A Framework for SDP Attributes when Multiplexing

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 defines a way to use a single address:port combination (BUNDLE address) for receiving media associated with multiple SDP media descriptions. This would for e.g. allow the usage of a single set of ICE candidates for multiple media descriptions. This in turn has made necessary to understand the interpretation and usage of the SDP attributes defined for the multiplexed media descriptions. Given the number of SDP attributes registered with the 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 apply the framework to the SDP attributes registered with the .

5-tuple: A collection of the following values: source address, source port, destination address, destination port, and transport-layer protocol. The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in .

The time and complications of setting up ICE and DTLS-SRTP transports for use by RTP, and conservation of ports (to avoid maintaining large number of NAT bindings open, reduce time/ports needed for ICE to detect connectivity), forms a requirement to try and reduce the number of transport level flows needed. This has resulted in the definition of ways, such as, to multiplex RTP over a single transport flow in order to preserve network resources such as port numbers. This imposes further restrictions on applicability of the SDP attributes as they are defined today. The specific problem is that there are attribute combinations which make sense when specified on independent "m=" lines -- as with classical SDP -- that do not make sense when those "m=" lines are then multiplexed over the same transport. To give an obvious example, ICE permits each "m=" line to have an independently specified ice-ufrag attribute. However, if the media from multiple "m=" lines is multiplexed over the same ICE component, then the meaning of media-level ice-ufrag attributes becomes muddled. At the time of writing this document there are close to 250 SDP attributes registered with the and more will be added in the future. There is no clearly defined procedure to establish the validity/applicability of these attributes when used with transport multiplexing.

Attributes in an SDP session description can be defined at the session-level and media-level. Informally, these attributes could be semantically grouped as noted below. Attributes related to media content such as media type, encoding schemes, payload types. Attributes specifying media transport characteristics like RTP/RTCP port numbers, network addresses, QOS. Metadata description attributes capturing session timing and origin information. Attributes establishing relationships between media descriptions such as grouping framework With the above semantic grouping as a reference, the proposed framework classifies each attribute into one of the following categories:

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.

Attributes that are not recommended for multiplexing since their usage under multiplexing might lead to incorrect behavior. Example: Multiplexing media descriptions over a single DCCP transport is NOT RECOMMENDED since DCCP being a connection oriented protocol doesn't allow multiple connections on the same 5-tuple.

Attributes and their associated values (if any) that MUST be identical across all the media descriptions being multiplexed. Attributes such as rtcp-mux fall into this category. Since RTCP reporting is done per RTP session, RTCP Multiplexing MUST be enabled for both the audio and video "m=" lines if they are transported over a single 5-tuple.

Attributes can be set as they are normally used but software using them in the multiplexing scenario, MUST apply the sum of all the attributes being multiplexed instead of trying to use them independently. This is typically used for bandwidth or other rate limiting attributes to the underlying transport. The software parsing the SDP sample below, should use the aggregate Application Specific (AS) bandwidth value from the individual media descriptions to determine the AS value for the multiplexed session. Thus the calculated AS value would be 256+64 kilobits per second for the given example.

Attributes that can be set normally for multiple items in a multiplexed group but the software MUST pick the one that's associated with the "m=" line whose information is used for setting up the underlying transport. In the example below, "a=crypto" attribute is defined for both the audio and the video "m=" lines. The video media line's a=crypto attribute is chosen since its mid value (bar) appears first in the a=group:BUNDLE line. This is due to BUNDLE grouping semantic 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.

Attributes that encapsulate other SDP attributes or parameters. These attributes inherit their multiplexing characteristics from the attributes or parameters they encapsulate. Such attributes are defined in , and as part of a generic framework for indicating and negotiating transport, media and media format related capabilities in the SDP. The inheritance manifests itself when the encapsulated attribute or parameter is being leveraged. In the case of SDP Capability Negotiation for example, this occurs when a capability (encapsulating attribute) is used as part of a configuration; the configuration inherits the multiplexing category of each of its constituent (encapsulated) attributes and parameters. This in turn MAY place constraints on what constitutes a valid configuration from a multiplexing point of view, e.g. because some attributes MUST be IDENTICAL (see for further details).

In the above example, the category IDENTICAL is inherited for the cpar encapsulated rtcp-mux attribute.

Attributes that define the RTP payload configuration on per Payload Type basis and MUST have identical values across all the media descriptions for a given RTP Payload Type when repeated. These Payload Types identify the same codec configuration as defined in the Section 10.1.2 of under this context. In the SDP example below, Payload Types 96 and 97 are repeated across all the video "m=" lines and all the payload specific parameters (ex: rtpmap, fmtp) are identical (Note: some line breaks included are due to formatting only).

Attributes where the text in the specification defining the attribute MUST be consulted for further handling when multiplexed. As an example, for the attribute extmap , the specification defining the extension needs to be referred to understand the multiplexing implications.

Attributes that have not been analyzed under the proposed multiplexing framework. For the purposes of implementations it is advised to consider "NOT RECOMMENDED" as the category when multiplexing these attributes.

This section analyzes attributes listed in , grouped under the IETF document that defines them. The "Level" column indicates whether the attribute is currently specified as: S -- Session level M -- Media level B -- Both SR -- Source-level (for a single SSRC) The "Mux Category" column identifies multiplexing category assigned per attribute and the "Notes" column captures additional informative details regarding the assigned category, wherever necessary.

