Network Working Group S. Nandakumar
Internet-Draft Cisco
Intended status: Standards Track September 22, 2016
Expires: March 26, 2017

A Framework for SDP Attributes when Multiplexing
draft-ietf-mmusic-sdp-mux-attributes-14

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 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 Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on March 26, 2017.

Copyright Notice

Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.


Table of Contents

1. Introduction

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 [I-D.ietf-mmusic-sdp-bundle-negotiation] 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) [RFC5245] 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 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/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 http://www.3gpp.org for more information about this organization.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

3. Motivation

The time and complications of setting up ICE [RFC5245] and Datagram Transport Layer Security (DTLS) based Secure Real-time Transport Protocol (SRTP) [RFC5763] transports for use by RTP, reasons to conserve ports bindings on the Network Address Translators (NAT), forms a requirement to try and reduce the number of transport level flows needed. This has resulted in the definition of ways, such as [I-D.ietf-mmusic-sdp-bundle-negotiation] 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 which 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 or media-level or source-level. Informally, there are various semantic groupings for these attributes. One such grouping could be notes as below:

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

The attributes in the CAUTION category are advised against multiplexing 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 being a connection oriented protocol 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
           

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, "a=crypto" attribute is defined for both the audio and the 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 BUNDLE grouping semantic [I-D.ietf-mmusic-sdp-bundle-negotiation] which mandates the values from "m=" line corresponding to the mid appearing first on the a=group:BUNDLE line to 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 transport, media, and media format related capabilities in the SDP.

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 the above 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 per Payload Type basis and 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 the Section 10.1.2 of [I-D.ietf-mmusic-sdp-bundle-negotiation] 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 (ex: rtpmap, fmtp) are identical (Note: some line breaks included 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 exampe, for the attribute extmap [RFC5285], the specification defining the extension needs to be referred 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:

The "Mux Category" column identifies multiplexing category assigned per attribute and the "Notes" column captures additional informative details regarding the assigned category, wherever necessary.

5.1. RFC4566: 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.

5.1 RFC4566 Attribute Analysis
Name Notes Level Mux Category
sendrecv  Not impacted  NORMAL 
sendonly  Not impacted  NORMAL 
recvonly  Not impacted  NORMAL 
inactive  Not impacted  NORMAL 
cat  Not impacted  NORMAL 
ptime  The attribute value MUST be same for a given codec configuration  IDENTICAL-PER-PT
maxptime  The attribute value MUST be same for a given codec configuration  IDENTICAL-PER-PT
orient  Not Impacted   NORMAL
framerate  The attribute value MUST be same for a given codec configuration  IDENTICAL-PER-PT 
quality  Not Impacted   NORMAL
rtpmap  The attribute value MUST be same for a given codec configuration  IDENTICAL-PER-PT
fmtp  The attribute value MUST be same for a given codec configuration  IDENTICAL-PER-PT
keywds  Not impacted  NORMAL 
type  Not Impacted   NORMAL 
type:broadcast  Not Impacted   NORMAL 
type:H332  Not Impacted   NORMAL 
type:meeting  Not Impacted   NORMAL 
type:moderated  Not Impacted   NORMAL 
type:test  Not Impacted   NORMAL 
tool  Not Impacted   NORMAL 
charset  Not Impacted   NORMAL 
sdplang  Not Impacted   NORMAL 
lang  Not Impacted   NORMAL 

5.2. RFC4585: 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.

5.2 RFC4585 Attribute Analysis
Name Notes Level Mux Category
rtcp-fb  Since RTCP feedback attributes are Payload Type (PT) scoped, their values MUST be identical for a given PT across the multiplexed "m=" lines. M IDENTICAL-PER-PT 

5.3. RFC5761: 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.

5.3 RFC5761 Attribute Analysis
Name Notes Level Mux Category
rtcp-mux  RTP and RTCP Multiplexing affects the entire RTP session  IDENTICAL 

5.4. RFC3312: 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.

5.4 RFC3312 Attribute Analysis
Name Notes Level Mux Category
des  Refer to notes below  CAUTION 
conf  Refer to notes below  CAUTION 
curr  Refer to notes below  CAUTION 

NOTE: A mismatched set of preconditions across media descriptions results in Session establishment failures due to inability to meet right resource reservations requested.

5.5. RFC4574: 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.

5.5 RFC4574 Attribute Analysis
Name Notes Level Mux Category
label  Not Impacted  M NORMAL 

5.6. RFC5432: QOS Mechanism Selection in SDP

[RFC5432] defines procedures to negotiate QOS mechanisms using the SDP offer/answer model.

5.6 RFC5432 Attribute Analysis
Name Notes Level Mux Category
qos-mech-send  Refer to Section 10   B TRANSPORT 
qos-mech-recv  Refer to Section 10   B TRANSPORT 

5.7. RFC4568: SDP Security Descriptions

[RFC4568] defines a 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.

5.7 RFC4568 Attribute Analysis
Name Notes Level Mux Category
crypto  crypto attribute MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow TRANSPORT 

5.8. RFC5762: 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.

5.8 RFC5762 Attribute Analysis
Name Notes Current Mux Category
dccp-service-code  If RFC6773 is not being used in addition to RFC5762, the port in the "m=" line is a DCCP port. DCCP being a connection oriented protocol does not allow multiple connections on the same 5-tuple  CAUTION 

NOTE: If RFC6773 is being used in addition to RFC5762 and provided that DCCP-in-UDP layer has additional demultiplexing, then it can be possible to use different DCCP service codes for each DCCP flow, given each uses a different DCCP port. Although 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. RFC6773: 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) middle boxes without modification of those middle boxes.

5.9 RFC6773 Attribute Analysis
Name Notes Level Mux Category
dccp-port  Multiplexing is not recommended due to potential conflict between the port used for DCCP en/decapsulation and the RTP  CAUTION 

NOTE: RFC6773 is about tunneling DCCP in UDP, with the UDP port being the port of the DCCP en-/de-capsulation 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. For 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. This can or cannot work depending on the nature of DCCP encapsulation and ports choices thus rendering it to be very application dependent.

5.10. RFC5506: Reduced-Size RTCP in RTP Profile

[RFC5506] discusses benefits and issues that arise when allowing RTCP packets to be transmitted with reduced size.

5.10 RFC5506 Attribute Analysis
Name Notes Level Mux Category
rtcp-rsize  Reduced size RTCP affects the entire RTP session  IDENTICAL 

5.11. RFC6787: 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.

5.11 RFC6787 Attribute Analysis
Name Notes Level Mux Category
resource  Not Impacted  NORMAL 
channel  Not Impacted  NORMAL 
cmid  Not Impacted  NORMAL 

5.12. RFC5245: ICE

[RFC5245] 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.

