Network Working Group S. Nandakumar
Internet-Draft Cisco
Intended status: Standards Track July 03, 2014
Expires: January 4, 2015

A Framework for SDP Attributes when Multiplexing
draft-ietf-mmusic-sdp-mux-attributes-02

Abstract

The Session Description Protocol (SDP) provides mechanisms to describe attributes of multimedia sessions and of individual media streams (e.g., Real-time Transport Protocol (RTP) sessions) within a multimedia session. In the RTCWeb WG, there is a need to use a single 5-tuple for sending and receiving media associated with multiple media descriptions ("m=" lines). Such a requirement has raised concerns over the semantic implications of the SDP attributes associated with the RTP Media Streams multiplexed over a single transport layer flow.

The scope of this specification is to provide a framework for analyzing the multiplexing characteristics of SDP attributes. The specification also categorizes existing 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 January 4, 2015.

Copyright Notice

Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.

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

Table of Contents

1. Introduction

Real-Time Communication Web (RTCWeb) framework requires Real-time Transport Protocol (RTP) as the media transport protocol and Session Description Protocol (SDP) [RFC4566] for describing and negotiating multi-media communication sessions.

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 in the IETF RTCWEB WG, a need to use a single 5-tuple for sending and receiving media associated with multiple SDP media descriptions ("m=" lines) has been identified. This would e.g. allow the usage of a single set of Interactive Connectivity Establishment (ICE) [RFC5245] candidates for multiple media descriptions. This in turn has made 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 [IANA] and possibility of new attributes being defined in the future, there is need for generic future-proof 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 applies the framework to the SDP attributes registered with the IANA [IANA]

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "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 DTLS-SRTP [RFC5763] transports for use by RTP, and conservation of ports, forms an 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] and [I-D.ietf-avt-multiplexing-rtp] 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 these 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.

As of today there are close to 250 SDP attributes registered with the IANA [IANA] and more will be added in the future. There is no clearly defined procedure to establish the validity/applicability of these attribute when used with transport multiplexing.

4. SDP Attribute Analysis Framework

Attributes in an SDP session description can be defined at the session-level and media-level. These attributes could be semantically grouped as noted below.

With the above semantic grouping as the reference, the proposed framework classifies each attribute into one of the following categories:

4.1. Category: NORMAL

Attributes that can be independently specified when multiplexing and 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: NOT RECOMMENDED

Attributes that are recommended against multiplexing since their usage under multiplexing might lead to incorrect behavior.

Example: Multiplexing media descriptions having attribute zrtp-hash defined with the media descriptions lacking it, would either complicate the handling of multiplexed streams or might fail multiplexing altogether. 

     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 3456 RTP/AVP 97 // with zrtp
     a=rtpmap:97 iLBC/8000
     <allOneLine>
     a=zrtp-hash:1.10 fe30efd02423cb054e50efd0248742ac7a52c8f91bc2
     df881ae642c371ba46df
     </allOneLine>
     m=video 34567 RTP/AVP 31 //without zrtp
     a=rtpmap:31 H261/90000

4.3. Category: IDENTICAL

Attributes that MUST be identical across all the media descriptions being multiplexed.

Attributes such as rtcp-mux fall into this category. Since RTCP reporting is done per RTP Session, RTCP Multiplexing MUST to enabled for both the audio and video m=lines in the example below 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

Attributes can be set as they are normally used but software using them in a multiplex case, MUST apply the sum of all the attributes being multiplexed instead of trying to use each one. This is typically used for bandwidth or other rate limiting attributes to the underlining 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 bytes for the given example. 

      v=0
      o=mhandley 2890844526 2890842807 IN IP4 126.16.64.4
      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

Attributes that can be set normally for multiple items in a multiplexed group but the software MUST pick just one of the attribute of the given type for use. The one chosen is the attribute associated with the "m=" line that represents the information being used for the transport of the RTP.

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

Attributes that encapsulate other SDP attributes and their multiplexing characteristics are inherited from the attributes they encapsulate. Such attributes as of today, 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. 

       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 for the cpar encapsulated rtcp-mux attribute.

4.7. Category: IDENTICAL-PER-PT

Attributes that 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.

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. 

                   
     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

Attributes where the text in the source draft must be consulted for further handling when multiplexed.

As an example, for the attribute extmap, the specification defining the extension MUST be referred to understand the multiplexing implications.

5. Analysis of Existing Attributes

This section analyzes attributes listed in IANA [IANA] grouped under the IETF document that defines them. The "Level" column indicates whether the attribute is currently specified as:

5.1. RFC4566 - SDP: Session Description Protocol

RFC4566 [RFC4566] defines the Session Description Protocol (SDP) that is intended for describing multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation

RFC4566 Attribute Analysis
Attr Name Notes Level Category
sendrecv  Not impacted  B  NORMAL 
sendonly  Not impacted  B  NORMAL 
recvonly  Not impacted  B  NORMAL 
inactive  Not impacted  B  NORMAL 
cat  Not impacted  S  NORMAL 
ptime  The attribute value must be same for a given codec configuration  M  IDENTICAL-PER-PT
maxptime  The attribute value must be same for a given codec configuration  M  IDENTICAL-PER-PT
orient  Not Impacted   M  NORMAL
framerate  The attribute value must be same for a given codec configuration  M  IDENTICAL-PER-PT 
quality  Not Impacted   M  NORMAL
rtpmap  The attribute value must be same for a given codec configuration  M  IDENTICAL-PER-PT
fmtp  The attribute value must be same for a given codec configuration  M  IDENTICAL-PER-PT
keywds  Not impacted  S  NORMAL 
type  Not Impacted   S  NORMAL 
tool  Not Impacted   S  NORMAL 
charset  Not Impacted   S  NORMAL 
sdplang  Not Impacted   B  NORMAL 
lang  Not Impacted   B  NORMAL 

5.2. RFC4585 - RTP/AVPF

RFC4585 [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.