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

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. Name Notes Level Mux Category rtcp-mux RTP and RTCP Multiplexing affects the entire RTP session M IDENTICAL

defines a generic framework for preconditions, which are extensible through IANA registration. This document also discusses how network quality of service can be made a precondition for establishment of sessions initiated by the Session Initiation Protocol (SIP). These preconditions require that the participant reserve network resources before continuing with the session. Name Notes Level Mux Category des Refer to notes below M NOT RECOMMENDED conf Refer to notes below M NOT RECOMMENDED curr Refer to notes below M NOT RECOMMENDED NOTE: A mismatched set of preconditions across media descriptions results in Session establishment failures due to inability in meeting the right resource reservations requested.

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. Name Notes Level Mux Category label Not Impacted MNORMAL

defines procedures to negotiate QOS mechanisms using the Session Description Protocol (SDP) offer/answer model. Name Notes Level Mux Category qos-mech-send Refer to section BTRANSPORT qos-mech-recv Refer to section BTRANSPORT

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

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. specifies a mapping of RTP onto DCCP, along with associated signaling, such that real-time applications can make use of the services provided by DCCP. Name Notes Current Mux Category dccp-service-code If RFC6773 is not being used in addition to RFC5762, the port in the "m=" line is a DCCP port. DCCP being a connection oriented protocol, it does not allow multiple connections on the same 5-tuple M NOT RECOMMENDED If RFC6773 is being used in addition to RFC5762 and provided that DCCP-in-UDP layer has additional demultiplexing, then it may be possible to use different DCCP service codes for each DCCP flow, given each uses a different DCCP port. Although doing so might conflict with the media type of the "m=" line. None of this is standardized yet and it wouldn't work as explained. Hence multiplexing MUST not be performed even in this alternate scenario.

document specifies an alternative encapsulation of the Datagram Congestion Control Protocol (DCCP), referred to as DCCP-UDP. This encapsulation allows DCCP to be carried through the current generation of Network Address Translation (NAT) middle boxes without modification of those middle boxes. Name Notes Level Mux Category dccp-port Multiplexing MUST not be performed due to potential conflict between the port used for DCCP en/decapsulation and the RTP M NOT RECOMMENDED NOTE: RFC6773 is about tunneling DCCP in UDP, with the UDP port being the port of the DCCP en-/de-capsulation service. This encapsulation allows arbitrary DCCP packets to be encapsulated and the DCCP port chosen MAY conflict with the port chosen for the RTP traffic. For multiplexing several DCCP-in-UDP encapsulations on the same UDP port, with no RTP traffic on the same port implies collapsing several DCCP port spaces together. This may or may not work depending on the nature of DCCP encapsulation and ports choices thus rendering it to be very application dependent.

discusses benefits and issues that arise when allowing Real-time Transport Protocol (RTCP) packets to be transmitted with reduced size. Name Notes Level Mux Category rtcp-rsize Reduced size RTCP affects the entire RTP session M IDENTICAL

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. defines attributes for this purpose. Name Notes Level Mux Category resource Not Impacted M NORMAL channel Not Impacted M NORMAL cmid Not Impacted M NORMAL

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). Name Notes Level Mux Category ice-lite Not Impacted SNORMAL ice-options Not Impacted SNORMAL ice-mismatch Not Impacted SNORMAL ice-pwd ice-pwd MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow BTRANSPORT ice-ufrag ice-ufrag MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow BTRANSPORT candidate ice candidate MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow MTRANSPORT remote-candidates ice remote candidate MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow MTRANSPORT

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. Name Notes Level Mux Category extmap Specific RTP extension document MUST be referred BSPECIAL

Originally, SDP assumed that RTP and RTCP were carried on consecutive ports. However, this is not always true when NATs are involved. specifies an early mechanism to indicate the RTCP port. Name Notes Level Mux Category rtcp RTCP Port MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow. MTRANSPORT

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. Name Notes Level Mux Category ssrc Refer to Notes below MNORMAL ssrc-group Refer to for specific analysis of the grouping semantics M NORMAL cname Not Impacted SR NORMAL previous-ssrc Refer to notes below SRNORMAL fmtp The attribute value MUST be same for a given codec configuration SR IDENTICAL-PER-PT NOTE: If SSRCs are repeated across "m=" lines being multiplexed, they MUST all represent the same underlying RTP Source.

specifies Session Description Protocol (SDP) signalling that identifies timestamp reference clock sources and SDP signalling that identifies the media clock sources in a multimedia session. Name Notes Level Mux Category ts-refclk Not Impacted BNORMAL mediaclk Not Impacted BNORMAL

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. Name Notes Level Mux Category imageattr The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT

defines an attribute to indicate the presence of temporally redundant media streams and the duplication delay in the Session Description Protocol. Name Notes Level Mux Category duplication-delay Not Impacted B NORMAL

defines an RTP Control Protocol (RTCP) Extended Report (XR) Block including two new segment types and associated Session Description Protocol (SDP) parameters that allow the reporting of mean opinion score (MOS) Metrics for use in a range of RTP applications. Name Notes Level Mux Category calgextmap Not Impacted B NORMAL

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. Name Notes Level Mux Category rams-updates Not recommended M NOT RECOMMENDED

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. Name Notes Level Mux Category cfw-id Not Impacted M NORMAL

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. Name Notes Level Mux Category fec-source-flow Specific FEC scheme document needs to be referred M SPECIAL fec-repair-flow Specific FEC scheme document needs to be referred M SPECIAL repair-window Specific FEC scheme document needs to be referred M SPECIAL

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. Name Notes Level Mux Category content Not Impacted M NORMAL

defines a set of Session Description Protocol (SDP) attributes that enables SDP to provide a minimal and backwards compatible capability declaration mechanism. Name Notes Level Mux Category sqn Not Impacted BNORMAL cdsc Not Impacted. BNORMAL cpar Refer to BINHERIT cparmin Refer to notes below BSPECIAL cparmax Refer to notes below BSPECIAL NOTE: Since the attributes (a=cparmin and a=cparmax) define minimum and maximum numerical values associated with the attributes described in a=cpar, it is recommended to consult the document defining the attribute.