5.12 RFC5245 Attribute Analysis
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 that corresponds to the "m=" line chosen for setting up the underlying transport flow  B TRANSPORT 
ice-ufrag  ice-ufrag MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow  B TRANSPORT 
candidate  ice candidate MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow  M TRANSPORT 
remote-candidates  ice remote candidate MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow  M TRANSPORT 

5.13. RFC5285: RTP Header Extensions

[RFC5285] provides a general mechanism to use the header extension feature of RTP. 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 de-centralized. The actual extensions in use in a session are signaled in the setup information for that session.

5.13 RFC5285 Attribute Analysis
Name Notes Level Mux Category
extmap  Refer to the document defining the specific RTP Extension  B SPECIAL 

5.14. RFC3605: 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 to indicate the RTCP port.

5.14 RFC3605 Attribute Analysis
Name Notes Level Mux Category
rtcp  RTCP Port MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow.  M TRANSPORT 

5.15. RFC5576: Source-Specific SDP Attributes

[RFC5576] defines a mechanism to describe RTP media sources, which are identified by their synchronization source (SSRC) identifiers, in SDP, to associate attributes with these sources, and to express relationships among sources. It also defines several source-level attributes that can be used to describe properties of media sources.

5.15 RFC5576 Attribute Analysis
Name Notes Level Mux Category
ssrc  Refer to Notes below  M NORMAL 
ssrc-group  Refer to Section 9 for specific analysis of the grouping semantics  M NORMAL 
cname  Not Impacted  SR NORMAL 
previous-ssrc  Refer to notes below  SR NORMAL 
fmtp  The attribute value MUST be same for a given codec configuration  SR IDENTICAL-PER-PT 

NOTE: If SSRCs are repeated across "m=" lines being multiplexed, they MUST all represent the same underlying RTP Source.

5.16. RFC7273: RTP Clock Source Signalling

[RFC7273] specifies SDP signalling that identifies timestamp reference clock sources and SDP signalling that identifies the media clock sources in a multimedia session.

5.16 RFC7273 Attribute Analysis
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 

5.17. RFC6236: 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 hand-held 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.

5.17 RFC6236 Attribute Analysis
Name Notes Level Mux Category
imageattr  The attribute value MUST be same for a given codec configuration  IDENTICAL-PER-PT 

5.18. RFC7197: Duplication Delay Attribute in SDP

[RFC7197] defines an attribute to indicate the presence of temporally redundant media streams and the duplication delay in SDP.

5.18 RFC7197 Attribute Analysis
Name Notes Level Mux Category
duplication-delay  Not Impacted  NORMAL 

5.19. RFC7266: RTCP XR Blocks for MOS Metric Reporting

[RFC7266] defines an RTCP Extended Report (XR) Block including 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.

5.19 RFC7266 Attribute Analysis
Name Notes Level Mux Category
calgextmap  Not Impacted  NORMAL 

5.20. RFC6285: Rapid Acquisition of Multicast RTP Sessions

[RFC6285] describes a method 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.

5.20 RFC6285 Attribute Analysis
Name Notes Level Mux Category
rams-updates  Not recommended   CAUTION 

5.21. RFC6230: 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.

5.21 RFC6230 Attribute Analysis
Name Notes Level Mux Category
cfw-id  Not Impacted  NORMAL 

5.22. RFC6364: 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.

5.22 RFC6364 Attribute Analysis
Name Notes Level Mux Category
fec-source-flow  Refer to the document defining specific FEC Scheme  SPECIAL 
fec-repair-flow  Refer to the document defining specific FEC Scheme  SPECIAL 
repair-window  Refer to the document defining specific FEC Scheme  SPECIAL 

5.23. RFC4796: 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.

5.23 RFC4796 Attribute Analysis
Name Notes Level Mux Category
content  Not Impacted  NORMAL 

5.24. RFC3407: SDP Simple Capability Declaration

[RFC3407] defines a set of SDP attributes that enables SDP to provide a minimal and backwards compatible capability declaration mechanism.

5.24 RFC3407 Attribute Analysis
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 

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 actual attribute being encapsulated and the implications of the numerical values assigned. Hence it is recommended to consult the specification defining attributes (cparmin/cparmax) to further analyze their behavior under multiplexing.

5.25. RFC6284: 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.

5.25 RFC6284 Attribute Analysis
Name Notes Level Mux Category
portmapping-req  Not recommended, if port mapping is required by the application  CAUTION 

5.26. RFC6714: 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 middle boxes to anchor the MSRP connection, without the need for middle boxes to modify the MSRP messages; thus, it also enables secure end-to-end MSRP communication in networks where such middle boxes are deployed. This document also defines a SDP attribute, 'msrp-cema', that MSRP endpoints use to indicate support of the CEMA extension.

5.26 RFC6714 Attribute Analysis
Name Notes Level Mux Category
msrp-cema  Refer to notes below  TBD 

NOTE: As per section 9.1 of [I-D.ietf-mmusic-sdp-bundle-negotiation], there exists no publicly available specification that defines procedures for multiplexing/demultiplexing MRSP 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.

5.27. RFC4583: SDP Format for BFCP Streams

[RFC4583] document 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.

5.27 RFC4583 Attribute Analysis
Name Notes Level Mux Category
floorctrl  The attribute MUST be repeated across all the multiplexed "m=" lines  IDENTICAL 
confid  Not Impacted  NORMAL 
userid  Not Impacted  NORMAL 
floorid  Not Impacted  NORMAL 

5.28. RFC5547: 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].

5.28 RFC5547 Attribute Analysis
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 

NOTE: As per section 9.1 of [I-D.ietf-mmusic-sdp-bundle-negotiation], there exists no publicly available specification that defines procedures for multiplexing/demultiplexing MRSP flows over a single 5-tuple. Once such a specification is available, the multiplexing categories assignments for attributes in this section could be revisited.

5.29. RFC6849: SDP and RTP Media Loopback Extension

[RFC6849] adds new SDP media types and attributes, which 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.

5.29 RFC6849 Analysis
Name Notes Level Mux Category
loopback rtp-pkt-loopback  The attribute value MUST be same for a given codec configuration  M IDENTICAL-PER-PT 
loopback rtp-media-loopback  The attribute value MUST be same for a given codec configuration   M IDENTICAL-PER-PT 
loopback-source  Not Impacted  M NORMAL 
loopback-mirror  Not Impacted  M NORMAL 

5.30. RFC5760: 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.

5.30 RFC5760 Attribute Analysis
Name Notes Level Mux Category
rtcp-unicast  The attribute MUST be reported across all "m=" lines multiplexed  M IDENTICAL 

5.31. RFC3611: 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).

5.31 RFC3611 Attribute Analysis
Name Notes Level Mux Category
rtcp-xr  Not Impacted  B NORMAL 

5.32. RFC5939: 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.

5.32 RFC5939 Attribute Analysis
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 

5.33. RFC6871: SDP Media Capabilities Negotiation

SDP capability negotiation provides a general framework for indicating and negotiating capabilities in SDP. The base framework defines only 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.

