Network Working Group S. Nandakumar
Internet-Draft C. Jennings
Intended status: Standards Track Cisco
Expires: August 28, 2013 February 24, 2013

A Framework for SDP Attributes when Multiplexing
draft-nandakumar-mmusic-sdp-mux-attributes-01

Abstract

Communication sessions in RTCWeb are described and negotiated using Session Description Protocol(SDP)[RFC4566] mechanisms. SDP uses attributes to describes specific aspects of such a session. These attributes have different impacts when using varions of multiplexing RTP on a single transport layer flow. The scope of this specification is to provide a framework for analyzing the multiplex characteristics for SDP attributes and provide multiplexing characteristics of existing attributes.

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 August 28, 2013.

Copyright Notice

Copyright (c) 2013 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[RFC4566] defines several attributes for describing specific aspects of a multimedia session. Given the number of SDP attributes registered with IANA [IANA]and the defining new attributes in the future, there is need for future-proof framework to analyze these attributes for their applicability in transport multiplexing use-cases. Few proposed schemes for the same are defined in [I-D.ietf-mmusic-sdp-bundle-negotiation] and [I-D.ietf-avt-multiplexing-rtp]

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 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 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-mline 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 180 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 multiplexing.

4. SDP Attribute Analysis Framework

An SDP session description consists of a session-level section followed by zero or more media-level sections that could be broken down into following high-level categories

The proposed framework classifies each attribute into one of the following categories:

NORMAL
Attributes that can be independently specified when multiplexing and retain their original semantics .
BAD
Attributes where multiplexing SHOULD NOT be used if these attributes are in use in the SDP.
IDENTICAL
Attributes that MUST be identical across all the media lines being multiplexed.
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.
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=" lines that represents the information being used for the transport of the RTP. Readers are advised to refer Section TRANSPORT_EXAMPLE [sec-transport] for an illustration of this category.
SPECIAL
Attributes where the text in the draft must be consulted to see how they are handled when multiplexing.

The idea behind these categories is to provide recommendations for using the attributes when multiplexing is being used.

Section 5 analyzes attributes listed in IANA [IANA] grouped under the IETF document that defines them. The "Current" column indicates whether the attribute is currently specified as:

5. Analysis of Existing Attributes

5.1. RFC4566

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 Current Category
sendrecv  Not impacted  NORMAL 
sendonly  Not impacted  NORMAL 
recvonly  Not impacted  NORMAL 
inactive  Not impacted  NORMAL 
cat  Not impacted  NORMAL 
ptime  Not Impacted   NORMAL
maxptime  Not Impacted   NORMAL
orient  Not Impacted   NORMAL
framerate  Not Impacted   NORMAL 
quality  Not Impacted   NORMAL
rtpmap  Not Impacted   NORMAL
fmtp  Not Impacted   NORMAL
keywds  Not impacted  NORMAL 
type  Not Impacted   NORMAL 
tool  Not Impacted   NORMAL 
charset  Not Impacted   NORMAL 
sdplang  Not Impacted   NORMAL 
lang  Not Impacted   NORMAL 

5.2. RFC4585

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 Current Category
rtcp-fb  Since RTCP feedback are reported per RTP Session,  this attribute should be repeated across m= lines M IDENTICAL 

5.3. RFC5761

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 Current Category
rtcp-mux  RTCP muxing should be repeated across all the m=lines  IDENTICAL 

5.4. RFC4574

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 Current Category
label  Not Impacted  M NORMAL 

5.5. RFC5432

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

RFC5432 Attribute Analysis
Name Notes Current Category
qos-mech-send  QOS mechanism should be same across all the m=lines multiplexed  B IDENTICAL 
qos-mech-recv  AQOS mechanism should be same across all the m=lines multiplexed  B IDENTICAL 

5.6. RFC4568

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 Current Category
crypto  TRANSPORT 

Open Isuse: should this be NORMAL

5.7. RFC5762

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 signalling, such that real-time applications can make use of the services provided by DCCP

RFC5762 Attribute Analysis
Name Notes Current Category
dccp-service-code  Not recommended due to DCCP service code mismatch between different media types  BAD 

5.8. RFC6773

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) middleboxes without modification of those middleboxes