presents a port mapping solution that allows RTP receivers to choose their own ports for an auxiliary unicast session in RTP applications using both unicast and multicast services. The solution provides protection against denial-of-service or packet amplification attacks that could be used to cause one or more RTP packets to be sent to a victim client. Name Notes Level Mux Category portmapping-req Not recommended, if port mapping is required by the application M NOT RECOMMENDED

defines a Message Session Relay Protocol (MSRP) extension, Connection Establishment for Media Anchoring (CEMA). Support of this extension is OPTIONAL. The extension allows middle boxes to anchor the MSRP connection, without the need for middle boxes to modify the MSRP messages; thus, it also enables secure end-to-end MSRP communication in networks where such middle boxes are deployed. This document also defines a Session Description Protocol (SDP) attribute, 'msrp-cema', that MSRP endpoints use to indicate support of the CEMA extension. Name Notes Level Mux Category msrp-cema Refer to notes below M TBD NOTE: As per section 9.1 of , there exists no publicly available specification that defines procedures for multiplexing/demultiplexing MRSP flows over a single 5-tuple. Once such a specification is available, the multiplexing categories assignments for the attributes in this section MUST be revisited.

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. Name Notes Level Mux Category floorctrl The attribute MUST be repeated across all the multiplexed "m=" lines M IDENTICAL confid Not Impacted M NORMAL userid Not Impacted M NORMAL floorid The floorid MUST be globally unique M NORMAL

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 . Name Notes Level Mux Category file-selector Refer to notes below MTBD file-transfer-id Refer to notes below MTBD file-disposition Refer to notes below MTBD file-date Refer to notes below MTBD file-icon Refer to notes below MTBD file-range Refer to notes below MTBD NOTE: As per section 9.1 of , there exists no publicly available specification that defines procedures for multiplexing/demultiplexing MRSP flows over a single 5-tuple. Once such a specification is available, the multiplexing categories assignments for attributes in this section MUST be revisited.

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

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. Name Notes Level Mux Category rtcp-unicast The attribute MUST be reported across all "m=" lines multiplexed MIDENTICAL

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). Name Notes Level Mux Category rtcp-xr Not Impacted BNORMAL

defines a general SDP Capability Negotiation framework. It also specifies how to provide attributes and transport protocols as capabilities and negotiate them using the framework. Extensions for other types of capabilities (e.g., media types and media formats) may be provided in other documents. Name Notes Level Mux Category pcfg Refer to MSPECIAL acfg Refer to MSPECIAL csup Not Impacted B NORMAL creq Not Impacted B NORMAL acap Refer to BINHERIT tcap Refer to BINHERIT cap-v0 Not Impacted BNORMAL

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. extends the framework by defining media capabilities that can be used to negotiate media types and their associated parameters. Name Notes Level Mux Category rmcap Refer to BIDENTICAL-PER-PT omcap Not Impacted BNORMAL mfcap Refer to BIDENTICAL-PER-PT mscap Refer to BINHERIT lcfg Refer to BSPECIAL sescap Refer to notes below SNOT RECOMMENDED med-v0 Not Impacted SNORMAL NOTE: The "sescap" attribute is NOT RECOMMENDED for use with multiplexing. The reason is that it requires the use of unique configuration numbers across the entire SDP (per ) as opposed to within a media description only (per ). As described in , the use of identical configuration numbers between multiplexed (bundled) media descriptions is the default way of indicating compatible configurations in a bundle.

extends the SDP capability negotiation framework to allow endpoints to negotiate three additional SDP capabilities. In particular, this memo provides a mechanism to negotiate bandwidth ("b=" line), connection data ("c=" line), and session or media titles ("i=" line for each session or media). Name Notes Level Mux Category bcap Inherit the category SUM as applicable to b= attribute BINHERIT bcap-v0 Not Impacted BNORMAL ccap The connection address type MUST be identical across all the multiplexed "m=" lines BIDENTICAL ccap-v0 Not Impacted BNORMAL icap Not Impacted BNORMAL icap-v0 Not Impacted BNORMAL

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

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. Name Notes Level Mux Category fingerprint fingerprint value from the "m=" line defining the underlying transport is chosen BTRANSPORT

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. Name Notes Level Mux Category source-filter The attribute MUST be repeated across all "m=" lines multiplexed BIDENTICAL

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. removes this restriction by introducing a new SDP attribute. Name Notes Level Mux Category multicast-rtcp Multicast RTCP port MUST be identical across all the "m=" lines BIDENTICAL

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

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. Name Notes Level Mux Category setup The attribute MUST be identical across all "m=" lines BIDENTICAL connection Thee attribute MUST be identical across all "m=" lines BIDENTICAL

proposes a mechanism that allows the same SDP offer to carry multiple IP addresses of different address families (e.g., IPv4 and IPv6). The proposed attribute, the "altc" attribute, solves the backward-compatibility problem that plagued Alternative Network Address Types (ANAT) due to their syntax. Name Notes Level Mux Category altc The IP Address and port MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow MTRANSPORT

describes use cases, requirements, and protocol extensions for using the Session Description Protocol (SDP) offer/answer model for establishing audio and video media streams over circuit-switched bearers in the Public Switched Telephone Network (PSTN). Name Notes Level Mux Category cs-correlation:callerid Refer to notes below MTBD cs-correlation:uuie Refer to notes below M TBD cs-correlation:dtmf Refer to notes below MTBD cs-correlation:external Refer to notes below MTBD NOTE: defines SDP attributes for establishing audio and video media streams over circuit-switched bearers by defining a new nettype value "PSTN". However, section 7.2 of requires the "c=" line nettype value of 'IN'. If in future there exists a specification that defines procedures to multiplex media streams over nettype "PSTN", the multiplexing categories for attributes in this section MUST be revisited.