5.33 RFC6871 - Attribute Analysis
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 

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. RFC7006: Miscellaneous Capabilities Negotiation 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).

5.34 RFC7006 - Attribute Analysis
Name Notes Level Mux Category
bcap  Inherit the category SUM as applicable to b= attribute  B INHERIT 
bcap-v0  Not Impacted  B NORMAL 
ccap  The connection address type MUST be identical across all the multiplexed "m=" lines  B IDENTICAL 
ccap-v0  Not Impacted  B NORMAL 
icap  Not Impacted  B NORMAL 
icap-v0  Not Impacted  B NORMAL 

5.35. RFC4567: 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.

5.35 RFC4567 Attribute Analysis
Name Notes Level Mux Category
key-mgmt  Key management protocol MUST be identical across all the "m=" lines  B IDENTICAL 
mikey  Key management protocol MUST be identical across all the "m=" lines  B IDENTICAL 

5.36. RFC4572: 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. 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.

5.36 RFC4572 Attribute Analysis
Name Notes Level Mux Category
fingerprint  fingerprint value from the "m=" line defining the underlying transport is chosen  B TRANSPORT 

5.37. RFC4570: 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.

5.37 RFC4570 Attribute Analysis
Name Notes Level Mux Category
source-filter  The attribute MUST be repeated across all "m=" lines multiplexed  B IDENTICAL 

5.38. RFC6128: 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.

5.38 RFC6128 Attribute Analysis
Name Notes Level Mux Category
multicast-rtcp  Multicast RTCP port MUST be identical across all the "m=" lines  B IDENTICAL 

5.39. RFC6189: 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.

5.39 RFC6189 Attribute Analysis
Name Notes Level Mux Category
zrtp-hash  zrtp-hash attribute MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow  M TRANSPORT 

5.40. RFC4145: 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 reestablishment.

5.40 RFC4145 Attribute Analysis
Name Notes Level Mux Category
setup  The setup attribute MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow.  B TRANSPORT 
connection  The connection attribute MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow.  B TRANSPORT 

5.41. RFC6947: 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 attribute, the "altc" attribute, solves the backward-compatibility problem that plagued Alternative Network Address Types (ANAT) due to their syntax.

5.41 RFC6947 Attribute Analysis
Name Notes Level Mux Category
altc  The IP Address and port MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow  M TRANSPORT 

5.42. RFC7195: SDP Extension for Circuit Switched Bearers in PSTN

[RFC7195] describes use cases, requirements, and protocol extensions for using SDP offer/answer model for establishing audio and video media streams over circuit-switched bearers in the Public Switched Telephone Network (PSTN).

5.42 RFC7195 Attribute Analysis
Name Notes Level Mux Category
cs-correlation:callerid  Refer to notes below  M TBD 
cs-correlation:uuie  Refer to notes below  TBD 
cs-correlation:dtmf  Refer to notes below  M TBD 
cs-correlation:external  Refer to notes below  M TBD 

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 [I-D.ietf-mmusic-sdp-bundle-negotiation] requires the "c=" line nettype value of "IN". If in future there exists 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. RFC7272: 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).

5.43 RFC7272 Attribute Analysis
Name Notes Level Mux Category
rtcp-idms  Not Impacted  M NORMAL 

5.44. RFC5159: Open Mobile Alliance (OMA) Broadcast (BCAST) SDP Attributes

[RFC5159] provides descriptions of SDP attributes used by the Open Mobile Alliance's Broadcast Service and Content Protection specification.

5.44 RFC5159 Attribute Analysis
Name Notes Level Mux Category
bcastversion  Not Impacted  S NORMAL 
stkmstream  Not Impacted  B NORMAL 
SRTPAuthentication  Needs further analysis  M TBD 
SRTPROCTxRate  Needs further analysis  M TBD 

5.45. RFC6193: 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.

5.45 RFC6193 Attribute Analysis
Name Notes Level Mux Category
ike-setup  Unlikely to use IKE in the context of multiplexing  B CAUTION 
psk-fingerprint  Unlikely to use IKE in the context of multiplexing  B CAUTION 
ike-esp  Unlikely to use IKE in the context of multiplexing  B CAUTION 
ike-esp-udpencap  Unlikely to use IKE in the context of multiplexing  B CAUTION 

5.46. RFC2326: 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.

5.46 RFC2326 Attribute Analysis
Name Notes Level Mux Category
etag  RTSP is not supported for RTP Stream multiplexing  B CAUTION 
range  RTSP is not supported for RTP Stream multiplexing  B CAUTION 
control  RTSP is not supported for RTP Stream multiplexing  B CAUTION 
mtag  RTSP is not supported for RTP Stream multiplexing  B CAUTION 

NOTE: [RFC2326] defines SDP attributes that are applicable in the declarative usage of SDP alone. For purposes of this document, only the Offer/Answer usage of SDP is considered as mandated by [I-D.ietf-mmusic-sdp-bundle-negotiation].

5.47. RFC6064: 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.

5.47 RFC6064 Attribute Analysis
Name Notes Level Mux Category
X-predecbufsize  Refer to notes below  M CAUTION 
X-initpredecbufperiod  Refer to notes below  M CAUTION 
X-initpostdecbufperiod  Refer to notes below  M CAUTION 
X-decbyterate Refer to notes below  M CAUTION 
3gpp-videopostdecbufsize  Refer to notes below  M CAUTION 
framesize Refer to notes below  M CAUTION 
3GPP-Integrity-Key  Refer to notes below  S CAUTION 
3GPP-SDP-Auth  Refer to notes below  S CAUTION 
3GPP-SRTP-Config  Refer to notes below   M CAUTION 
alt  Refer to notes below  M CAUTION 
alt-default-id  Refer to notes below  M CAUTION 
alt-group  Refer to notes below  S CAUTION 
3GPP-Adaptation-Support  Refer to notes below   M CAUTION 
3GPP-Asset-Information  Refer to notes below  B CAUTION 
mbms-mode  Refer to notes below  B CAUTION 
mbms-flowid  Refer to notes below  M CAUTION 
mbms-repair  Refer to notes below  B CAUTION 
3GPP-QoE-Metrics  Refer to notes below  M CAUTION 
3GPP-QoE-Metrics:Corruption duration  Refer to notes below  M CAUTION 
3GPP-QoE-Metrics:Rebuffering duration  Refer to notes below  M CAUTION 
3GPP-QoE-Metrics:Initial buffering duration  Refer to notes below  M CAUTION 
3GPP-QoE-Metrics:Successive loss of RTP packets  Refer to notes below  M CAUTION 
3GPP-QoE-Metrics:Frame rate deviation  Refer to notes below  M CAUTION 
3GPP-QoE-Metrics:Jitter duration  Refer to notes below  M CAUTION 
3GPP-QoE-Metrics:Content Switch Time  Refer to notes below  B CAUTION 
3GPP-QoE-Metrics:Average Codec Bitrate  Refer to notes below  M CAUTION 
3GPP-QoE-Metrics:Codec Information  Refer to notes below  M CAUTION 
3GPP-QoE-Metrics:Buffer Status  Refer to notes below  M CAUTION 

NOTE: [RFC6064] defines SDP attributes that are applicable in the declarative usage of SDP alone. For purposes of this document, only the Offer/Answer usage of SDP is considered as mandated by [I-D.ietf-mmusic-sdp-bundle-negotiation].