RFC6773 Attribute Analysis
Name Notes Current Category
dccp-port  Not recommended due to DCCP service code mismatch between different media types  BAD 

5.9. RFC5506

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 Current Category
rtcp-rsize  RTCP reduced size MUST be repeated across all the m=lines  IDENTICAL 

5.10. RFC6787

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 Current Category
resource  Not Impacted  NORMAL 
channel  Not Impacted  NORMAL 
Not Impacted  NORMAL 

5.11. RFC5245

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 Current Category
ice-lite  Not Impacted  S NORMAL 
ice-options  Not Impacted  S NORMAL 
ice-options  Not Impacted  S NORMAL 
ice-pwd  Per media-level attribute MUST be used per underlying transport flow  B TRANSPORT 
ice-ufrag  Per media-level attribute MUST be used per underlying transport flow  B TRANSPORT 
candidate  Per media-level attribute MUST be used per underlying transport flow  TRANSPORT 
remote-candidates  Per media-level attribute MUST be used per underlying transport flow  M TRANSPORT 

5.12. RFC5285

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 Current Category
extmap  Specific RTP extension document MUST be referred  B SPECIAL 

5.13. RFC3605

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 Current Category
rtcp  Case1:Same RTCP port is repeated across the m=lines. Case2:Different RTCP ports renders multiplexing impossible  M TRANSPORT 

5.14. RFC5576

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 Current Category
ssrc  SSRCs repeated over multiple m=lines is forbidden if the m-lines are in the same RTP session.   M BAD 
ssrc-group  Refer to section Section 11 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  SSRCs repeated over multiple m=lines complicates multiplexing  SR BAD 
fmtp  Not Impacted  SR NORMAL 

5.15. RFC6236

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 Current Category
imageattr  Not Impacted  NORMAL 

5.16. RFC6285

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 Current Category
rams-updates  Not recommended   BAD 

5.17. RFC6230

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 Current Category
cfw-id  Not Applicable  NORMAL 

5.18. RFC6364

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 Current Category
fec-source-flow  Not Impacted  NORMAL 
fec-repair-flow  Not Impacted  NORMAL 
repair-window  Not Impacted  NORMAL 

5.19. RFC4796

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 Current Category
content  Not Impacted  NORMAL 

5.20. RFC3407

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 Current Category
sqn  Not Impacted  B NORMAL 
csdc  Mismatch in the offered capability description MAY fail multiplexing.  B BAD 
cpar  Mismatch in the offered capability parameters MAY fail multiplexing.  B BAD 
cparmin  Mismatch in the offered capability parameters MAY fail multiplexing.  B BAD 
cparmax  Mismatch in the offered capability parameters MAY fail multiplexing.  B BAD 

5.21. RFC6284

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 Current Category
portmapping-req  Not recommended, if port mapping is required by the application  BAD 

5.22. RFC6714

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

RFC6714 Attribute Analysis
Name Notes Current Category
msrp-cema  Not recommended due to legacy interop purposes  NORMAL 

5.23. RFC4583

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 Current Category
floorctrl  Not Impacted  NORMAL 
confid  Not Impacted  NORMAL 
userid  Not Impacted  NORMAL 
floorid  Not Impacted  NORMAL 

5.24. RFC5547

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 Current Category
file-selector  Not Impacted  M NORMAL 
file-transfer-id  Not Impacted  M NORMAL 
file-disposition  Not Impacted  M NORMAL 
file-date,file-iconfile-range  Not Impacted  M NORMAL 
file-iconfile-range  Not Impacted  M NORMAL 
file-iconfile-range  Not Impacted  M NORMAL 

5.25. draft-ietf-mmusic-media-loopback

[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.

draft-ietf-mmusic-media-loopback Attribute Analysis
Name Notes Current Category
loopback rtp-pkt-loopback  The attribute MUST be repeated across all m=lines multiplexed   M IDENTICAL 
loopback rtp-media-loopback  Not Impacted   M NORMAL 
loopback-source  Not Impacted  M NORMAL 
loopback-mirror  Not Impacted  M NORMAL 

5.26. RFC5760

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 Current Category
rtcp-unicast  The attribute MUST be reported across all m=lines multiplexed  M IDENTICAL 