defines a new RTP Control Protocol (RTCP) Packet Type and an RTCP Extended Report (XR) Block Type to be used for achieving Inter-Destination Media Synchronization (IDMS). Name Notes Level Mux Category rtcp-idms Not Impacted MNORMAL

provides descriptions of Session Description Protocol (SDP) attributes used by the Open Mobile Alliance's Broadcast Service and Content Protection specification. Name Notes Level Mux Category bcastversion Not Impacted SNORMAL stkmstream Not Impacted BNORMAL SRTPAuthentication Needs further analysis MTBD SRTPROCTxRate Needs further analysis MTBD

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. Name Notes Level Mux Category ike-setup Attribute MUST be identical across all the "m=" lines BIDENTICAL psk-fingerprint Attribute MUST be identical across all the "m=" lines BIDENTICAL ike-esp Attribute MUST be identical across all the "m=" lines BIDENTICAL ike-esp-udpencap Attribute MUST be identical across all the "m=" lines BIDENTICAL NOTE: With the above SDP constraints, a session multiplexed with multiple "m=" lines will use only one IPSec association for all of the "m=" lines.

The Real Time Streaming Protocol, or RTSP, is an application-level protocol for control over the delivery of data with real-time properties. RTSP provides an extensible framework to enable controlled, on-demand delivery of real-time data, such as audio and video. Name Notes Level Mux Category etag RTSP is not supported for RTP Stream multiplexing BNOT RECOMMENDED range RTSP is not supported for RTP Stream multiplexing BNOT RECOMMENDED control RTSP is not supported for RTP Stream multiplexing BNOT RECOMMENDED mtag RTSP is not supported for RTP Stream multiplexing BNOT RECOMMENDED NOTE: defines SDP attributes that are applicable in the declarative usage of SDP alone. For purposes of this document, only the Offer/Answer usage of SDP is considered as mandated by .

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. provides information about these extensions and registers the RTSP and SDP extensions with IANA. Name Notes Level Mux Category X-predecbufsize Refer to notes below MNOT RECOMMENDED X-initpredecbufperiod Refer to notes below MNOT RECOMMENDED X-initpostdecbufperiod Refer to notes below MNOT RECOMMENDED X-decbyterateRefer to notes below MNOT RECOMMENDED 3gpp-videopostdecbufsize Refer to notes below MNOT RECOMMENDED framesizeRefer to notes below M NOT RECOMMENDED 3GPP-Integrity-Key Refer to notes below S NOT RECOMMENDED 3GPP-SDP-Auth Refer to notes below S NOT RECOMMENDED 3GPP-SRTP-Config Refer to notes below M NOT RECOMMENDED alt Refer to notes below MNOT RECOMMENDED alt-default-id Refer to notes below MNOT RECOMMENDED alt-group Refer to notes below M NOT RECOMMENDED 3GPP-Adaptation-Support Refer to notes below M NOT RECOMMENDED 3GPP-Asset-Information Refer to notes below B NOT RECOMMENDED mbms-mode Refer to notes below B NOT RECOMMENDED mbms-flowid Refer to notes below M NOT RECOMMENDED mbms-repair Refer to notes below B NOT RECOMMENDED 3GPP-QoE-Metrics Refer to notes below MNOT RECOMMENDED 3GPP-QoE-Metrics:Corruption duration Refer to notes below MNOT RECOMMENDED 3GPP-QoE-Metrics:Rebuffering duration Refer to notes below MNOT RECOMMENDED 3GPP-QoE-Metrics:Initial buffering duration Refer to notes below MNOT RECOMMENDED 3GPP-QoE-Metrics:Successive loss of RTP packets Refer to notes below MNOT RECOMMENDED 3GPP-QoE-Metrics:Frame rate deviation Refer to notes below MNOT RECOMMENDED 3GPP-QoE-Metrics:Jitter duration Refer to notes below MNOT RECOMMENDED 3GPP-QoE-Metrics:Content Switch Time Refer to notes below BNOT RECOMMENDED 3GPP-QoE-Metrics:Average Codec Bitrate Refer to notes below MNOT RECOMMENDED 3GPP-QoE-Metrics:Codec Information Refer to notes below MNOT RECOMMENDED 3GPP-QoE-Metrics:Buffer Status Refer to notes below MNOT RECOMMENDED NOTE: defines SDP attributes that are applicable in the declarative usage of SDP alone. For purposes of this document, only the Offer/Answer usage of SDP is considered as mandated by .