RFC4585 Attribute Analysis
Attr Name Notes Level Category
rtcp-fb  The combination of a particular Payload Type along with the m=line identify the scope and applicability of a given RTCP feedback to a particular RTP Stream. M NORMAL 

Since RTCP feedback attributes are Payload Type (PT) scoped, the usage of identical Payload Type values across multiplexed m=lines is described in [I-D.ietf-mmusic-sdp-bundle-negotiation].

5.3. RFC5761 - Multiplexing RTP and RTCP

RFC5761 [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 Session Description Protocol (SDP) can be used to signal multiplexed sessions.

RFC5761 Attribute Analysis
Name Notes Level Category
rtcp-mux  RTP and RTCP Multiplexing affect the entire RTP Session  M  IDENTICAL 

5.4. RFC4574 - SDP Label Attribute

RFC4574 [RFC4574] defines a new Session Description Protocol (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.

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

5.5. RFC5432 - QoS Mechanism Selection in SDP

RFC5432 [RFC5432] defines procedures to negotiate QOS mechanisms using the Session Description Protocol (SDP) offer/answer model.

RFC5432 Attribute Analysis
Name Notes Level Category
qos-mech-send  A single DSCP code point per flow being multiplexed doesn't impact multiplexing since QOS mechanisms are signaled/scoped per flow.  B NORMAL 
qos-mech-recv  A single DSCP code point per flow being multiplexed doesn't impact multiplexing since QOS mechanisms are signaled/scoped per flow.  B NORMAL 

Multiplexing consideration when multiple DSCP code points are defined per flow can be found in Section 14

5.6. RFC4568 - SDP Security Descriptions

RFC4568 [RFC4568] defines a Session Description Protocol (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.

RFC4568 Attribute Analysis
Name Notes Level Category
crypto  Refer to section 6.2.5 of [I-D.ietf-mmusic-sdp-bundle-negotiation] M  SPECIAL 

If the multiplexing scheme cannot ensure unique SSRCs across all the media lines, multiplexing MUST NOT be performed.

5.7. RFC5762 - RTP over DCCP

The Real-time Transport Protocol (RTP) is a widely used transport for real-time multimedia on IP networks. The Datagram Congestion Control Protocol (DCCP) is a transport protocol that provides desirable services for real-time applications. RFC5762 [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

RFC5762 Attribute Analysis
Name Notes Current 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.  M  NOT RECOMMENDED 

If RFC6773 is being used in addition to RFC5762 and provided that DCCP-in-UDP layer has additional demultiplexing, then it may be possible to use different DCCP service codes for each DCCP flow, given each uses a different DCCP port. 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 multiplexing MUST NOT be performed even in this alternate scenario.

5.8. RFC6773 - DCCP-UDP Encapsulation

RFC6773 [RFC6773] document specifies an alternative encapsulation of the Datagram Congestion Control Protocol (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

RFC6773 Attribute Analysis
Name Notes Level Category
dccp-port  Multiplexing MUST NOT be performed due to potential conflict between the port used for DCCP en/decapsulation and the RTP.  M  NOT RECOMMENDED 

Since RFC6773 is about tunnelling 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 choosen MAY 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 MAY or MAY NOT work depending on the nature of DCCP encapsulations and ports choses thus rendering it to be very application dependant.

5.9. RFC5506 - Reduced-Size RTCP in RTP Profile

RFC5506 [RFC5506] discusses benefits and issues that arise when allowing Real-time Transport Protocol (RTCP) packets to be transmitted with reduced size.

RFC5506 Attribute Analysis
Name Notes Level Category
rtcp-rsize  Reduced size RTCP affects the entire RTP Session  M  IDENTICAL 

5.10. 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 Session Initiation Protocol (SIP), to coordinate MRCPv2 clients and servers and manage sessions between them, and the Session Description Protocol (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 [RFC6787] defines attributes for this purpose.

RFC6787 Attribute Analysis
Name Notes Level Category
resource  Not Impacted  M  NORMAL 
channel  Not Impacted  M  NORMAL 

5.11. RFC5245 - Interactive Connectivity Establishment (ICE)

RFC5245 [RFC5245] describes a protocol for Network Address Translator(NAT) traversal for UDP-based multimedia sessions established with the offer/answer model. This protocol is called Interactive Connectivity Establishment (ICE). 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 Session Initiation Protocol (SIP).

RFC5245 Attribute Analysis
Name Notes Level Category
ice-lite  Not Impacted  S NORMAL 
ice-options  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 

5.12. RFC5285 - RTP Header Extensions

RFC5285 [RFC5285] provides a general mechanism to use the header extension feature of RTP (the Real-Time Transport Protocol). 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.

RFC5285 Attribute Analysis
Name Notes Level Category
extmap  Specific RTP extension document MUST be referred  B SPECIAL 

5.13. 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.

RFC3605 Attribute Analysis
Name Notes Level Category
rtcp  Identical attribute value MUST be used since the RTCP port affects the entire RTP session.  M IDENTICAL 

5.14. RFC5576 - Source-Specific SDP Attributes

RFC5576 [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.

RFC5576 Attribute Analysis
Name Notes Level Category
ssrc  Refer to Notes below  M NORMAL 
ssrc-group  Refer to section Section 9 for specific analysis of the grouping semantics  M SPECIAL 
cname  Not Impacted [Open Issues: what are the rules for CNAME duplication across sessions?]  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 

If SSRCs are repeated across m=lines being multiplexed, they MUST all represent the same underlying RTP Source. For more details on implications of SSRC values with in the context of multiplexing please refer to [I-D.ietf-mmusic-sdp-bundle-negotiation]

5.15. RFC6236 - Image Attributes in SDP

RFC6236 [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.

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

5.16. RFC6285 - Rapid Acquisition of Multicast RTP Sessions

RFC6285 [RFC6285] describes a method using the existing RTP and RTP Control Protocol (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.

RFC6285 Attribute Analysis
Name Notes Level Category
rams-updates  Not recommended   M  NOT RECOMMENDED 

5.17. RFC6230 - Media Control Channel Framework

RFC6230 [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 the Session Initiation Protocol (SIP) to establish an application-level control mechanism between application servers and associated external servers such as media servers.