5.27. RFC3611

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 Current Category
rtcp-xr  The attribute MUST be reported across all m=lines multiplexed  B IDENTICAL 

5.28. RFC5939

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 Current Category
pcfg  Depends on capability being negotiated   M SPECIAL 
acfg  Depends on capability being negotiated   M SPECIAL 
csup  Depends on capability being negotiated  B SPECIAL 
creq  Depends on capability being negotiateds  B SPECIAL 
acap  Depends on capability being negotiated  B SPECIAL 
tcap  Repeat transport capability across all m= lines  B IDENTICAL 

5.29. draft-ietf-mmusic-sdp-media-capabilities

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. [MEDIA_CAP] extends the framework by defining media capabilities that can be used to negotiate media types and their associated parameters.

draft-ietf-mmusic-sdp-media-capabilities Attribute Analysis
Name Notes Current Category
rmcap  Not Impacted  B NORMAL 
omcap  Not Impacted  B NORMAL 
mfcap  Not Impacted  B NORMAL 
mscap  Not Impacted  B NORMAL 
lcfg  Not Impacted  B NORMAL 
secap  Not Impacted  S NORMAL 

5.30. RFC4567

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 Current Category
key-mgmt  Key management protocol MUST be identical across all the m=lines  B IDENTICAL 

5.31. RFC4572

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 Current Category
fingerprint  Fingerprint value MUST be identical across all the m=lines  B IDENTICAL 

5.32. RFC4570

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 Current Category
source-filter  he attribute MUST be repeated across all m=lines multiplexed  B IDENTICAL 

5.33. RFC6128

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 Current Category
multicast-rtcp  Multicast RTCP port MUST be identical across all the m=lines  B IDENTICAL 

5.34. RFC6189

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 Current Category
zrtp-hash  Complicates if all the m=lines are not authenticated  M BAD 

5.35. RFC4145

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 Current Category
setup  Not recommended for multiplexing due to possible differences in the protocol and media types  B BAD 
connection  Not recommended for multiplexing due to possible differences in the protocol and media types  B BAD 

5.36. RFC5159

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 Current Category
bcastversion  Not recommended for multiplexing for legacy interop purposes  S BAD 
stkmstream  Not recommended for multiplexing for legacy interop purposes  B BAD 
SRTPAuthentication  Not recommended for multiplexing for legacy interop purposes  M BAD 
SRTPROCTxRate  Not recommended for multiplexing for legacy interop purposes  M BAD 

5.37. RFC6193

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 Current 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 

In the case of session multiplexed with multiple m=lines, this SHOULD create only one IPSEC association for all the m=lines.

5.38. RFC6064

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 Current Category
X-predecbufsize  Case1:Aggregate total when video m-lines are muxed Case2:Multiplexing with audio m=lines is invalid M BAD 
X-initpredecbufperiod  Case1:Aggregate total when video m-lines are muxed Case2:Multiplexing with audio m=lines is invalid M BAD 
X-initpostdecbufperiod  Case1:Aggregate total when video m-lines are muxed Case2:Multiplexing with audio m=lines is invalid M BAD 
X-decbyterate Case1:Aggregate total when video m-lines are muxed Case2:Multiplexing with audio m=lines is invalid M BAD 
3gpp-videopostdecbufsize  Case1:Aggregate total when video m-lines are muxed. Case2:Multiplexing with audio m=lines is invalid M BAD 
framesize Not Impacted M NORMAL 
3GPP-Integrity-Key  Not Impacted S NORMAL 
3GPP-SRTP-Config  Same config SHALL apply to all the m=lines multiplexed  M NORMAL 
alt,alt-default-id  Specifying alternate m=lines when session with mulitple m=lines of different types cannot be clearly specified  M BAD 
alt-group  Complicates selection of alternate m=lines grouped with alt-group on mulitplexing  M BAD 
3GPP-Adaptation-Support  Not recommended for legacy interop purposes  M BAD 
3GPP-QoE-Metricsn  Not recommended for legacy interop purposes  B BAD 
3GPP-Asset-Informatio  Not recommended for legacy interop purposes  B BAD 
mbms-mode  Not recommended for legacy interop purposes  B BAD 
mbms-flowid  Multiplexing multiple m=lines complicates FEC mappings to the transport addresses.  M BAD 
mbms-repair  Not recommended for legacy interop purposes  B BAD 