5.48. RFC3108: ATM SDP

[RFC3108] describes conventions for using SDP described for controlling ATM Bearer Connections, and any associated ATM Adaptation Layer (AAL).

5.48 RFC3108 Attribute Analysis
Name Notes Level Mux Category
aalType  Refer to notes below CAUTION 
eecid  Refer to notes below CAUTION 
capability  Refer to notes below CAUTION 
qosClass  Refer to notes below CAUTION 
bcob  Refer to notes below CAUTION 
stc  Refer to notes below CAUTION 
upcc  Refer to notes below CAUTION 
atmQOSparms  Refer to notes below CAUTION 
atmTrfcDesc  Refer to notes below CAUTION 
abrParms  Refer to notes below CAUTION 
abrSetup  Refer to notes below CAUTION 
bearerType  Refer to notes below CAUTION 
lij  Refer to notes below CAUTION 
anycast  Refer to notes below CAUTION 
cache  Refer to notes below CAUTION 
bearerSigIE  Refer to notes below CAUTION 
aalApp  Refer to notes below CAUTION 
cbrRate  Refer to notes below CAUTION 
sbc  Refer to notes below CAUTION 
clkrec  Refer to notes below CAUTION 
fec  Refer to notes below CAUTION 
prtfl  Refer to notes below CAUTION 
structure  Refer to notes below CAUTION 
cpsSDUsize  Refer to notes below CAUTION 
aal2CPS  Refer to notes below CAUTION 
aal2CPSSDUrate  Refer to notes below CAUTION 
aal2sscs3661unassured  Refer to notes below CAUTION 
aal2sscs3661assured  Refer to notes below CAUTION 
aal2sscs3662  Refer to notes below CAUTION 
aal5sscop  Refer to notes below CAUTION 
atmmap  Refer to notes below CAUTION 
silenceSupp  Refer to notes below CAUTION 
ecan  Refer to notes below CAUTION 
gc  Refer to notes below CAUTION 
profileDesc  Refer to notes below CAUTION 
vsel  Refer to notes below CAUTION 
dsel  Refer to notes below CAUTION 
fsel  Refer to notes below CAUTION 
onewaySel  Refer to notes below CAUTION 
codecconfig  Refer to notes below CAUTION 
isup_usi  Refer to notes below CAUTION 
uiLayer1_Prot  Refer to notes below CAUTION 
chain  Refer to notes below CAUTION 

NOTE: RFC3108 describes conventions for using SDP for characterizing ATM bearer connections using an AAL1, AAL2 or AAL5 adaptation layers. 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 RFC3108, a real-time media stream (voice, video, voiceband data, pseudo-wire, and others) or a multiplex of media streams is mapped directly into an ATM connection. RFC3108 does not address cases where ATM serves as a low-level transport pipe for IP packets which in turn can carry one or more real-time (e.g. VoIP) media sessions with a life-cycle different from that of the underlying ATM transport.

5.49. 3GPP TS 26.114

[R3GPPTS26.114] specifies IP multimedia subsystem: Media handling and interaction

5.49 3GPP TS 26.114 Attribute Analysis
Name Notes Level Mux Category
3gpp_sync_info  Usage defined for the IP Multimedia Subsystem  M NORMAL 
3gpp_MaxRecvSDUSize  Usage defined for the IP Multimedia Subsystem  M NORMAL 

5.50. 3GPP TS 183.063

[R3GPPTS183.063] Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN);

5.50 3GPP TS 183.063 Attribute Analysis
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 

5.51. 3GPP TS 24.182

[R3GPPTS24.182] specifies IP multimedia subsystem Custom Alerting tones

5.51 3GPP TS 24.182 Attribute Analysis
Name Notes Level Mux Category
g.3gpp.cat  Usage defined for the IP Multimedia Subsystem  M NORMAL 

5.52. 3GPP TS 24.183

[R3GPPTS24.183] specifies IP multimedia subsystem Custom Ringing Signal

5.52 3GPP TS 24.183 Attribute Analysis
Name Notes Level Mux Category
g.3gpp.crs  Usage defined for the IP Multimedia Subsystem  M NORMAL 

5.53. 3GPP TS 24.229

[R3GPPTS24.229] specifies IP multimedia call control protocol based on Session Initial protocol and Session Description Protocol.

5.53 3GPP TS 24.229 Attribute Analysis
Name Notes Level Mux Category
secondary-realm  secondary-realm MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow  M TRANSPORT 
visited-realm  visited-realm MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow  M TRANSPORT 
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 

5.54. ITU T.38

[T.38] defines procedures for real-time Group 3 facsimile communications over IP networks.

5.54 ITU T.38 Attribute Analysis
Name Notes Level Mux Category
T38FaxVersion  Refer to notes below  M TBD 
T38MaxBitRate  Refer to notes below  M TBD 
T38FaxFillBitRemoval  Refer to notes below  M TBD 
T38FaxTranscodingMMR  Refer to notes below  M TBD 
T38FaxTranscodingJBIG  Refer to notes below  M TBD 
T38FaxRateManagement  Refer to notes below  M TBD 
T38FaxMaxBuffer  Refer to notes below  M TBD 
T38FaxMaxDatagram  Refer to notes below  M TBD 
T38FaxUdpEC  Refer to notes below  M TBD 
T38FaxMaxIFP  Refer to notes below  M TBD 
T38FaxUdpECDepth  Refer to notes below  M TBD 
T38FaxUdpFECMaxSpan  Refer to notes below  M TBD 
T38ModemType  Refer to notes below  M TBD 
T38VendorInfo  Refer to notes below  M TBD 

NOTE: As per section 9.1 of [I-D.ietf-mmusic-sdp-bundle-negotiation], there exists no publicly available specification that defines procedures for multiplexing/demultiplexing fax protocols 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.