RFC6230 Attribute Analysis
Name Notes Level Category
cfw-id  Not Applicable  M  NORMAL 

5.18. RFC6364 - SDP Elements for FEC Framework

RFC6364 [RFC6364] specifies the use of the Session Description Protocol (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.

RFC6364 Attribute Analysis
Name Notes Level Category
fec-source-flow  M  SPECIAL 
fec-repair-flow  M  SPECIA: 
repair-window  M  SPECIAL 

5.19. RFC4796 - Content Attribute

RFC4796 [RFC4796] defines a new Session Description Protocol (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.

RFC4796 Attribute Analysis
Name Notes Level Category
content  Not Impacted  M  NORMAL 

5.20. RFC3407 - SDP Simple Capability Declaration

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

RFC3407 Attribute Analysis
Name Notes Level Category
sqn  Not Impacted  B NORMAL 
cdsc  Not Impacted.  B NORMAL 
cpar  Refer to Section 15  B INHERIT 
cparmin  Refer to notes below   B SPECIAL 
cparmax  Refer to notes below  B SPECIAL 

Since the attributes (a=cparmin and a=cparmax) defines minimum and maximum numerical values associated with the attributed described in a=cpar, it is recommended to consult the document defining the attribute for dealing under media stream multiplexing.

5.21. RFC6284 - Port Mapping between Unicast and Multicast RTP Sessions

RFC6284 [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

RFC6284 Attribute Analysis
Name Notes Level Category
portmapping-req  Not recommended, if port mapping is required by the application  M  NOT RECOMMENDED 

5.22. RFC6714 - MSRP-CEMA

RFC6714 [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 Session Description Protocol (SDP) attribute, 'msrp-cema', that MSRP endpoints use to indicate support of the CEMA extension.

RFC6714 Attribute Analysis
Name Notes Level Category
msrp-cema  Not Impacted  M  NORMAL 

5.23. RFC4583 - SDP Format for BFCP Streams

RFC4583 [RFC4583] document specifies how to describe Binary Floor Control Protocol (BFCP) streams in Session Description Protocol (SDP) descriptions. User agents using the offer/answer model to establish BFCP streams use this format in their offers and answers

RFC4583 Attribute Analysis
Name Notes Level Category
floorctrl  Must be repeated across all the multiplexed m=lines  M  IDENTICAL 
confid  Not Impacted  M  NORMAL 
userid  Not Impacted  M  NORMAL 
floorid  The floorid MUST be globally unique  M  NORMAL 

5.24. RFC5547 - SDP Offer/Answer for File Transfer

RFC5547 [RFC5547] provides a mechanism to negotiate the transfer of one or more files between two endpoints by using the Session Description Protocol (SDP) offer/answer model specified in [RFC3264].

RFC5547 Attribute Analysis
Name Notes Level Category
file-selector  Not Impacted  M NORMAL 
file-transfer-id  Not Impacted  M NORMAL 
file-disposition  Not Impacted  M NORMAL 
file-date  Not Impacted  M NORMAL 
file-iconfile-range  Not Impacted  M NORMAL 

5.25. RFC6489 - SDP and RTP Media Loopback Extension

[MEDIA_LOOPBACK] 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 VoIP, Real-time Text and Video over IP performance metrics.

An Extension to the Session Description Protocol (SDP) and Real-time Transport Protocol (RTP) for Media Loopback
Name Notes Level Category
loopback rtp-pkt-loopback  Not Impacted   M NORMAL 
loopback rtp-media-loopback  Not Impacted   M NORMAL 
loopback-source  Not Impacted  M NORMAL 
loopback-mirror  Not Impacted  M NORMAL 

5.26. RFC5760 - RTCP with Unicast Feedback

RFC5760 [RFC5760] specifies an extension to the Real-time Transport Control Protocol (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.

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

5.27. RFC3611 - RTCP XR

RFC3611 [RFC3611] defines the Extended Report (XR) packet type for the RTP Control Protocol (RTCP), and defines how the use of XR packets can be signaled by an application if it employs the Session Description Protocol (SDP).

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

5.28. RFC5939 - SDP Capability Negotiation

RFC5939 [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.

RFC5939 Attribute Analysis
Name Notes Level Category
pcfg  Refer to section Section 15   M INHERIT 
acfg  Refer to section Section 15  M INHERIT 
csup  Not Impacted  B NORMAL 
creq  Not Impacted  B NORMAL 
acap  Refer to section Section 15  B INHERIT 
tcap  Refer to section Section 15  B INHERIT 

5.29. RFC6871- SDP Media Capabilities Negotiation

Session Description Protocol (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.

Session Description Protocol (SDP) Media Capabilities Negotiation
Name Notes Level Category
rmcap  Refer to section Section 15  B INHERIT 
omcap  Refer to section Section 15  B INHERIT 
mfcap  Refer to section Section 15  B INHERIT 
mscap  Refer to section Section 15  B INHERIT 
lcfg  Not Impacted  B NORMAL 
sescap  Refer to section Section 15  S INHERIT 

5.30. RFC4567 - Key Management Extensions for SDP and RTSP

RFC4567 [RFC4567] defines general extensions for Session Description Protocol (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.

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

5.31. RFC4572 - Comedia over TLS in SDP

RFC4572 [RFC4572] specifies how to establish secure connection-oriented media transport sessions over the Transport Layer Security (TLS) protocol using the Session Description Protocol (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.

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

5.32. RFC4570 - SDP Source Filters

RFC4570 [RFC4570] describes how to adapt the Session Description Protocol (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

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

5.33. RFC6128 - RTCP Port for Multicast Sessions

The Session Description Protocol (SDP) has an attribute that allows RTP applications to specify an address and a port associated with the RTP Control Protocol (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 [RFC6128] removes this restriction by introducing a new SDP attribute.

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

5.34. RFC6189 - ZRTP

RFC6189 [RFC6189] defines ZRTP, a protocol for media path Diffie-Hellman exchange to agree on a session key and parameters for establishing unicast Secure Real-time Transport Protocol (SRTP) sessions for Voice over IP (VoIP) applications.