5.39. RFC3108

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 Current Category
aalType  Not recommended for legacy interop purposes  BAD 
eecid  Not recommended for legacy interop purposes  BAD 
aalType  Not recommended for legacy interop purposes  BAD 
capability  Not recommended for legacy interop purposes  BAD 
qosClass  Not recommended for legacy interop purposes  BAD 
bcob  Not recommended for legacy interop purposes  BAD 
stc  Not recommended for legacy interop purposes  BAD 
upcc  Not recommended for legacy interop purposes  BAD 
atmQOSparms  Not recommended for legacy interop purposes  BAD 
atmTrfcDesc  Not recommended for legacy interop purposes  BAD 
abrParms  Not recommended for legacy interop purposes  BAD 
abrSetup  Not recommended for legacy interop purposes  BAD 
bearerType  Not recommended for legacy interop purposes  BAD 
lij  Not recommended for legacy interop purposes  BAD 
anycast  Not recommended for legacy interop purposes  BAD 
cache  Not recommended for legacy interop purposes  BAD 
bearerSigIE  Not recommended for legacy interop purposes  BAD 
aalApp  Not recommended for legacy interop purposes  BAD 
cbrRate  Not recommended for legacy interop purposes  BAD 
sbc  Not recommended for legacy interop purposes  BAD 
clkrec  Not recommended for legacy interop purposes  BAD 
fec  Not recommended for legacy interop purposes  BAD 
prtfl  Not recommended for legacy interop purposes  BAD 
structure  Not recommended for legacy interop purposes  BAD 
cpsSDUsize  Not recommended for legacy interop purposes  BAD 
aal2CPS  Not recommended for legacy interop purposes  BAD 
aal2CPSSDUrate  Not recommended for legacy interop purposes  BAD 
aal2sscs3661unassured  Not recommended for legacy interop purposes  BAD 
aal2sscs3661assured  Not recommended for legacy interop purposes  BAD 
aal2sscs3662  Not recommended for legacy interop purposes  BAD 
aal5sscop  Not recommended for legacy interop purposes  BAD 
atmmap  Not recommended for legacy interop purposes  BAD 
silenceSupp  Not recommended for legacy interop purposes  BAD 
ecan  Not recommended for legacy interop purposes  BAD 
gc  Not recommended for legacy interop purposes  BAD 
profileDesc  Not recommended for legacy interop purposes  BAD 
vsel  Not recommended for legacy interop purposes  BAD 
dsel  Not recommended for legacy interop purposes  BAD 
fsel  Not recommended for legacy interop purposes  BAD 
onewaySel  Not recommended for legacy interop purposes  BAD 
codecconfig  Not recommended for legacy interop purposes  BAD 
isup_usi  Not recommended for legacy interop purposes  BAD 
isup_usi  Not recommended for legacy interop purposes  BAD 
chain  Not recommended for legacy interop purposes  BAD 

5.40. 3GPP TS 24.182

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

3GPP TS 24.182 Attribute Analysis
Name Notes Current Category
g.3gpp.cat  Not recommended due to interop purposes  M BAD 

5.41. 3GPP TS 24.183

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

3GPP TS 24.183 Attribute Analysis
Name Notes Current Category
g.3gpp.crs  Not recommended due to interop purposes  M BAD 

5.42. 3GPP TS 24.229

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

3GPP TS 24.229 Attribute Analysis
Name Notes Current Category
secondary-realm  Not recommended due to interop purposes  M BAD 
visited realm  Not recommended due to interop purposes  M BAD 
omr-m-cksum  Not recommended due to interop purposes  M BAD 
omr-s-cksum  Not recommended due to interop purposes  M BAD 
omr-m-att  Not recommended due to interop purposes  M BAD 
omr-s-att  Not recommended due to interop purposes  M BAD 
omr-s-bw  Not recommended due to interop purposes  M BAD 
omr-m-att  Not recommended due to interop purposes  M BAD 
omr-codecs  Not recommended due to interop purposes  M BAD 

