, 9.1, 11.1),
Mo Zanaty (5.4, 5.5, 5.23, 8.1, 8.3, 8.5, 12.1),
Christian Huitema (5.14),
Qin Wu (5.47, PM-Dir review),
Hans Stokking (5.43, 5.16),
Christian Groves (5.48, 5.52), and
Thomas Stach.
I would like to thank Chris Lonvick for the SECDIR review, Dan
Romascanu for the Gen-ART review, and Sabrina Tanamal for the IANA
review.
Thanks to Ben Campbell for Area Director review suggestions. Thanks
to Spencer Dawkins, Stephen Farrel, Alissa Cooper, Mirja Kühlewind,
and the entire IESG for their reviews.
Author's Address
Suhas Nandakumar
Cisco
170 West Tasman Drive
San Jose, CA 95134
United States of America
Email: snandaku@cisco.com