describes conventions for using the Session Description Protocol (SDP) described for controlling ATM Bearer Connections, and any associated ATM Adaptation Layer (AAL). Name Notes Level Mux Category aalType Refer to notes below B NOT RECOMMENDED eecid Refer to notes below B NOT RECOMMENDED capability Refer to notes below B NOT RECOMMENDED qosClass Refer to notes below B NOT RECOMMENDED bcob Refer to notes below B NOT RECOMMENDED stc Refer to notes below B NOT RECOMMENDED upcc Refer to notes below B NOT RECOMMENDED atmQOSparms Refer to notes below B NOT RECOMMENDED atmTrfcDesc Refer to notes below B NOT RECOMMENDED abrParms Refer to notes below B NOT RECOMMENDED abrSetup Refer to notes below B NOT RECOMMENDED bearerType Refer to notes below B NOT RECOMMENDED lij Refer to notes below B NOT RECOMMENDED anycast Refer to notes below B NOT RECOMMENDED cache Refer to notes below B NOT RECOMMENDED bearerSigIE Refer to notes below B NOT RECOMMENDED aalApp Refer to notes below B NOT RECOMMENDED cbrRate Refer to notes below B NOT RECOMMENDED sbc Refer to notes below B NOT RECOMMENDED clkrec Refer to notes below B NOT RECOMMENDED fec Refer to notes below B NOT RECOMMENDED prtfl Refer to notes below B NOT RECOMMENDED structure Refer to notes below B NOT RECOMMENDED cpsSDUsize Refer to notes below B NOT RECOMMENDED aal2CPS Refer to notes below B NOT RECOMMENDED aal2CPSSDUrate Refer to notes below B NOT RECOMMENDED aal2sscs3661unassured Refer to notes below B NOT RECOMMENDED aal2sscs3661assured Refer to notes below B NOT RECOMMENDED aal2sscs3662 Refer to notes below B NOT RECOMMENDED aal5sscop Refer to notes below B NOT RECOMMENDED atmmap Refer to notes below B NOT RECOMMENDED silenceSupp Refer to notes below B NOT RECOMMENDED ecan Refer to notes below B NOT RECOMMENDED gc Refer to notes below B NOT RECOMMENDED profileDesc Refer to notes below B NOT RECOMMENDED vsel Refer to notes below B NOT RECOMMENDED dsel Refer to notes below B NOT RECOMMENDED fsel Refer to notes below B NOT RECOMMENDED onewaySel Refer to notes below B NOT RECOMMENDED codecconfig Refer to notes below B NOT RECOMMENDED isup_usi Refer to notes below B NOT RECOMMENDED uiLayer1_Prot Refer to notes below B NOT RECOMMENDED chain Refer to notes below B NOT RECOMMENDED NOTE: RFC3108 describes conventions for using the Session Description Protocol (SDP) for characterizing ATM bearer connections using an AAL1, AAL2 or AAL5 adaptation layers. For AAL1, AAL2 and AAL5, bearer connections can be used to transport single media streams. In addition, for AAL1 and AAL2, multiple media streams MAY be multiplexed into a bearer connection. For all adaptation types (AAL1, AAL2 and AAL5), bearer connections MAY be bundled into a single media group. In all cases addressed by RFC3108, a real-time media stream (voice, video, voiceband data, pseudo-wire and others) or a multiplex of media streams is mapped directly into an ATM connection. RFC3108 does not address cases where ATM serves as a low-level transport pipe for IP packets which in turn MAY carry one or more real-time (e.g. VoIP) media sessions with a life-cycle different from that of the underlying ATM transport.

specifies IP multimedia subsystem: Media handling and interaction Name Notes Level Mux Category 3gpp_sync_info Usage defined for the IP Multimedia Subsystem MNORMAL 3gpp_MaxRecvSDUSize Usage defined for the IP Multimedia Subsystem MNORMAL

Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN); Name Notes Level Mux Category PSCid Not Impacted SNORMAL bc_service Not Impacted SNORMAL bc_program Not Impacted SNORMAL bc_service_package Not Impacted SNORMAL

specifies IP multimedia subsystem Custom Alerting tones Name Notes Level Mux Category g.3gpp.cat Usage defined for the IP Multimedia Subsystem MNORMAL

specifies IP multimedia subsystem Custom Ringing Signal Name Notes Level Mux Category g.3gpp.crs Usage defined for the IP Multimedia Subsystem MNORMAL

specifies IP multimedia call control protocol based on Session Initial protocol and Session Description Protocol. Name Notes Level Mux Category secondary-realm secondary-realm MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow M TRANSPORT visited-realm visited-realm MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow M TRANSPORT omr-m-cksum Not Impacted MNORMAL omr-s-cksum Not Impacted MNORMAL omr-m-att Not Impacted MNORMAL omr-s-att Not Impacted MNORMAL omr-m-bw Not Impacted MNORMAL omr-s-bw Not Impacted MNORMAL omr-codecs Not Impacted MNORMAL

defines procedures for real-time Group 3 facsimile communications over IP networks. Name Notes Level Mux Category T38FaxVersion Refer to notes below STBD T38MaxBitRate Refer to notes below STBD T38FaxFillBitRemoval Refer to notes below STBD T38FaxTranscodingMMR Refer to notes below STBD T38FaxTranscodingJBIG Refer to notes below STBD T38FaxRateManagement Refer to notes below STBD T38FaxMaxBuffer Refer to notes below STBD T38FaxMaxDatagram Refer to notes below STBD T38FaxUdpEC Refer to notes below STBD T38FaxMaxIFP Refer to notes below STBD T38FaxUdpECDepth Refer to notes below STBD T38FaxUdpFECMaxSpan Refer to notes below STBD T38ModemType Refer to notes below STBD T38VendorInfo Refer to notes below STBD NOTE: As per section 9.1 of , there exists no publicly available specification that defines procedures for multiplexing/demultiplexing fax protocols flows over a single 5-tuple. Once such a specification is available, the multiplexing category assignments for the attributes in this section MUST be revisited.

defines BICC IP bearer control protocol. Name Notes Level Mux Category ipbcp ipbcp version identifies type of IPBCP message used in BICC (ITU-T Q.1901) environment which are limited to single media payload. Pertinent ITU.T specifications needs to be referred while multiplexing SSPECIAL

ITU-T H.248.15 defines Gateway Control Protocol SDP H.248 package attribute Name Notes Level Mux Category h248item It is only applicable for signaling the inclusion of H.248 extension packages to a gateway via the local and remote descriptors. The attribute itself is unaffected by multiplexing, but the packaged referenced in a specific use of the attribute 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 BSPECIAL

the Message Session Relay Protocol, a protocol for transmitting a series of related instant messages in the context of a session. Message sessions are treated like any other media stream when set up via a rendezvous or session creation protocol such as the Session Initiation Protocol. Name Notes Level Mux Category accept-types Refer to notes below M TBD accept-wrapped-types Refer to notes below M TBD max-size Refer to notes below M TBD path Refer to notes below M TBD NOTE: As per section 9.1 of , there exists no publicly available specification that defines procedures for multiplexing/demultiplexing MRSP flows over a single 5-tuple. Once such a specification is available, the multiplexing categories assignments for the attributes in this section MUST be revisited.