5.43. ITU T.38

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

Historic Attribute Analysis
Name Notes Current 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 

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 Current Category
h248item  Not recommended for interop purposes  S BAD 

5.45. RFC4975

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 Current Category
accept-types  Not recommended due to incompatible media types  BAD 
accept-wrapped-types  Not recommended due to incompatible media typess  BAD 
max-size  Not recommended due to incompatible media types  BAD 
path  Not recommended due to incompatible media types  BAD 

5.46. Unknowns

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

Unknowns Attribute Analysis
Name Notes Current Category
rtpred1  Not Applicable  Not-Applcable BAD 
rtpred2  Not Applicable  Not-Applcable BAD 
PSCid  Not Applicable  Not-Applcable BAD 
bc_service  Not Applicable  Not-Applcable BAD 
bc_program  Not Applicable  Not-Applcable BAD 
bc_service_package  Not Applicable  Not-Applcable BAD 

6. bwtype Attribute Analysis

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

6.1. RFC4566

RFC4566 bwtype Analysis
Name Notes Current Category
bwtype:CT  Aggregate bandwidth for the conference  S NORMAL 
bwtype:AS  Aggregate RTP session bandwidth  B NORMAL,SUM 

6.2. RFC3556

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 Current Category
bwtype:RS  B NORMAL,SUM;
bwtype:RR  B NORMAL,SUM 

6.3. RFC3890

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 Current Category
bwtype:TIAS  Application MUST SUM bandwidth from all m=lines of same type and MUST NOT use default values  B SUM 

7. rtcp-fb Attribute Analysis

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

7.1. RFC4585

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 Current Category
ack  Not Impacted M NORMAL 
app  Not Impacted M NORMAL 
nack  Not Impacted M NORMAL 
trr-int  Not Impacted M NORMAL 

7.2. RFC5104

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 Current Category
ccm  Not Impacted M Normal 

8. rtcp-fb "ack/nack" Attribute Analysis

This section analyzes rtcp-fb SDP attributes specific to ack and nack feedback types [ACK-NACK].

8.1. RFC4585

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 Current Category
nack sli  Not Impacted M NORMAL 
nack pli  Not Impacted M NORMAL 
ack rpsi  Not Impacted M NORMAL 
ack app  Feedback parameters MUST be handled in the app specifc way when multiplexed M SPECIAL 
nack rpsi  Not Impacted M NORMAL 
nack app  Feedback parameters MUST be handled in the app specifc way when multiplexed M SPECIAL 

8.2. RFC6285

RFC6285 Attribute Analysis
Name Notes Current Category
nack rai  Not Impacted  NORMAL 

8.3. RFC6679

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 initialisation method using Interactive Connectivity Establishment (ICE)

RFC6679 Attribute Analysis
Name Notes Current Category
nack ecn  Complicates ECN marking when m=lines of different types are used  SPECIAL 

8.4. RFC6642

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 Current Category
tllei  Not Impacted  NORMAL 
pslei  Not Impacted  NORMAL 

9. Codec Control Messages Analysis

This section analyzes rtcp-fb Codec Control Message [CCM].

9.1. RFC5104

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

10. group Attribute Analysis

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

10.1. RFC5888

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

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

10.2. RFC3524

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 Current Category
group:SRF  Not Impacted  NORMAL 

10.3. RFC4091

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 Current Category
group:ANAT  Not Impacted   BAD 

10.4. RFC5956

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 Current Category
group:FEC-FR  Not Impacted  NORMAL 

10.5. RFC5583

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 Current Category
depend lay  Not Impacted  M NORMAL 
depend mdc  Not Impacted  M NORMAL 

11. ssrc-group Attribute Analysis

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

11.1. RFC5576

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

12. QoS Mechanism Token Analysis

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

12.1. RFC5432

RFC5432 Attribute Analysis
Name Notes Current Category
rsvp  Not Impacted  B NORMAL 
nsis  Not Impacted  B NORMAL 

13. k= Attribute Analysis

13.1. RFC4566

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

14. content Atribute Analysis

14.1. RFC4796

RFC4796 Attribute Analysis
Name Notes Current 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 

15. Payload Formats

15.1. RFC5109

RFC4145 [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 Current Category
audio/ulpfec  Not recommended for multiplexing due to reuse of SSRCs  M BAD 
video/ulpfec  Not recommended for multiplexing due to reuse of SSRCs  M BAD 
text/ulpfec  Not recommended for multiplexing due to reuse of SSRCs  M BAD 
application/ulpfec  Not recommended for multiplexing due to reuse of SSRCs  M BAD 

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

16. TRANSPORT Category Example

The example below explains the usage of "TRANSPORT" category for RFC4586 "crypto" parameter when SDP Port number based multiplexing is performed for audio and video streams.



