Network Working Group S. Nandakumar
Internet-Draft Cisco
Intended status: Standards Track September 24, 2013
Expires: March 28, 2014

A Framework for SDP Attributes when Multiplexing
draft-nandakumar-mmusic-sdp-mux-attributes-04

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 Sessions 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 March 28, 2014.

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

Real-Time Communication Web (RTCWeb) framework requires Real-time Transport Protocol 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 RTCWeb WG, a requirement has arisen to multiplex several RTP Sessions over a single transport layer flow. 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-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 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.

     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

     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

     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

      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



     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 two,one
     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

With the above semantic grouping as the reference, 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.
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.
NOT RECOMMENDED
Attributes where multiplexing is not recommended if these attributes are in use in the SDP since doing so MAY result in incorrect behaviors
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.
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, there is no way to receive RTCP control data for the video m=line in the example below. Hence rtcp-mux MUST be repeated for the video m=line as well, when 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.
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.
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.
In the example below, "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" appears ahead of it in the SDP. This is due to BUNDLE grouping semantics [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.
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.
TBD
This category defines attributes that need more information to assign an appropriate category.

The idea behind these categories is to provide recommendations for using the attributes under RTP session multiplexing scenarios.

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 - 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 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 - 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 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 - 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 Current Category
rtcp-mux  RTCP muxing should be repeated across all the m=lines  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 Current Category
label  Not Impacted  M NORMAL 

5.5. RFC5432 - QoS Mechanism Selection in SDP

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  Since QOS mechanism are signaled per flow, multiplexing multiple m=lines has no impact on per m=line QOS mechanism.  B NORMAL 
qos-mech-recv  Since QOS mechanism are signaled per flow, multiplexing multiple m=lines has no impact on per m=line QOS mechanism.  B NORMAL 

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 Current Category
crypto  The multiplexing scheme MUST ensure unique SSRCs across all the media lines multiplexed. In that case, cryptographic keys corresponding to the underlying transport is used. TRANSPORT 
crypto  If the multiplexing scheme cannot ensure unique SSRCs across all the media lines, multiplexing MUST NOT be performed. NOT RECOMMENDED 

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 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  If RFC 6773 is not being used in addition to RFC 5762, 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.  NOT RECOMMENDED 

If RFC 6773 is being used in addition to RFC 5762 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 standardised 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) middleboxes without modification of those middleboxes

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

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 Current Category
rtcp-rsize  RTCP reduced size MUST be repeated across all the m=lines  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 Current Category
resource  Not Impacted  NORMAL 
channel  Not Impacted  NORMAL 
Not Impacted  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 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 - 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 Current 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 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 - 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 Current Category
ssrc  SSRCs repeated over multiple m=lines is forbidden if the m-lines are in the same RTP session.   M NOT RECOMMENDED 
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 NOT RECOMMENDED 
fmtp  Not Impacted  SR NORMAL 

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 Current Category
imageattr  Not Impacted  NORMAL 

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 Current Category
rams-updates  Not recommended   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 Current Category
cfw-id  Not Applicable  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 Current Category
fec-source-flow  Not Impacted  NORMAL 
fec-repair-flow  Not Impacted  NORMAL 
repair-window  Not Impacted  NORMAL 

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

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 Current Category
portmapping-req  Not recommended, if port mapping is required by the application  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 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 Impacted  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 Current Category
floorctrl  Not Impacted  NORMAL 
confid  Not Impacted  NORMAL 
userid  Not Impacted  NORMAL 
floorid  Not Impacted  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 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 - 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 Current 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 Current Category
rtcp-xr  The attribute MUST be reported across all m=lines multiplexed  B IDENTICAL 

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

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 Current Category
source-filter  he 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 Current 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 Current 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 Current Category
setup  Should be identical across all m=lines  B
connection  Should be identical across all m=lines  B

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 Current Category
bcastversion  S TBD 
stkmstream  B TBD 
SRTPAuthentication  M TBD 
SRTPROCTxRate  M TBD 

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 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 