RFC6189 Attribute Analysis
Name Notes Level Category
zrtp-hash  Complicates if all the m=lines are not authenticated as given in the example below  M NOT RECOMMENDED  
     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 3456 RTP/AVP 97
     a=rtpmap:97 iLBC/8000
     <allOneLine>
     a=zrtp-hash:1.10 fe30efd02423cb054e50efd0248742ac7a52c8f91bc2
     df881ae642c371ba46df
     </allOneLine>
     m=video 34567 RTP/AVP 31
     a=rtpmap:31 H261/90000

Example: Multiplexing media descriptions having attribute zrtp-hash defined with the media descriptions lacking it, would either complicate the handling of multiplexed stream or fail multiplexing.

5.35. RFC4145 - Connection-Oriented Media

RFC4145 [RFC4145] describes how to express media transport over TCP using the Session Description Protocol (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.

RFC4145 Attribute Analysis
Name Notes Level Category
setup  MUST be identical across all m=lines  B IDENTICAL 
connection  MUST be identical across all m=lines  B IDENTICAL 

5.36. RFC5159 - OMA BCAST SDP Attributes

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

RFC5159 Attribute Analysis
Name Notes Level Category
bcastversion  Not Impacted  S NORMAL 
stkmstream  Not Impacted  B NORMAL 
SRTPAuthentication  Not Impacted  M NORMAL 
SRTPROCTxRate  Not Impacted  M NORMAL 

5.37. RFC6193 - Media Description for IKE in SDP

RFC6193 [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 the Session Description Protocol (SDP) so that it can negotiate use of the Internet Key Exchange Protocol (IKE) for media sessions in the SDP offer/answer model.

RFC6193 Attribute Analysis
Name Notes Level Category
ike-setup  Attribute MUST be identical across all the m=lines  B IDENTICAL 
psk-fingerprint  Attribute MUST be identical across all the m=lines  B IDENTICAL 
ike-esp  Attribute MUST be identical across all the m=lines  B IDENTICAL 
ike-esp-udpencap  Attribute MUST be identical across all the m=lines  B IDENTICAL 

With the above SDP constraints, a session multiplexed with multiple m=lines will use only one IPSec association for all of the m= lines.

5.38. RFC6064 - SDP and RTSP Extensions for 3GPP

The Packet-switched Streaming Service (PSS) and the Multimedia Broadcast/Multicast Service (MBMS) defined by 3GPP use the Session Description Protocol (SDP) and Real Time Streaming Protocol (RTSP) with some extensions. RFC6064 [RFC6064] provides information about these extensions and registers the RTSP and SDP extensions with IANA.

RFC6064 Attribute Analysis
Name Notes Level Category
X-predecbufsize  Refer to notes below  M NOT RECOMMENDED 
X-initpredecbufperiod  Refer to notes below  M NOT RECOMMENDED 
X-initpostdecbufperiod  Refer to notes below  M NOT RECOMMENDED 
X-decbyterate Refer to notes below  M NOT RECOMMENDED 
3gpp-videopostdecbufsize  Refer to notes below  M NOT RECOMMENDED 
framesize The attribute value must be same for a given codec configuration  M IDENTICAL-PER-PT 
3GPP-Integrity-Key  Refer to notes below  S NOT RECOMMENDED 
3GPP-SRTP-Config  Refer to notes below   M NOT RECOMMENDED 
alt,alt-default-id  Refer to notes below  M NOT RECOMMENDED 
alt-group  Refer to notes below  M NOT RECOMMENDED 
3GPP-Adaptation-Support  Refer to notes below   M NOT RECOMMENDED 
3GPP-Asset-Informatio  Refer to notes below  B NOT RECOMMENDED 
mbms-mode  Refer to notes below  B NOT RECOMMENDED 
mbms-flowid  MRefer to notes below  M NOT RECOMMENDED 
mbms-repair  Refer to notes below  B NOT RECOMMENDED 
3GPP-QoE-Metrics:Corruption duration  Refer to notes below  M NOT RECOMMENDED 
3GPP-QoE-Metrics:Rebuffering duration  Refer to notes below  M NOT RECOMMENDED 
3GPP-QoE-Metrics:Initial buffering duration  Refer to notes below  M NOT RECOMMENDED 
3GPP-QoE-Metrics:Successive loss of RTP packets  Refer to notes below  M NOT RECOMMENDED 
3GPP-QoE-Metrics:Frame rate deviation  Refer to notes below  M NOT RECOMMENDED 
3GPP-QoE-Metrics:Jitter duration  Refer to notes below  M NOT RECOMMENDED 
3GPP-QoE-Metrics:Content Switch Time  Refer to notes below  B NOT RECOMMENDED 
3GPP-QoE-Metrics:Average Codec Bitrat  Refer to notes below  M NOT RECOMMENDED 
3GPP-QoE-Metrics:Codec Information  Refer to notes below  M NOT RECOMMENDED 
3GPP-QoE-Metrics:Buffer Status  Refer to notes below  M NOT RECOMMENDED 

[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].