This section specifies analysis for the attributes that are included for historic usage alone by the . Name Notes Level Mux Category rtpred1 Historic attributes MNOT RECOMMENDED rtpred2 Historic attributes MNOT RECOMMENDED

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

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

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. Name Notes Level Mux Category bwtype:TIAS The usage of TIAS is not clearly defined Offer/Answer usage. BSPECIAL maxprate The usage of TIAS and maxprate is not well defined under multiplexing BSPECIAL NOTE: The intention of TIAS is that the media level bit-rate is multiplied with the known per-packet overhead for the selected transport and the maxprate value to determine the worst case bit-rate from the transport to more accurately capture the required usage. Summing TIAS values independently across "m=" lines and multiplying the computed sum with maxprate and the per-packet overhead would inflate the value significantly. Instead performing multiplication and adding the individual values is a more appropriate usage.

This section analyzes rtcp-fb SDP attributes.

defines an extension to the Audio-visual Profile (AVP) that enables receivers to provide, statistically, more immediate feedback to the senders and thus allows for short-term adaptation and efficient feedback-based repair mechanisms to be implemented. Name Notes Level Mux Category ack rpsi The attribute value MUST be same for a given codec configuration MIDENTICAL-PER-PT ack app Feedback parameters MUST be handled in the app specific way when multiplexed MSPECIAL nack The attribute value MUST be same for a given codec configuration MIDENTICAL-PER-PT nack pli The attribute value MUST be same for a given codec configuration MIDENTICAL-PER-PT nack sli The attribute value MUST be same for a given codec configuration MIDENTICAL-PER-PT nack rpsi The attribute value MUST be same for a given codec configuration MIDENTICAL-PER-PT nack app Feedback parameters MUST be handled in the app specific way when multiplexed MSPECIAL trr-int The attribute value MUST be same for a given codec configuration MIDENTICAL-PER-PT

specifies how Explicit Congestion Notification (ECN) can be used with the Real-time Transport Protocol (RTP) running over UDP, using the RTP Control Protocol (RTCP) as a feedback mechanism. It defines a new RTCP Extended Report (XR) block for periodic ECN feedback, a new RTCP transport feedback message for timely reporting of congestion events, and a Session Traversal Utilities for NAT (STUN) extension used in the optional initialization method using Interactive Connectivity Establishment (ICE). Name Notes Level Mux Category ecn-capable-rtp ECN markup are enabled at the RTP session level M IDENTICAL nack ecn This attribute enables ECN at the RTP session level M IDENTICAL

In a large RTP session using the RTP Control Protocol (RTCP) feedback mechanism defined in , 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. 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. Name Notes Level Mux Category nack tllei The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT nack pslei The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT

specifies a few extensions to the messages defined in the Audio-Visual Profile with Feedback (AVPF). They are helpful primarily in conversational multimedia scenarios where centralized multipoint functionalities are in use. However, some are also usable in smaller multicast environments and point-to-point calls. Name Notes Level Mux Category ccm fir The attribute value MUST be same for a given codec configuration MIDENTICAL-PER-PT ccm tmmbr The attribute value MUST be same for a given codec configuration MIDENTICAL-PER-PT ccm tstr The attribute value MUST be same for a given codec configuration MIDENTICAL-PER-PT ccm vbcm The attribute value MUST be same for a given codec configuration MIDENTICAL-PER-PT

This section analyzes SDP "group" attribute semantics .

defines a framework to group "m" lines in the Session Description Protocol (SDP) for different purposes. Name Notes Level Mux Category group:LS Not Impacted S NORMAL group:FID Not Impacted S NORMAL

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). Name Notes Level Mux Category group:SRF Not Impacted S NORMAL

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. Name Notes Level Mux Category group:ANAT ANAT semantics is obseleted S NOT RECOMMENDED

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. Name Notes Level Mux Category group:FEC-FR Not Impacted S NORMAL

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. Name Notes Level Mux Category depend lay The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT depend mdc The attribute value MUST be same for a given codec configuration M IDENTICAL-PER-PT

defines the semantics for grouping redundant streams in the Session Description Protocol (SDP). The semantics defined in this document are to be used with the SDP Grouping Framework. Grouping semantics at the Synchronization Source (SSRC) level are also defined in this document for RTP streams using SSRC multiplexing. Name Notes Level Mux Category group:DUP Not Impacted S NORMAL

This section analyzes "ssrc-group" semantics.