5.55. ITU-T Q.1970

[Q.1970] defines Bearer Independent Call Control (BICC) IP bearer control protocol.

5.55 ITU-T Q.1970 Attribute Analysis
Name Notes Level Mux Category
ipbcp  ipbcp version identifies type of IP bearer control protocol (IPBCP) message used in BICC (ITU-T Q.1901) environment which are limited to single media payload. Refer to the pertinent ITU-T specifications while multiplexing  S SPECIAL 

5.56. ITU-T H.248.15

ITU-T H.248.15 [H.248.15] defines Gateway Control Protocol SDP H.248 package attribute

5.56 ITU-T H.248.15 Attribute Analysis
Name Notes Level Mux Category
h248item  It is only applicable for 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 packaged 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  B SPECIAL 

5.57. RFC4975: The Message Session Relay Protocol

[RFC4975] 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.

5.57 RFC4975 Attribute Analysis
Name Notes Level Mux Category
accept-types  Refer to notes below  TBD 
accept-wrapped-types  Refer to notes below  TBD 
max-size  Refer to notes below  TBD 
path  Refer to notes below  TBD 

NOTE: As per section 9.1 of [I-D.ietf-mmusic-sdp-bundle-negotiation], there exists no publicly available specification that defines procedures for multiplexing/demultiplexing MRSP 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.

5.58. Historical Attributes

This section specifies analysis for the attributes that are included for historic usage alone by the [IANA].

5.58 Historical Attribute Analysis
Name Notes Level Mux Category
rtpred1  Historic attributes  M CAUTION 
rtpred2  Historic attributes  M CAUTION 

6. bwtype Attribute Analysis

This section specifies handling of specific bandwidth attributes when used in multiplexing scenarios.

6.1. RFC4566: 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.

6.1 RFC4566 bwtype Analysis
Name Notes Level Mux Category
bwtype:CT  Not Impacted  S NORMAL 
bwtype:AS  For the media level usage, the aggregate of individual bandwidth values is considered  B SUM 

6.2. RFC3556: 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 a RTP session.

6.2 RFC3556 bwtype Analysis
Name Notes Level Mux Category
bwtype:RS  Session level usage represents session aggregate and media level usage indicates SUM of the individual values while multiplexing  B SUM
bwtype:RR  Session level usage represents session aggregate and media level usage indicates SUM of the individual values while multiplexing  B SUM 

6.3. RFC3890: 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 bit-rate value together with the maximum packet rate can then be used to calculate the real bit-rate over the transport actually used.

6.3 RFC3890 bwtype Analysis
Name Notes Level Mux Category
bwtype:TIAS  The usage of TIAS is not defined under Offer/Answer usage.  B SPECIAL 
maxprate  The usage of TIAS and maxprate is not well defined under multiplexing  B SPECIAL 

NOTE: The intention of TIAS is that the media level bit-rate is multiplied with the known per-packet overhead for the selected transport and the maxprate value to determine the worst case bit-rate 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. RFC4585: 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.

7.1 RFC4585 Attribute Analysis
Name Notes Level Mux Category
ack rpsi  The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT 
ack app  Feedback parameters MUST be handled in the app specific way when multiplexed M SPECIAL 
nack  The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT 
nack pli  The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT 
nack sli  The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT 
nack rpsi  The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT 
nack app  Feedback parameters MUST be handled in the app specific way when multiplexed M SPECIAL 
trr-int  The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT 

7.2. RFC5104: 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.

7.2 RFC5104 Attribute Analysis
Name Notes Level Mux Category
ccm  The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT 

7.3. RFC6285: Unicast-Based Rapid Acquisition of Multicast RTP Sessions (RAMS)

[RFC6285] describes a method 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.

7.3 RFC6285 Attribute Analysis
Name Notes Level Mux Category
nack rai  The attribute value MUST be same for a given codec configuration  IDENTICAL-PER-PT 

7.4. RFC6679: 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.

7.4 RFC6679 Attribute Analysis
Name Notes Level Mux Category
ecn-capable-rtp  ECN markup are enabled at the RTP session level  IDENTICAL 
nack ecn  This attribute enables ECN at the RTP session level  IDENTICAL 

7.5. RFC6642: 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] memo 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.

7.5 RFC6642 Attribute Analysis
Name Notes Level Mux Category
nack tllei  The attribute value MUST be same for a given codec configuration  IDENTICAL-PER-PT 
nack pslei  The attribute value MUST be same for a given codec configuration  IDENTICAL-PER-PT 

7.6. RFC5104: 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.

7.6 RFC5104 Attribute Analysis
Name Notes Level Mux Category
ccm fir  The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT 
ccm tmmbr  The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT 
ccm tstr  The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT 
ccm vbcm  The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT 

8. group Attribute Analysis

This section analyzes SDP "group" attribute semantics [RFC5888].

8.1. RFC5888: SDP Grouping Framework

[RFC5888] defines a framework to group "m" lines in SDP for different purposes.

8.1 RFC5888 Attribute Analysis
Name Notes Level Mux Category
group:LS  Not Impacted  NORMAL 
group:FID  Not Impacted  NORMAL 

8.2. RFC3524: 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).

8.2 RFC3524 Attribute Analysis
Name Notes Level Mux Category
group:SRF  Not Impacted  NORMAL 

8.3. RFC4091: ANAT Semantics

[RFC4091] defines ANAT semantics for the SDP grouping framework. The ANAT semantics allow alternative types of network addresses to establish a particular media stream.

8.3 RFC4091 Attribute Analysis
Name Notes Level Mux Category
group:ANAT  ANAT semantics is obsoleted   CAUTION 

8.4. RFC5956: FEC Grouping Semantics in SDP

[RFC5956] defines the semantics for grouping the associated source and FEC-based (Forward Error Correction) 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, and they provide support for additive repair flows. SSRC-level (Synchronization Source) grouping semantics are also defined in this document for RTP streams using SSRC multiplexing.

8.4 RFC5956 Attribute Analysis
Name Notes Level Mux Category
group:FEC-FR  Not Impacted  NORMAL 

8.5. RFC5583: 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 the use of a layered or multiple descriptive media coding process.

8.5 RFC5583 Attribute Analysis
Name Notes Level Mux Category
group:DDP  Not Impacted  NORMAL 
depend lay  The attribute value MUST be same for a given codec configuration   M IDENTICAL-PER-PT 
depend mdc  The attribute value MUST be same for a given codec configuration  M IDENTICAL-PER-PT 

8.6. RFC7104: 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 SSRC)level are also defined in this document for RTP streams using SSRC multiplexing.

8.6 RFC7104 Attribute Analysis
Name Notes Level Mux Category
group:DUP  Not Impacted  NORMAL 

9. ssrc-group Attribute Analysis

This section analyzes "ssrc-group" semantics.