5.39. RFC3108 - ATM SDP

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

RFC3108 Attribute Analysis
Name Notes Level Category
aalType  Not Impacted B  NORMAL 
eecid  Not Impacted B  NORMAL 
aalType  Not Impacted B  NORMAL 
capability  Not Impacted B  NORMAL 
qosClass  Not Impacted B  NORMAL 
bcob  Not Impacted B  NORMAL 
stc  Not Impacted B  NORMAL 
upcc  Not Impacted B  NORMAL 
atmQOSparms  Not Impacted B  NORMAL 
atmTrfcDesc  Not Impacted B  NORMAL 
abrParms  Not Impacted B  NORMAL 
abrSetup  Not Impacted B  NORMAL 
bearerType  Not Impacted B  NORMAL 
lij  Not Impacted B  NORMAL 
anycast  Not Impacted B  NORMAL 
cache  Not Impacted B  NORMAL 
bearerSigIE  Not Impacted B  NORMAL 
aalApp  Not Impacted B  NORMAL 
cbrRate  Not Impacted B  NORMAL 
sbc  Not Impacted B  NORMAL 
clkrec  Not Impacted B  NORMAL 
fec  Not Impacted B  NORMAL 
prtfl  Not Impacted B  NORMAL 
structure  Not Impacted B  NORMAL 
cpsSDUsize  Not Impacted B  NORMAL 
aal2CPS  Not Impacted B  NORMAL 
aal2CPSSDUrate  Not Impacted B  NORMAL 
aal2sscs3661unassured  Not Impacted B  NORMAL 
aal2sscs3661assured  Not Impacted B  NORMAL 
aal2sscs3662  Not Impacted B  NORMAL 
aal5sscop  Not Impacted B  NORMAL 
atmmap  Not Impacted B  NORMAL 
silenceSupp  Not Impacted B  NORMAL 
ecan  Not Impacted B  NORMAL 
gc  Not Impacted B  NORMAL 
profileDesc  Not Impacted B  NORMAL 
vsel  Not Impacted B  NORMAL 
dsel  Not Impacted B  NORMAL 
fsel  Not Impacted B  NORMAL 
onewaySel  Not Impacted B  NORMAL 
codecconfig  Not Impacted B  NORMAL 
isup_usi  Not Impacted B  NORMAL 
isup_usi  Not Impacted B  NORMAL 
chain  Not Impacted B  NORMAL 

RFC3108 describes conventions for using the Session Description Protocol (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 may be multiplexed into a bearer connection. For all adaptation types (AAL1, AAL2 and AAL5), bearer connections may 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 may carry one or more real-time (e.g. VoIP) media sessions with a life-cycle different from that of the underlying ATM transport.

5.40. 3GPP TS 24.182

3GPP TS 24.182 [R3GPPTS24.182] specifies IP multimedia subsystem Custom Alerting tones

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

5.41. 3GPP TS 24.183

3GPP TS 24.183 [R3GPPTS24.183]specifies IP multimedia subsystem Custom Ringing Signal

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

5.42. 3GPP TS 24.229

3GPP TS 24.229 [R3GPPTS24.229]IP multimedia call control protocol based on Session Initial protocol and Session Description Protocol.

3GPP TS 24.229 Attribute Analysis
Name Notes Level Category
secondary-realm  Per media-level attribute MUST be used per underlying transport  M TRANSPORT 
visited-realm  Per media-level attribute MUST be used per underlying transport  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-bw  Not Impacted  M NORMAL 
omr-s-bw  Not Impacted  M NORMAL 
omr-m-att  Not Impacted  M NORMAL 
omr-codecs  Not Impacted  M NORMAL 

5.43. ITU T.38

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

Historic Attribute Analysis
Name Notes Level Category
T38FaxVersion  Not Impacted  S NORMAL 
T38MaxBitRate  Not Impacted  S NORMAL 
T38FaxFillBitRemoval  Not Impacted  S NORMAL 
T38FaxTranscodingMMR  Not Impacted  S NORMAL 
T38FaxTranscodingJBIG  Not Impacted  S NORMAL 
T38FaxRateManagement  Not Impacted  S NORMAL 
T38FaxMaxBuffer  Not Impacted  S NORMAL 
T38FaxMaxDatagram  Not Impacted  S NORMAL 
T38FaxUdpEC  Not Impacted  S NORMAL 

The ITU T.38 attributes are clearly unaffected by multiplexing and are specific to the working of the fax protocol itself.

5.44. ITU-T H.248.15

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

Historic Attribute Analysis
Name Notes Level Category
h248item  It is also 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 may 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 

5.45. RFC4975 - The Message Session Relay Protocol

RFC4975 [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.

RFC4975 Attribute Analysis
Name Notes Level Category
accept-types  Not Impacted  M  NORMAL 
accept-wrapped-types  Not Impacted  M  NORMAL 
max-size  Not Impacted  M  NORMAL 
path  Not Impacted  M  NORMAL 

5.46. Historical

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

Unknowns Attribute Analysis
Name Notes Level Category
rtpred1  Historic attributes.  Not-Applcable NOT RECOMMENDED 
rtpred2  Historic attributes.  Not-Applcable NOT RECOMMENDED 
PSCid  Not Applicable  Not-Applcable TBD 
bc_service  Not Applicable  Not-Applcable TBD 
bc_program  Not Applicable  Not-Applcable TBD 
bc_service_package  Not Applicable  Not-Applcable TBD 

6. bwtype Attribute Analysis

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

6.1. RFC4566 - SDP: Session Description Protocol

RFC4566 bwtype Analysis
Name Notes Level Category
bwtype:CT  Aggregate bandwidth for the conference  S NORMAL 
bwtype:AS  As a session attribute, it specifies the session aggregate unless media-level b=RR and/or b=RS attributes are used. Under this interpretation the multiplexing scheme has no impact and thus NORMAL category applies.  B 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 [RFC3556] defines an extension to the Session Description Protocol (SDP) to specify two additional modifiers for the bandwidth attribute. These modifiers may be used to specify the bandwidth allowed for RTP Control Protocol (RTCP) packets in a Real-time Transport Protocol (RTP) session

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

6.3. RFC3890 - Bandwidth Modifier for SDP

RFC3890 [RFC3890] defines a Session Description Protocol (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.

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

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. This still ignores the fact that this is a send side declaration, and not intended for receiver negotiation.

7. rtcp-fb Attribute Analysis

This section analyzes rtcp-fb SDP attributes [RTCP-FB].

7.1. RFC4585 - RTP/AVPF

RFC4585 [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.

RFC4585 Attribute Analysis
Attr Name Notes Level Category
ack rpsi  Not Impacted M NORMAL 
ack app  Feedback parameters MUST be handled in the app specific way when multiplexed M SPECIAL 
nack  Not Impacted M NORMAL 
nack pli  Not Impacted M NORMAL 
nack sli  Not Impacted M NORMAL 
nack rpsi  Not Impacted M NORMAL 
nack app  Feedback parameters MUST be handled in the app specific way when multiplexed M SPECIAL 
trr-int  This attribute applies to RTP Session as a whole M IDENTICAL 

7.2. RFC5104 - Codec Control Messages in AVPF

RFC5104 [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.