This section analyzes QoS tokes specified with SDP.

defines procedures to negotiate QOS mechanisms using the Session Description Protocol (SDP) offer/answer model. Name Notes Level Mux Category rsvp rsvp attribute MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport flow BTRANSPORT nsis rsvp attribute MUST be the one that corresponds to the "m=" line chosen for setting up the underlying transport BTRANSPORT NOTE: A single DSCP code point per flow being multiplexed doesn't impact multiplexing since QOS mechanisms are signaled/scoped per flow. For scenarios that involve having different DSCP code points for packets being transmitted over the same 5-tuple, issues as discussed in need to be taken into consideration.

describes a payload format for generic Forward Error Correction (FEC) for media data encapsulated in RTP. It is based on the exclusive-or (parity) operation. The payload format allows end systems to apply protection using various protection lengths and levels, in addition to using various protection group sizes to adapt to different media and channel characteristics. It enables complete recovery of the protected packets or partial recovery of the critical parts of the payload depending on the packet loss situation. Name Notes Level Mux Category audio/ulpfec Not recommended for multiplexing due to reuse of SSRCs MNOT RECOMMENDED video/ulpfec Not recommended for multiplexing due to reuse of SSRCs MNOT RECOMMENDED text/ulpfec Not recommended for multiplexing due to reuse of SSRCs MNOT RECOMMENDED application/ulpfec Not recommended for multiplexing due to reuse of SSRCs MNOT RECOMMENDED

This sections deals with recommendations for defining the multiplexing characteristics of the SDP attributes that encapsulate other SDP attributes/parameters. Such attributes as of today, for example, are defined in , and as part of a generic framework for indicating and negotiating transport, media and media format related capabilities in the SDP. The behavior of such attributes under multiplexing is in turn defined by the multiplexing behavior of the attributes they encapsulate which are made known once the Offer/Answer negotiation process is completed.

capability parameter attribute (a=cpar) encapsulates b= (bandwidth) or an a= attribute. For bandwidth attribute encapsulation, the category SUM is inherited. For the case of a= attribute, the category corresponding to the SDP attribute being encapsulated is inherited.

In the above example,the category IDENTICAL is inherited for the cpar encapsulated rtcp-mux attribute.

defines a general SDP capability negotiation framework. It also specifies how to provide transport protocols and SDP attributes as capabilities and negotiate them using the framework. For this purpose, defines the following A set of capabilities for the session and its associated media stream components, supported by each side. The attribute ("a=acap") defines how to list an attribute name and its associated value (if any) as a capability. The attribute ("a=tcap") defines how to list transport protocols (e.g., "RTP/AVP") as capabilities. A set of potential configurations ("a=pcfg") provided by the offerer to indicate which combinations of those capabilities can be used for the session and its associated media stream components. Potential configurations are not ready for use until fully negotiated. They provide an alternative that MAY be used, subject to SDP capability negotiation procedures. In particular the answerer MAY choose one of the potential configurations for use as part of the current Offer/Answer exchange. An actual configuration ("a=acfg") for the session and its associated media stream components. The actual configuration identifies the potential configuration that was negotiated for use. Use of an actual configuration does not require any further negotiation. A negotiation process that takes the current actual and the set of potential configurations (combinations of capabilities) as input and provides the negotiated actual configurations as output. In the negotiation process is done independently for each media description.

This section provides recommendations for entities generating and processing SDP under the generic capability negotiation framework as defined in under the context of media stream multiplexing. These recommendations are provided for the purposes of enabling the Offerer to make sure that the generated potential configurations between the multiplexed streams can (easily) be negotiated to be consistent between those streams. In particular, the procedures aim to simplify Answerer's procedure to choose potential configurations that are consistent across all the multiplexed media descriptions. A potential configuration selects a set of attributes and parameters that become part of the media description when negotiated. When multiplexing media descriptions with potential configurations specified, there MAY be a need for coordinating this selection between multiplexed media descriptions to ensure the right multiplexing behavior. Although it is possible to analyze the various potential configurations in multiplexed media descriptions to find combinations that satisfy such constraints, it can quickly become complicated to do so. The procedures defined in state that each potential configuration in the SDP has a unique configuration number, however the scope of uniqueness is limited to each media description. To make it simple for the answerer to chose valid combinations of potential configurations across media descriptions in a given bundle group, we provide a simple rule for constructing potential configurations Let m-bundle be the set of media descriptions that form a given bundle . Let m-bundle-pcfg be the set of media descriptions in m-bundle that include one or more potential configurations. Each media description in m-bundle-pcfg MUST have at least one potential configuration with the same configuration number (e.g. "1"). For each potential configuration with configuration number x in m-bundle-pcfg, the offerer MUST ensure that if the answerer chooses configuration number x in each of the media descriptions in m-bundle-pcfg, then the resulting SDP will have all multiplexing constraints satisfied for those media descriptions. Since it is nearly impossible to define a generic mechanism for various capability extensions, this document does't provide procedures for dealing with the capability extension attributes. However, provide analysis of media capability extension attributes as defined in . The above allows the answerer to easily find multiplexing compatible combinations of potential configurations: The answerer simply choses a potential configuration (number) that is present in all of the media descriptions with potential configurations in the bundle. Note that it is still possible for the offerer to provide additional potential configurations with independent configuration numbers. The answerer will have to perform more complicated analysis to determine valid multiplexed combinations of those.

In the example above, the potential configurations that offer transport protocol capability of RTP/SAVPF has the same configuration number "1" in both the audio and video media descriptions.

In the example above, the potential configuration number "1" is repeated while referring to attribute capability a=rtcp-mux, since the behavior is IDENTICAL for the attribute a=rtcp-mux under multiplexing.

extends capability negotiation framework described in by defining media capabilities that can be used to indicate and negotiate media types and their associated format parameters. It also allows indication of latent configurations and session capabilities.

defines a new payload type ("pt") parameter to be used with the potential, actual and latent configuration parameters. The parameter associates RTP payload type numbers with the referenced RTP-based media format capabilities ("a=rmcap") defined in and is appropriate only when the transport protocol uses RTP. This means that the same payload type number can be assigned as part of potential or actual configurations in different media descriptions in a bundle. There are rules for the usage of identical Payload Type values across multiplexed "m=" lines as described in , which MUST be followed here as well. As described in , the use of identical configuration numbers for compatible configurations in different media descriptions that are part of the bundle provides a way to ensure that the answerer can easily pick compatible configurations here as well.