9.1. RFC5576: Source-Specific SDP Attributes

[RFC5576] defines a mechanism to describe RTP media sources, which are identified by their synchronization source (SSRC) identifiers, in SDP, to associate attributes with these sources, and to express relationships among sources. It also defines several source-level attributes that can be used to describe properties of media sources.

9.1 RFC5576 Attribute Analysis
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 

9.2. RFC7104: 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.

9.2 RFC7104 Attribute Analysis
Name Notes Level Mux Category
ssrc-group:DUP  Not Impacted  SR NORMAL 

10. QoS Mechanism Token Analysis

This section analyzes QoS tokes specified with SDP.

10.1. RFC5432: QoS Mechanism Selection in SDP

[RFC5432] defines procedures to negotiate QOS mechanisms using the SDP offer/answer model.

10.1 RFC5432 Attribute Analysis
Name Notes Level Mux Category
rsvp  rsvp attribute MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow  B TRANSPORT 
nsis  rsvp attribute MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport  B TRANSPORT 

NOTE: A single Differentiated Services Code Point (DSCP) code point per 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. RFC4566: 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.

11.1 RFC4566 Attribute Analysis
Name Notes Level Mux Category
k=  It is not recommended to use this attribute under multiplexing  S CAUTION 

12. content Attribute Analysis

12.1. RFC4796

[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.

12.1 RFC4796 Attribute Analysis
Name Notes Level Mux Category
content:slides  Not Impacted  NORMAL 
content:speaker  Not Impacted  NORMAL 
content:main  Not Impacted  NORMAL 
content:sl  Not Impacted  NORMAL 
content:alt  Not Impacted  NORMAL 

13. Payload Formats

13.1. RFC5109: 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.

13.1 RFC5109 Payload Format Analysis
Name Notes Level Mux Category
audio/ulpfec  Not recommended for multiplexing due to reuse of SSRCs  M CAUTION 
video/ulpfec  Not recommended for multiplexing due to reuse of SSRCs  M CAUTION 
text/ulpfec  Not recommended for multiplexing due to reuse of SSRCs  M CAUTION 
application/ulpfec  Not recommended for multiplexing due to reuse of SSRCs  M CAUTION 

14. Multiplexing Considerations for Encapsulating Attributes

This sections deals with recommendations for defining the multiplexing characteristics of the SDP attributes that encapsulate other SDP attributes/parameters. Such attributes as of today, 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. RFC3407: cpar Attribute Analysis

[RFC3407] capability parameter attribute (a=cpar) encapsulates 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 the above example,the category IDENTICAL is inherited for the cpar encapsulated rtcp-mux attribute.

14.2. RFC5939 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

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 Answerer's procedure to choose 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

The above allows the answerer to easily find multiplexing compatible combinations of potential configurations: The answerer simply choses 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 the example above, the potential configurations that offer transport protocol capability of RTP/SAVPF has 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 the example above, 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. RFC6871 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 ("pt") parameter 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 as described in [I-D.ietf-mmusic-sdp-bundle-negotiation], 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, 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 the example above, 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 the media capability 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 configurations, which provides configuration information that may be used to guide a subsequent offer/exchange, e.g. by adding another media stream or use alternative codec combinations not currently offered. Latent configurations have configuration numbers which 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

[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this document.]

Section 15.1 defines a new subregistry to be added by the IANA for identifying the initial registrations for various multiplexing categories applicable, as proposed in this document.

IANA is also requested to add 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 name of an entry in the existing subregistry and specify the value to be put in the new "Mux Category" column of the associated IANA registry.

15.1. New 'Multiplexing Categories' subregistry

A new sub-registry needs to be defined called the "Multiplexing Categories", with the following registrations created initially: "NORMAL", "CAUTION", "IDENTICAL", "TRANSPORT", "SUM", "INHERIT", "IDENTICAL-PER-PT", "SPECIAL" and "TBD" as defined in this document.

Initial value registration for "Multiplexing Categories".

Multiplexing Categories Reference
NORMAL  RFCXXXX
CAUTION  RFCXXXX
IDENTICAL  RFCXXXX
TRANSPORT  RFCXXXX
SUM  RFCXXXX
INHERIT  RFCXXXX
IDENTICAL-PER-PT  RFCXXXX
SPECIAL  RFCXXXX
TBD  RFCXXXX

Further entries can be registered using Standard Actions policies outlined in [RFC5226], 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 at the "Session Description Protocol (SDP) Parameters" registry.

15.2. 'Mux Category' column for subregistries

Each sub-section identifies a subregistry in 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.

For the entries in the existing subregistries, under the "Session Description Protocol (SDP) Parameters" registry, that lack a value for the "Mux Category" in this specification will get a value of "TBD".

Any future updates to the "Mux Category" column values needs to follow the existing registration policy of the affected table (Section 8.2.4.2 of [I-D.ietf-mmusic-rfc4566bis]).

Also, the procedures from Section 8.2.4.1 of [I-D.ietf-mmusic-rfc4566bis] needs to be followed when assigning "Mux Category" value for the newly defined SDP attributes.

15.2.1. Table: SDP bwtype

The following values are to be added to the 'SDP bwtype' subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references.

SDP Name Mux Category
CT  NORMAL 
AS  SUM 
RS  SUM 
RR  SUM 
TIAS  SPECIAL 

15.2.2. Table: att-field (session level)

The following values are to be added to the "att-field (session level)" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references.

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 

15.2.3. Table: att-field (both session and media level)

The following values are to be added to the "att-field (both session and media level)" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references.

NOTE: The attributes from draft-ietf-rmt-flute-sdp ('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 purposes of this specification, the multiplexing category of 'TBD' is assigned.

SDP Name Mux Category
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 
3gpp_sync_info  NORMAL 
3gpp_MaxRecvSDUSize  NORMAL 
etag  CAUTION 
duplication-delay  NORMAL 
range  CAUTION 
control  CAUTION 
mtag  CAUTION 
ts-refclk  NORMAL 
mediaclk  NORMAL 
calgextmap  NORMAL 

15.2.4. Table: att-field (media level only)

The following values are to be added to the "att-field (media level only)" registry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references.

SDP Name Mux Category
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 
all2CPS  CAUTION 
all2CPSSDUrate  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  IDENTICAL 
confid  NORMAL 
userid  NORMAL 
floorid  NORMAL 
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 
g.3gpp.cat  NORMAL 
g.3gpp.crs  NORMAL 
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 

15.2.5. Table: att-field (source level)

The following values are to be added to the "att-field (source level)" registry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references.

SDP Name Mux Category
cname  NORMAL 
previous-ssrc  NORMAL 
fmtp  IDENTICAL-PER-PT 
ts-refclk  NORMAL 
mediaclk  NORMAL 

15.2.6. Table: content SDP Parameters

The following values are to be added to the "content SDP Parameters" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references.