RFC5104 Attribute Analysis
Attr Name Notes Level Category
ccm  Not Impacted M Normal 

7.3. RFC6285 - Unicast-Based RAMS

RFC6285 Attribute Analysis
Name Notes Level Category
nack rai  Not Impacted  M  NORMAL 

7.4. RFC6679 - ECN for RTP over UDP/IP

RFC6679 [RFC6679] specifies how Explicit Congestion Notification (ECN) can be used with the Real-time Transport Protocol (RTP) running over UDP, using the RTP Control Protocol (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 Session Traversal Utilities for NAT (STUN) extension used in the optional initialization method using Interactive Connectivity Establishment (ICE)

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

7.5. RFC6642 - Third-Party Loss Report

In a large RTP session using the RTP Control Protocol (RTCP) feedback mechanism defined in RFC 4585 [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 [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 Session Description Protocol (SDP) signaling is also defined.

RFC6642 Attribute Analysis
Name Notes Level Category
nack tllei  Not Impacted  M  NORMAL 
nack pslei  Not Impacted  M  NORMAL 

7.6. RFC5104 - Codec Control Messages in AVPF

RFC5104 Attribute Analysis
Attr Name Notes Level Category
ccm fir  Not Impacted M NORMAL 
ccm tmmbr  Not Impacted M NORMAL 
ccm tstr  Not Impacted M NORMAL 
ccm vbcm  Not Impacted M NORMAL 

8. group Attribute Analysis

This section analyzes SDP "group" semantics [GROUP-SEM].

8.1. RFC5888 - SDP Grouping Framework

RFC5888 [RFC5888] defines a framework to group "m" lines in the Session Description Protocol (SDP) for different purposes.

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

8.2. RFC3524 - Mapping Media Streams to Resource Reservation Flows

RFC3524 [RFC3524] defines an extension to the Session Description Protocol (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).

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

8.3. RFC4091 - ANAT Semantics

RFC4091 [RFC4091] defines the Alternative Network Address Types (ANAT) semantics for the Session Description Protocol (SDP) grouping framework. The ANAT semantics allow alternative types of network addresses to establish a particular media stream.

RFC4091 Attribute Analysis
Name Notes Level Category
group:ANAT  ANAT semantics is obseleted  S  NOT RECOMMENDED 

8.4. RFC5956 - FEC Grouping Semantics in SDP

RFC5956 [RFC5956] defines the semantics for grouping the associated source and FEC-based (Forward Error Correction) repair flows in the Session Description Protocol (SDP). The semantics defined in the document are to be used with the SDP Grouping Framework (RFC 5888). 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 Real-time Transport Protocol (RTP) streams using SSRC multiplexing.

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

8.5. RFC5583 - Signaling Media Decoding Dependency in SDP

RFC5583 [RFC5583] defines semantics that allow for signaling the decoding dependency of different media descriptions with the same media type in the Session Description Protocol (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.

RFC5583 Attribute Analysis
Name Notes Level Category
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 

The usage of identical Payload Type values across multiplexed m=lines is described in [I-D.ietf-mmusic-sdp-bundle-negotiation].

9. ssrc-group Attribute Analysis

This section analyzes "ssrc-group" semantics [SSRC-GROUP].

9.1. RFC5576 - Source-Specific SDP Attributes

RFC5576 Attribute Analysis
Name Notes Level Category
FID  Not Impacted  M NORMAL 
FEC  Not Impacted  M NORMAL 
FEC-FR  Not Impacted  M NORMAL 

10. QoS Mechanism Token Analysis

This section analyzes QoS tokes specified with SDP[QOS].

10.1. RFC5432 - QoS Mechanism Selection in SDP

RFC5432 Attribute Analysis
Name Notes Level Category
rsvp  Not Impacted, since QOS mechanisms are applied per flow.  B NORMAL 
nsis  Not Impacted, since QOS mechanisms are applied per flow.  B NORMAL 

11. k= Attribute Analysis

11.1. RFC4566 SDP: Session Description Protocol

RFC4566 Attribute Analysis
Name Notes Level Category
k=  It is NOT recommended to use this attribute  S NOT RECOMMENDED 

12. content Atribute Analysis

12.1. RFC4796

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

13. Payload Formats

13.1. RFC5109 - RTP Payload Format for Generic FEC

RFC5109 [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.

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

Draft draft-lennox-payload-ulp-ssrc-mux proposes a simple fix to make it possible to use ULP with multiplexing and ULP is allowed when used with that.

14. Multiplexing Media Streams and DSCP Markings

Note: This section does not yet have WG consensus but is included as a proposal to the WG. There are two options being proposed, A and B. The authors suggest A.

14.1. Option A

This section provides two rules for multiplexing multiple media streams with DSCP markings over a single 5-tuple.

For WebRTC applications following the advice in [I-D.dhesikan-tsvwg-rtcweb-qos], the above rules end up allowing the audio and video to be multiplexed in many, but not all, cases.

14.2. Option B

Media Streams MAY be multiplexed regardless of what the setting of the DSCP Per Hop Behavior group (PHB).

15. 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.

15.1. 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 referenced 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.

15.2. 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

15.2.1. Recommendations

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.

15.2.1.1. Recommendation-1: Transport Capability Analysis

When a transport capability is proposed as a potential configuration under a given media description, it is recommended that all the media descriptions under multiplexing have the same potential configuration number for the given transport capability. 

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.

15.2.1.2. Recommendation-2: Attribute Capability Analysis

For attribute capabilities which are offered as potential configurations that encapsulate attributes whose value MUST be IDENTICAL under multiplexing, it is recommended that all the media descriptions under multiplexing have the same potential configuration number for the given attribute capability. 

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.

15.2.1.3. Recommendation-3: Sescap Attribute Analysis

It is recommended that any bundled media descriptions/configurations are also acceptable combinations of media streams/configurations as specified by "sescap" attribute.