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 Current Category
X-predecbufsize  Case1:Aggregate total when video m-lines are muxed Case2:Multiplexing with audio m=lines is invalid M NOT RECOMMENDED 
X-initpredecbufperiod  Case1:Aggregate total when video m-lines are muxed Case2:Multiplexing with audio m=lines is invalid M NOT RECOMMENDED 
X-initpostdecbufperiod  Case1:Aggregate total when video m-lines are muxed Case2:Multiplexing with audio m=lines is invalid M NOT RECOMMENDED 
X-decbyterate Case1:Aggregate total when video m-lines are muxed Case2:Multiplexing with audio m=lines is invalid M NOT RECOMMENDED 
3gpp-videopostdecbufsize  Case1:Aggregate total when video m-lines are muxed. Case2:Multiplexing with audio m=lines is invalid M NOT RECOMMENDED 
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 TBD 
alt-group  Complicates selection of alternate m=lines grouped with alt-group on mulitplexing  M TBD 
3GPP-Adaptation-Support  M TBD 
3GPP-QoE-Metricsn  B TBD 
3GPP-Asset-Informatio  B TBD 
mbms-mode  B TBD 
mbms-flowid  Multiplexing multiple m=lines complicates FEC mappings to the transport addresses.  M TBD 
mbms-repair  B TBD 

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 Current Category
aalType  TBD 
eecid  TBD 
aalType  TBD 
capability  TBD 
qosClass  TBD 
bcob  TBD 
stc  TBD 
upcc  TBD 
atmQOSparms  TBD 
atmTrfcDesc  TBD 
abrParms  TBD 
abrSetup  nbsp; TBD 
bearerType  TBD 
lij  TBD 
anycast  TBD 
cache  TBD 
bearerSigIE  TBD 
aalApp  TBD 
cbrRate  TBD 
sbc  TBD 
clkrec  TBD 
fec  TBD 
prtfl  TBD 
structure  TBD 
cpsSDUsize  TBD 
aal2CPS  TBD 
aal2CPSSDUrate  TBD 
aal2sscs3661unassured  TBD 
aal2sscs3661assured  TBD 
aal2sscs3662  TBD 
aal5sscop  TBD 
atmmap  TBD 
silenceSupp  TBD 
ecan  TBD 
gc  TBD 
profileDesc  TBD 
vsel  TBD 
dsel  TBD 
fsel  TBD 
onewaySel  TBD 
codecconfig  TBD 
isup_usi  TBD 
isup_usi  TBD 
chain  TBD 

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  Usage defined for the IP Multimedia Subsystem  M NORMAL 

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  Usage defined for the IP Multimedia Subsystem  M NORMAL 

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  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 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 

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 Current 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 Current Category
accept-types  Not Impacted  NORMAL 
accept-wrapped-types  Not Impacted  NORMAL 
max-size  Not Impacted  NORMAL 
path  Not Impacted  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 Current Category
rtpred1  Not Applicable  Not-Applcable TBD 
rtpred2  Not Applicable  Not-Applcable TBD 
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 Current Category
bwtype:CT  Aggregate bandwidth for the conference  S NORMAL 
bwtype:AS  There are 2 interpretations for this attribute 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 belongs to NORMAL category. For the media level usage, the aggregate of individual bandwidth values is considered.  B NORMAL, 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 Current 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 Current Category
bwtype:TIAS  The usage of TIAS is not clearly defined Offer/Answer usage.  B TBD 
maxprate  The usage of TIAS and maxprate is not well defined under multiplexing  B TBD 

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 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 - 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 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 - 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 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 - Unicast-Based RAMS

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

8.3. 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 initialisation method using Interactive Connectivity Establishment (ICE)

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

8.4. 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 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 - Codec Control Messages in AVPF

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 - 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 Current Category
group:LS  Not Impacted  NORMAL 
group:FID  Not Impacted  NORMAL 

10.2. 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 Current Category
group:SRF  Not Impacted  NORMAL 

10.3. 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 Current Category
group:ANAT  Not Impacted   NOT RECOMMENDED 

10.4. 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 Current Category
group:FEC-FR  Not Impacted  NORMAL 

10.5. 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 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 - Source-Specific SDP Attributes

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 - QoS Mechanism Selection in SDP

RFC5432 Attribute Analysis
Name Notes Current 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 

13. k= Attribute Analysis

13.1. RFC4566 SDP: Session Description Protocol

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

14. content Atribute Analysis

14.1. RFC4796 - MSRP Relays

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 - 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 Current 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 RECOMMEDED 
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 multipelxing and ULP is allowed when used with that.

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           |
+---------------------+
| 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 helping review the draft.

I would like also to thank following experts on their inputs and reviews as listed - Rohan Mahy(5.45), Eric Burger(5.22), Christian Huitema(5.13), Christer Holmberg(5.22,5.40,5.41), Richard Ejzak (5.42,5.43,5.44),Colin Perkins(5.7,5.8), Magnus westerlund(5.3,5.9,6.1,6.2,6.3,8.3), Subha Dhesikan(5.5,12.1), Dan Wing(5.6,5.34,5.37), Eric Rescorla (5.11), Ali C Begen(5.1,5.16,5.18,8.2,5.33,13.1)

19. Change Log

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

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

[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", .

Author's Address

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