     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 second,first
     m=audio 49172 RTP/AVP 99
     a=mid:one
     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:two
     a=crypto:1 AES_CM_128_HMAC_SHA1_80
       inline:EcGZiNWpFJhQXdspcl1ekcmVCNWpVLcfHAwJSoj|2^20|1:32
     a=rtpmap:96 H261/90000    

In this example, "a=crypto" attribute is defined for both the audio and the video m=lines.The one that MUST be used for the multiplexed RTP Session is the one that corresponds to m=line with mid "two" even though the audio m=line with mid "one" occurs ahead of it. This is due to BUNDLE grouping semantics [I-D.ietf-mmusic-sdp-bundle-negotiation] which mandates the values from mid occuring first on the a=group:BUNDLE line to be considered for seting up the RTP Transport.

17. IANA Considerations

TBD

Future versions of this specification will ask the IANA to expand to attribute tables to include an extra column specifying categories from this draft.

18. Security Considerations

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

19. Change Log

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

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

20. References

20.1. Normative References

[RFC4566] Handley, M., Jacobson, V. and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

20.2. Informative References

, ", ", ", ", ", ", ", ", ", ", ", "
[RFC5109] Li, A., "RTP Payload Format for Generic Forward Error Correction", RFC 5109, December 2007.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002.
[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.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", RFC 5245, July 2006.
[RFC5506] Johansson, I., "Support for Reduced-Size Real-Time Transport Control Protocol (RTCP): Opportunities and Consequences", RFC 5506, April 2009.
[RFC4796] Hautakorpi, J. and G. Camarillo, "The Session Description Protocol (SDP) Content Attribute", RFC 4796, February 2007.
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and Control Packets on a Single Port", RFC 5761, April 2010.
[RFC3556] Casner, S., "Session Description Protocol (SDP) Bandwidth Modifiers for RTP Control Protocol (RTCP) Bandwidth", RFC 3556, July 2003.
[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.
[RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description Protocol (SDP) Grouping Framework", RFC 5888, June 2010.
[RFC4574] Levin, O. and G. Camarillo, "The Session Description Protocol (SDP) Label Attribute", RFC 4574, August 2006.
[RFC5432] Polk, J., Dhesikan, S. and G. Camarillo, "Quality of Service (QoS) Mechanism Selection in the Session Description Protocol (SDP)", RFC 5432, March 2009.
[RFC4568] Andreasen, F., Baugher, M. and D. Wing, "Session Description Protocol (SDP) Security Descriptions for Media Streams", RFC 4568, July 2006.
[RFC5762] Perkins, C., "RTP and the Datagram Congestion Control Protocol (DCCP)", RFC 5762, April 2010.
[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.
[RFC3890] Westerlund, M., "A Transport Independent Bandwidth Modifier for the Session Description Protocol (SDP)", RFC 3890, September 2004.
[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP)", RFC 3605, October 2003.
[RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP Header Extensions", RFC 5285, July 2008.
[RFC5576] Lennox, J., Ott, J. and T. Schierl, "Source-Specific Media Attributes in the Session Description Protocol (SDP)", RFC 5576, June 2009.
[RFC6236] Johansson, I. and K. Jung, "Negotiation of Generic Image Attributes in the Session Description Protocol (SDP)", RFC 6236, May 2011.
[RFC5583] Schierl, T. and S. Wenger, "Signaling Media Decoding Dependency in the Session Description Protocol (SDP)", RFC 5583, July 2009.
[RFC6285] Ver Steeg, B., Begen, A., Van Caenegem, T. and Z. Vax, "Unicast-Based Rapid Acquisition of Multicast RTP Sessions", RFC 6285, June 2011.
[RFC6230] Boulton, C., Melanchuk, T. and S. McGlashan, "Media Control Channel Framework", RFC 6230, May 2011.