15.2.1.4. Recommendation-4: Capability Extension Attributes

Since it is nearly impossible to define a generic mechanism for various capability extensions , this document does't provide procedures for dealing with the capability extension attributes. However, Section Section 15.3 provide analysis of media capability extension attributes as defined in [RFC6871].

15.3. RFC6871 Analysis

[RFC6871] extends 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.

Building upon the analysis from the previous section, following recommendation is provided for dealing with the attributes defined in [RFC6871] under multiplexing

15.3.1. Recommendation-5: Attribute Capability Under Shared Payload Type

For attribute capabilities which are offered as potential configurations that encapsulate attributes whose value MUST be IDENTICAL-PER-PT under multiplexing, it is recommended that all the media descriptions under multiplexing have the same potential configuration number for the given attribute capability

The attributes (a=rmcap, a=mfcap) follow the above recommendations under mutliplexing 

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 97. 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

15.4. Recommendation-6: Offer/Answer Negotiation Expectations

For attributes encapsulated via "a=acap", "a=omcap", "a=mscap" capability attributes and presented as part of potential/actual configurations during the Offer/Answer negotiation prodecure, the negotiation MUST ensure that the multiplexing behavior of these capabilities inherit from the behavior of the attribute being encapsulated.

Example 1: Below SDP example captures the following aspects. 

<Offer-SDP>
v=0
o=- 25678 753849 IN IP4 192.0.2.1
s=
t=0 0
c=IN IP4 192.0.2.1
m=audio 3456 RTP/AVP 98
a=tcap:1 RTP/SAVPF
a=rtpmap:98 OPUS/48000/2
a=pcfg:1 t=1
m=video 51372 RTP/AVP 101
a=rtpmap:101 H264/90000
a=tcap:2 RTP/SAVPF RTP/AVPF
a=pcfg:2 t=2|3

<Valid Answer>
v=0
o=- 24351 621814 IN IP4 192.0.2.2
s=
m=audio 3456 RTP/SAVPF 98
a=rtpmap:98 OPUS/48000/2
a=acfg:1 t=1

m=video 51372 RTP/SAVPF 101
a=rtpmap:101 H264/90000
a=acfg:2 t=2

<Invalid Answer>
v=0
o=- 24351 621814 IN IP4 192.0.2.2
s=
m=audio 3456 RTP/SAVPF 98
a=rtpmap:98 OPUS/48000/2
a=acfg:1 t=1

m=video 51372 RTP/AVPF 101
a=rtpmap:101 H264/90000
a=acfg:2 t=3

16. IANA Considerations

IANA shall register categories from this specification by expanding the Session Description Protocol (SDP) Parameters table with a column listing categories against each SDP parameter.

+---------------------+
| Category            |
+---------------------+
| NORMAL              |
+---------------------+
| NOT RECOMMENDED     |
+---------------------+
| IDENTICAL           |
+---------------------+
| TRANSPORT           |
+---------------------+
| INHERIT             |
----------------------+
| IDENTICAL-PER-PT    |
+---------------------+
| SPECIAL             |
----------------------

17. Security Considerations

All the attributes which involve security key needs a careful review to ensure two-time pad vulnerability is not created.

18. Acknowledgments

I would like to thank Cullen Jennings for suggesting the categories, contributing text and reviewing the draft. I would also link to thank Magnus, Christer, Jonathan Lennox, Bo Burman, and Dan 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(5.20,5.28,5.29,15), Rohan Mahy(5.45), Eric Burger(5.22),Christian Huitema(5.13), Christer Holmberg(5.17,5.22,5.40,5.41), Richard Ejzak (5.36,5.42,5.43,5.44), Colin Perkins(5.7,5.8), Magnus westerlund(5.2,5.3,5.9,5.26, 5.27,6.1,6.2,6.3,8.3,7), Roni Evens(5.12,5.27,8.4), Subha Dhesikan(5.5,12.1,14), Dan Wing(5.6,5.11,5.30,5.34,5.37), Ali C Begen(5.1,5.16,5.18,5.21,5.33,8.2,8.4,13.1), Bo Burman (7.2,7.6), Charles Eckel(5.14,5.23,5.24,9.1,8.5), Paul Kyzivat(5.24), Ian Johansson(5.15), Saravanan Shanmugham(5.10), Paul E Jones(5.25), Rajesh Kumar(5.39), Jonathan Lennox(5.31,5,14,11.1), Mo Zanaty(5.4,5.19,8.1,8.3,8.5,12.1), Christian Huitema (5.13), Qin Wu (5.38 PM-Dir review).

19. Change Log

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

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

20. References

20.1. Normative References

[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, July 2006.