SDP Name Mux Category
slides  NORMAL 
speaker  NORMAL 
sl  NORMAL 
main  NORMAL 
alt  NORMAL 

15.2.7. Table: Semantics for the 'group' SDP Attribute

The following values are to be added to the "Semantics for the "group" SDP Attribute" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at 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 

15.2.8. Table: 'rtcp-fb' Attribute Values

The following values are to be added to the " 'rtcp-fb' Attribute Values" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at 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 

15.2.9. Table: 'ack' and 'nack' Attribute Values

The following values are to be added to the " 'ack' and 'nack' Attribute Values" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at 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 

15.2.10. Table: 'depend' SDP Attribute Values

The following values are to be added to the " 'depend' SDP Attribute Values" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references.

Token Mux Category
lay  IDENTICAL-PER-PT 
mdc  IDENTICAL-PER-PT 

15.2.11. Table: 'cs-correlation' Attribute Values

The following values are to be added to the " "cs-correlation" Attribute Values" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references.

Value Mux Category
callerid  TBD 
uuie  TBD 
dtmf  TBD 
external  TBD 

15.2.12. Table: Semantics for the 'ssrc-group' SDP Attribute

The following values are to be added to the Semantics for the "Semantics for the "ssrc-group" SDP Attribute" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references.

Token Mux Category
FID  NORMAL 
FEC  NORMAL 
FEC-FR  NORMAL 
DUP  NORMAL 

15.2.13. Table: SDP/RTSP key management protocol identifiers

The following values are to be added to the "SDP/RTSP key management protocol identifiers" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references.

Value Name Mux Category
mikey  IDENTICAL 

15.2.14. Table: Codec Control Messages

The following values are to be added to the "Codec Control Messages" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at 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 

15.2.15. Table: QoS Mechanism Tokens

The following values are to be added to the "QoS Mechanism Tokens" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references.

QoS Mechanism Mux Category
rsvp  TRANSPORT 
nsis  TRANSPORT 

15.2.16. Table: SDP Capability Negotiation Option Tags

The following values are to be added to the "SDP Capability Negotiation Option Tags" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at 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 

15.2.17. Table: Timestamp Reference Clock Source Parameters

The following values are to be added to the "Timestamp Reference Clock Source Parameters" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at 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 

15.2.18. Table: Media Clock Source Parameters

The following values are to be added to the "Media Clock Source Parameters" subegistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references.

Name Mux Category
sender  NORMAL 
direct  NORMAL 
IEEE1722  NORMAL 

16. Security Considerations

This document does not add any new security considerations beyond the existing considerations in the RTP RFCs ([RFC3550] and [RFC3711]) that are referenced by this specification.

The primary security for RTP including the way it is used here is described in [RFC3550] and [RFC3711].

When multiplexing SDP attributes with the category "CAUTION", the implementations should be aware of possible issues as described in this specification.

17. Acknowledgments

I would like to thank Cullen Jennings, Flemming Andreasen for suggesting the categories, contributing text and reviewing the draft. I would also link to thank Magnus Westerlund, Christer Holmberg, Jonathan Lennox, Bo Burman, Ari Keranen, and Dan Wing on suggesting structural changes helping improve the document readability.

I would like also to thank following experts on their inputs and reviews as listed - Flemming Andreasen(5.24,5.32,5.33,14), Rohan Mahy(5.57), Eric Burger(5.26),Christian Huitema(5.14), Christer Holmberg(5.21,5.26,5.51,5.52), Richard Ejzak (5.44,5.53,5.54), Colin Perkins(5.7,5.8,5.9,5.58), Magnus Westerlund(5.2,5.3,5.9,5.27,5.47,6.1,6.2,6.3,8.3,7), Roni Evens(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 (5.48,5.55), Thomas Stach.

I would like to thank Chris Lonvick for the SECDIR review, Dan Romascanu for th Gen-ART review and Sabrina Tanamal for the IANA review.

Thanks to Ben Campbell for AD review suggestions.

18. Change Log

[RFC EDITOR NOTE: Please remove this section when publishing]

Changes from draft-ietf-mmusic-sdp-mux-attributes-10 - draft-ietf-mmusic-sdp-mux-attributes-13

Changes from draft-ietf-mmusic-sdp-mux-attributes-10

Changes from draft-ietf-mmusic-sdp-mux-attributes-08 to draft-ietf-mmusic-sdp-mux-attributes-10

Changes from draft-ietf-mmusic-sdp-mux-attributes-06 to draft-ietf-mmusic-sdp-mux-attributes-08

Changes from draft-ietf-mmusic-sdp-mux-attributes-06

Changes from draft-ietf-mmusic-sdp-mux-attributes-05

Changes from draft-ietf-mmusic-sdp-mux-attributes-04

Changes from draft-ietf-mmusic-sdp-mux-attributes-03

Changes from draft-ietf-mmusic-sdp-mux-attributes-02

Changes from draft-ietf-mmusic-sdp-mux-attributes-01

Changes from draft-ietf-mmusic-sdp-mux-attributes-00

Changes from draft-nandakumar-mmusic-mux-attributes-05

Changes from draft-nandakumar-mmusic-mux-attributes-04

Changes from draft-nandakumar-mmusic-mux-attributes-03

Changes from draft-nandakumar-mmusic-mux-attributes-02

Changes from draft-nandakumar-mmusic-mux-attributes-01

Changes from draft-nandakumar-mmusic-mux-attributes-00

19. References

19.1. Normative References

[I-D.ietf-mmusic-rfc4566bis] Handley, M., Jacobson, V., Perkins, C. and A. Begen, "SDP: Session Description Protocol", Internet-Draft draft-ietf-mmusic-rfc4566bis-17, June 2016.
[I-D.ietf-mmusic-sdp-bundle-negotiation] Holmberg, C., Alvestrand, H. and C. Jennings, "Negotiating Media Multiplexing Using the Session Description Protocol (SDP)", Internet-Draft draft-ietf-mmusic-sdp-bundle-negotiation-32, August 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4566] Handley, M., Jacobson, V. and C. Perkins, "SDP: Session Description Protocol", RFC 4566, DOI 10.17487/RFC4566, July 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, DOI 10.17487/RFC5226, May 2008.