[RFC6364] Begen, A., "Session Description Protocol Elements for the Forward Error Correction (FEC) Framework", RFC 6364, October 2011.
[RFC3407] Andreasen, F., "Session Description Protocol (SDP) Simple Capability Declaration", RFC 3407, October 2002.
[RFC6284] Begen, A., Wing, D. and T. Van Caenegem, "Port Mapping between Unicast and Multicast RTP Sessions", RFC 6284, June 2011.
[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.
[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.
[RFC4583] Camarillo, G., "Session Description Protocol (SDP) Format for Binary Floor Control Protocol (BFCP) Streams", RFC 4583, November 2006.
[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.
[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.
[RFC3611] Friedman, T., Caceres, R. and A. Clark, "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, November 2003.
[RFC5939] Andreasen, F., "Session Description Protocol (SDP) Capability Negotiation", RFC 5939, September 2010.
[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.
[RFC4572] Lennox, J., "Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP)", RFC 4572, July 2006.
[RFC4570] Quinn, B. and R. Finlayson, "Session Description Protocol (SDP) Source Filters", RFC 4570, July 2006.
[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.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the Session Description Protocol (SDP)", RFC 4145, September 2005.
[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.
[RFC6642] Wu, Q., Xia, F. and R. Even, "RTP Control Protocol (RTCP) Extension for a Third-Party Loss Report", RFC 6642, June 2012.
[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.
[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.
[RFC5956] Begen, A., "Forward Error Correction Grouping Semantics in the Session Description Protocol", RFC 5956, September 2010.
[RFC3108] Kumar, R. and M. Mostafa, "Conventions for the use of the Session Description Protocol (SDP) for ATM Bearer Connections", RFC 3108, May 2001.
[RFC5159] Dondeti, L. and A. Jerichow, "Session Description Protocol (SDP) Attributes for Open Mobile Alliance (OMA) Broadcast (BCAST) Service and Content Protection", RFC 5159, March 2008.
[RFC3524] Camarillo, G. and A. Monrad, "Mapping of Media Streams to Resource Reservation Flows", RFC 3524, April 2003.
[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.
[RFC4975] Campbell, B., Mahy, R. and C. Jennings, "The Message Session Relay Protocol (MSRP)", RFC 4975, September 2007.
[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 draft-ietf-mmusic-media-loopback-27, January 2013.
[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.
[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.
[MEDIA_CAP] Kaplan, H., Hedayat, K. and N. Venna, "Session Description Protocol (SDP) Media Capabilities Negotiation", Internet-Draft draft-ietf-mmusic-sdp-media-capabilities-17, January 2013.
[IANA]Session Description Protocol (SDP) Parameters", .
[T.38]Procedures for real-time Group 3 facsimile communication over IP networks", .
[H.248.15]Gateway control protocol: SDP H.248 package attribute", .
[3GPP TS 24.229]IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP);", .
[3GPP TS 24.182]IP Multimedia Subsystem (IMS) Customized Alerting Tones (CAT); Protocol specification", .
[3GPP TS 24.183]IP Multimedia Subsystem (IMS) Customized Ringing Signal (CRS); Protocol specification", .
[RTCP-FB]Session Description Protocol (SDP) RTCP Feedback attributes", .
[ACK-NACK]Session Description Protocol (SDP) RTCP ACK/NACK Feedback attributes", .
[CCM]Session Description Protocol (SDP) RTCP-FB Codec Control Messages", .
[GROUP-SEM]Session Description Protocol (SDP) "group" semantics", .
[SSRC-GROUP]Session Description Protocol (SDP) "ssrc-group" semantics", .
[QOS]Session Description Protocol (SDP) QoS Mechanism Tokens", .

Authors' Addresses

Suhas Nandakumar Cisco 170 West Tasman Drive San Jose, CA 95134 USA EMail: snandaku@cisco.com
Cullen Jennings Cisco 400 3rd Avenue SW, Suite 350 Calgary, AB T2P 4H2 Canada EMail: fluffy@iii.ca