20.2. Informative References

, ", ", ", ", ", ", ", ", ", ", ", "
[ACK-NACK]S Description Protocol (SDP) RTCP ACK/NACK Feedback attributes", .
[CCM]S Description Protocol (SDP) RTCP-FB Codec Control Messages", .
[GROUP-SEM]S Description Protocol (SDP) "group" semantics", .
[H.248.15]Gateway control protocol: SDP H.248 package attribute", .
[I-D.dhesikan-tsvwg-rtcweb-qos] Dhesikan, S., Druta, D., Jones, P. and J. Polk, "DSCP and other packet markings for RTCWeb QoS", Internet-Draft draft-dhesikan-tsvwg-rtcweb-qos-02, July 2013.
[I-D.ietf-avt-multiplexing-rtp] El-Khatib, K., Luo, G., Bochmann, G. and Pinjiang. Feng, "Multiplexing Scheme for RTP Flows between Access Routers", Internet-Draft http://tools.ietf.org/html/draft-ietf-avt-multiplexing-rtp-01, October 1999.
[I-D.ietf-mmusic-sdp-bundle-negotiation] Holmberg, C., Alvestrand, H. and C. Jennings, "Multiplexing Negotiation Using Session Description Protocol (SDP) Port Numbers", Internet-Draft draft-ietf-mmusic-sdp-bundle-negotiation-03, February 2013.
[IANA]S Description Protocol (SDP) Parameters", .
[MEDIA_LOOPBACK] 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", Internet-Draft 6489, January 2013.
[QOS]S Description Protocol (SDP) QoS Mechanism Tokens", .
[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);", .
[RFC3108] Kumar, R. and M. Mostafa, "Conventions for the use of the Session Description Protocol (SDP) for ATM Bearer Connections", RFC 3108, May 2001.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002.
[RFC3407] Andreasen, F., "S Description Protocol (SDP) Simple Capability Declaration", RFC 3407, October 2002.
[RFC3524] Camarillo, G. and A. Monrad, "Mapping of Media Streams to Resource Reservation Flows", RFC 3524, April 2003.
[RFC3556] Casner, S., "S Description Protocol (SDP) Bandwidth Modifiers for RTP Control Protocol (RTCP) Bandwidth", RFC 3556, July 2003.
[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP)", RFC 3605, October 2003.
[RFC3611] Friedman, T., Caceres, R. and A. Clark, "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, November 2003.
[RFC3890] Westerlund, M., "A Transport Independent Bandwidth Modifier for the Session Description Protocol (SDP)", RFC 3890, 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, June 2005.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the Session Description Protocol (SDP)", RFC 4145, 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, July 2006.
[RFC4568] Andreasen, F., Baugher, M. and D. Wing, "S Description Protocol (SDP) Security Descriptions for Media Streams", RFC 4568, July 2006.
[RFC4570] Quinn, B. and R. Finlayson, "S Description Protocol (SDP) Source Filters", RFC 4570, July 2006.
[RFC4572] Lennox, J., "Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP)", RFC 4572, July 2006.
[RFC4574] Levin, O. and G. Camarillo, "The Session Description Protocol (SDP) Label Attribute", RFC 4574, August 2006.
[RFC4583] Camarillo, G., "S Description Protocol (SDP) Format for Binary Floor Control Protocol (BFCP) Streams", RFC 4583, 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, July 2006.
[RFC4796] Hautakorpi, J. and G. Camarillo, "The Session Description Protocol (SDP) Content Attribute", RFC 4796, February 2007.
[RFC4975] Campbell, B., Mahy, R. and C. Jennings, "The Message Session Relay Protocol (MSRP)", RFC 4975, 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, February 2008.
[RFC5109] Li, A., "RTP Payload Format for Generic Forward Error Correction", RFC 5109, December 2007.
[RFC5159] Dondeti, L. and A. Jerichow, "S Description Protocol (SDP) Attributes for Open Mobile Alliance (OMA) Broadcast (BCAST) Service and Content Protection", RFC 5159, March 2008.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", RFC 5245, July 2006.
[RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP Header Extensions", RFC 5285, July 2008.
[RFC5432] Polk, J., Dhesikan, S. and G. Camarillo, "Quality of Service (QoS) Mechanism Selection in the Session Description Protocol (SDP)", RFC 5432, March 2009.
[RFC5506] Johansson, I., "Support for Reduced-Size Real-Time Transport Control Protocol (RTCP): Opportunities and Consequences", RFC 5506, 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, May 2009.
[RFC5576] Lennox, J., Ott, J. and T. Schierl, "Source-Specific Media Attributes in the Session Description Protocol (SDP)", RFC 5576, June 2009.
[RFC5583] Schierl, T. and S. Wenger, "Signaling Media Decoding Dependency in the Session Description Protocol (SDP)", RFC 5583, 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, February 2010.
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and Control Packets on a Single Port", RFC 5761, April 2010.
[RFC5762] Perkins, C., "RTP and the Datagram Congestion Control Protocol (DCCP)", RFC 5762, 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, May 2010.
[RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description Protocol (SDP) Grouping Framework", RFC 5888, June 2010.
[RFC5939] Andreasen, F., "S Description Protocol (SDP) Capability Negotiation", RFC 5939, September 2010.
[RFC5956] Begen, A., "Forward Error Correction Grouping Semantics in the Session Description Protocol", RFC 5956, 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, January 2011.
[RFC6128] Begen, A., "RTP Control Protocol (RTCP) Port for Source-Specific Multicast (SSM) Sessions", RFC 6128, February 2011.
[RFC6189] Zimmermann, P., Johnston, A. and J. Callas, "ZRTP: Media Path Key Agreement for Unicast Secure RTP", RFC 6189, 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, April 2011.
[RFC6230] Boulton, C., Melanchuk, T. and S. McGlashan, "Media Control Channel Framework", RFC 6230, May 2011.
[RFC6236] Johansson, I. and K. Jung, "Negotiation of Generic Image Attributes in the Session Description Protocol (SDP)", RFC 6236, May 2011.
[RFC6284] Begen, A., Wing, D. and T. Van Caenegem, "Port Mapping between Unicast and Multicast RTP Sessions", RFC 6284, June 2011.
[RFC6285] Ver Steeg, B., Begen, A., Van Caenegem, T. and Z. Vax, "Unicast-Based Rapid Acquisition of Multicast RTP Sessions", RFC 6285, June 2011.
[RFC6364] Begen, A., "S Description Protocol Elements for the Forward Error Correction (FEC) Framework", RFC 6364, October 2011.
[RFC6642] Wu, Q., Xia, F. and R. Even, "RTP Control Protocol (RTCP) Extension for a Third-Party Loss Report", RFC 6642, 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, 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, August 2012.
[RFC6773] Phelan, T., Fairhurst, G. and C. Perkins, "DCCP-UDP: A Datagram Congestion Control Protocol UDP Encapsulation for NAT Traversal", RFC 6773, November 2012.
[RFC6787] Burnett, D. and S. Shanmugham, "Media Resource Control Protocol Version 2 (MRCPv2)", RFC 6787, November 2012.
[RFC6871] Gimlan, R., Evan, R. and F. Andreasen, Session Description Protocol (SDP) Media Capabilities Negotiation", RFC 6871, Febrauary 2013.
[RTCP-FB]S Description Protocol (SDP) RTCP Feedback attributes", .
[SSRC-GROUP]S Description Protocol (SDP) "ssrc-group" semantics", .
[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