19.2. Informative References

, ", ", ", ", ", ", ", ", "
[H.248.15]Gateway control protocol: SDP H.248 package attribute"
[IANA]Session Description Protocol (SDP) Parameters"
[Q.1970]Q.1970 : BICC IP bearer control protocol"
[R3GPPTS183.063]TISPAN - IMS based ITPV Stage 3 specification."
[R3GPPTS24.182]IP Multimedia Subsystem (IMS) Customized Alerting Tones (CAT); Protocol specification"
[R3GPPTS24.183]IP Multimedia Subsystem (IMS) Customized Ringing Signal (CRS); Protocol specification"
[R3GPPTS24.229]IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP);"
[R3GPPTS26.114]IP multimedia Subsystem : Media Handling and interaction"
[RFC2326] Schulzrinne, H., Rao, A. and R. Lanphier, "Real Time Streaming Protocol (RTSP)", RFC 2326, DOI 10.17487/RFC2326, April 1998.
[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.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, DOI 10.17487/RFC3264, June 2002.
[RFC3312] Camarillo, G., Marshall, W. and J. Rosenberg, "Integration of Resource Management and Session Initiation Protocol (SIP)", RFC 3312, DOI 10.17487/RFC3312, October 2002.
[RFC3407] Andreasen, F., "Session Description Protocol (SDP) Simple Capability Declaration", RFC 3407, DOI 10.17487/RFC3407, October 2002.
[RFC3524] Camarillo, G. and A. Monrad, "Mapping of Media Streams to Resource Reservation Flows", RFC 3524, DOI 10.17487/RFC3524, April 2003.
[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.
[RFC3556] Casner, S., "Session Description Protocol (SDP) Bandwidth Modifiers for RTP Control Protocol (RTCP) Bandwidth", RFC 3556, DOI 10.17487/RFC3556, July 2003.
[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP)", RFC 3605, DOI 10.17487/RFC3605, October 2003.
[RFC3611] Friedman, T., Caceres, R. and A. Clark, "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, DOI 10.17487/RFC3611, November 2003.
[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.
[RFC3890] Westerlund, M., "A Transport Independent Bandwidth Modifier for the Session Description Protocol (SDP)", RFC 3890, DOI 10.17487/RFC3890, September 2004.
[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.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the Session Description Protocol (SDP)", RFC 4145, DOI 10.17487/RFC4145, September 2005.
[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.
[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.
[RFC4570] Quinn, B. and R. Finlayson, "Session Description Protocol (SDP) Source Filters", RFC 4570, DOI 10.17487/RFC4570, July 2006.
[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.
[RFC4574] Levin, O. and G. Camarillo, "The Session Description Protocol (SDP) Label Attribute", RFC 4574, DOI 10.17487/RFC4574, August 2006.
[RFC4583] Camarillo, G., "Session Description Protocol (SDP) Format for Binary Floor Control Protocol (BFCP) Streams", RFC 4583, DOI 10.17487/RFC4583, November 2006.
[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.
[RFC4796] Hautakorpi, J. and G. Camarillo, "The Session Description Protocol (SDP) Content Attribute", RFC 4796, DOI 10.17487/RFC4796, February 2007.
[RFC4975] Campbell, B., Mahy, R. and C. Jennings, "The Message Session Relay Protocol (MSRP)", RFC 4975, DOI 10.17487/RFC4975, September 2007.
[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.
[RFC5109] Li, A., "RTP Payload Format for Generic Forward Error Correction", RFC 5109, DOI 10.17487/RFC5109, December 2007.
[RFC5159] Dondeti, L. 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.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", RFC 5245, DOI 10.17487/RFC5245, April 2010.
[RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 2008.
[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.
[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.
[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.
[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.
[RFC5583] Schierl, T. and S. Wenger, "Signaling Media Decoding Dependency in the Session Description Protocol (SDP)", RFC 5583, DOI 10.17487/RFC5583, July 2009.
[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.
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and Control Packets on a Single Port", RFC 5761, DOI 10.17487/RFC5761, April 2010.
[RFC5762] Perkins, C., "RTP and the Datagram Congestion Control Protocol (DCCP)", RFC 5762, DOI 10.17487/RFC5762, April 2010.
[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.
[RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description Protocol (SDP) Grouping Framework", RFC 5888, DOI 10.17487/RFC5888, June 2010.
[RFC5939] Andreasen, F., "Session Description Protocol (SDP) Capability Negotiation", RFC 5939, DOI 10.17487/RFC5939, September 2010.
[RFC5956] Begen, A., "Forward Error Correction Grouping Semantics in the Session Description Protocol", RFC 5956, DOI 10.17487/RFC5956, September 2010.
[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.
[RFC6128] Begen, A., "RTP Control Protocol (RTCP) Port for Source-Specific Multicast (SSM) Sessions", RFC 6128, DOI 10.17487/RFC6128, February 2011.
[RFC6189] Zimmermann, P., Johnston, A. and J. Callas, "ZRTP: Media Path Key Agreement for Unicast Secure RTP", RFC 6189, DOI 10.17487/RFC6189, April 2011.
[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.
[RFC6230] Boulton, C., Melanchuk, T. and S. McGlashan, "Media Control Channel Framework", RFC 6230, DOI 10.17487/RFC6230, May 2011.
[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.
[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.
[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.
[RFC6364] Begen, A., "Session Description Protocol Elements for the Forward Error Correction (FEC) Framework", RFC 6364, DOI 10.17487/RFC6364, October 2011.
[RFC6642] Wu, Q., Xia, F. and R. Even, "RTP Control Protocol (RTCP) Extension for a Third-Party Loss Report", RFC 6642, DOI 10.17487/RFC6642, June 2012.
[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.
[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.
[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.
[RFC6787] Burnett, D. and S. Shanmugham, "Media Resource Control Protocol Version 2 (MRCPv2)", RFC 6787, DOI 10.17487/RFC6787, November 2012.
[RFC6849] Kaplan, H., 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.
[RFC6871] Gilman, R., Even, R. and F. Andreasen, "Session Description Protocol (SDP) Media Capabilities Negotiation", RFC 6871, DOI 10.17487/RFC6871, February 2013.
[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.
[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.
[RFC7104] Begen, A., Cai, Y. and H. Ou, "Duplication Grouping Semantics in the Session Description Protocol", RFC 7104, DOI 10.17487/RFC7104, January 2014.
[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.
[RFC7197] Begen, A., Cai, Y. and H. Ou, "Duplication Delay Attribute in the Session Description Protocol", RFC 7197, DOI 10.17487/RFC7197, April 2014.
[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.
[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.
[RFC7273] Williams, A., Gross, K., van Brandenburg, R. and H. Stokking, "RTP Clock Source Signalling", RFC 7273, DOI 10.17487/RFC7273, June 2014.
[RFC7657] Black, D. and P. Jones, Differentiated Services (Diffserv) and Real-Time Communication", RFC 7657, DOI 10.17487/RFC7657, November 2015.
[T.38]Procedures for real-time Group 3 facsimile communication over IP networks"

Author's Address

Suhas Nandakumar Cisco 170 West Tasman Drive San Jose, CA 95134 USA EMail: snandaku@cisco.com