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

In the example above, the potential configuration number "1" is repeated when referring to media and media format capability used for the Payload Type 96. This implies that both the media capability 2 and 4 along with their media format capabilities MUST refer to the same codec configuration, as per the definition of IDENTICAL-PER-PT.

adds the notion of a latent configurations, which provides configuration information that may be used to guide a subsequent offer/exchange, e.g. by adding another media stream or use alternative codec combinations not currently offered. Latent configurations have configuration numbers which cannot overlap with the potential configuration numbers . Supported combinations of potential and latent configurations are indicated by use of the "a=sescap" attribute, however use of this attribute is NOT RECOMMENDED with multiplexed media, since it requires the use of unique configuration numbers across the SDP. Taken together, this means there is no well-defined way to indicate supported combinations of latent configurations, or combinations of latent and potential configurations with multiplexed media. It is still allowed to use the latent configuration attribute, however the limitations above will apply. To determine valid combinations, actual negotiation will have to be attempted subsequently instead.

[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this document.] The IANA is requested to add a new column named "Mux Category" to several of the subregistries in the "Session Description Protocol (SDP) Parameters" registry. defines a new subregistry for identifying the initial registrations for various multiplexing categories applicable, as proposed in this document. The tables in identify name of an entry in the existing subregistry and specify the value to put in the new "Mux Category" column of the associated IANA registry. Any entries in the existing tables that do not have a value for the "Mux Category" specified in this RFC will get a value of "TBD". Future specifications can change the "TBD" entries to the correct value.

A new sub-registry needs to be defined called the "Multiplexing Categories", with the following registrations created initially: "NORMAL", "NOT RECOMMENDED", "IDENTICAL", "TRANSPORT", "SUM", "INHERIT", "IDENTICAL-PER-PT", "SPECIAL" and "TBD" as defined in this document. Initial value registration for "Multiplexing Categories". Multiplexing Categories Reference NORMAL RFCXXXX NOT RECOMMENDED RFCXXXX IDENTICAL RFCXXXX TRANSPORT RFCXXXX SUM RFCXXXX INHERIT RFCXXXX IDENTICAL-PER-PT RFCXXXX SPECIAL RFCXXXX TBD RFCXXXX Further entries may be registered on a first-come first-serve basis. Each registration needs to indicate the multiplexing category value to be added to the "Multiplexing Categories" subregistry as defined in this section. Such a registration MUST also indicate the applicability of the newly defined multiplexing category value to various subregistries defined at "Session Description Protocol (SDP) Parameters". The general registration procedures of apply.

Each sub-section identifies a subregistry in the "Session Description Protocol (SDP) Parameters" registry. The tables list the column that identifies the SDP attribute name/Token/Value from the corresponding subregistries and the values to be used for the new "Mux Category" column to be added.

The following values are to be added to the 'SDP bwtype' subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. SDP Name Mux Category CT NORMAL AS SUM RS SUM RR SUM TIAS SPECIAL

The following values are to be added to the "att-field (session level)" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. SDP Name Mux Category cat NORMAL keywds NORMAL type NORMAL type:broadcast NORMAL type:H332 NORMAL type:meeting NORMAL type:moderated NORMAL type:test NORMAL charset NORMAL charset:iso8895-1 NORMAL tool NORMAL ipbcp SPECIAL group NORMAL ice-lite NORMAL ice-options NORMAL bcastversion NORMAL 3GPP-Integrity-Key NOT RECOMMENDED 3GPP-SDP-Auth NOT RECOMMENDED alt-group NOT RECOMMENDED PSCid NORMAL bc_service NORMAL bc_program NORMAL bc_service_package NORMAL sescap NOT RECOMMENDED rtsp-ice-d-m NOT RECOMMENDED

The following values are to be added to the "att-field (both session and media level)" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. NOTE: The attributes from draft-ietf-rmt-flute-sdp ('flute-tsi', 'flute-ch', 'FEC-declaration', 'FEC-OTI-extension', 'content-desc') were not analyzed for their multiplexing behavior due to the expired status of the draft. For purposes of this specification, the multiplexing category of 'TBD' is assigned. SDP Name Mux Category recvonly NORMAL sendrecv NORMAL sendonly NORMAL sdplang NORMAL lang NORMAL h248item SPECIAL sqn NORMAL cdsc NORMAL cpar INHERIT cparmin SPECIAL cparmax SPECIAL rtcp-xr NORMAL maxprate SPECIAL setup IDENTICAL connection IDENTICAL key-mgmt IDENTICAL source-filter IDENTICAL inactive NORMAL fingerprint TRANSPORT flute-tsi TBD flute-ch TBD FEC-declaration TBD FEC-OTI-extension TBD content-desc TBD ice-pwd TRANSPORT ice-ufrag TRANSPORT stkmstream NORMAL extmap SPECIAL qos-mech-send NORMAL qos-mech-recv NORMAL csup NORMAL creq NORMAL acap INHERIT tcap INHERIT 3GPP-QoE-Metrics NOT RECOMMENDED 3GPP-Asset-Information NOT RECOMMENDED mbms-mode NOT RECOMMENDED mbms-repair NOT RECOMMENDED ike-setup IDENTICAL psk-fingerprint IDENTICAL multicast-rtcp IDENTICAL rmcap IDENTICAL-PER-PT omcap NORMAL mfcap IDENTICAL-PER-PT mscap INHERIT 3gpp.iut.replication TBD bcap INHERIT ccap IDENTICAL icap NORMAL 3gpp_sync_info NORMAL 3gpp_MaxRecvSDUSize NORMAL etag NOT RECOMMENDED duplication-delay NORMAL range NOT RECOMMENDED control NOT RECOMMENDED mtag NOT RECOMMENDED ts-refclk NORMAL mediaclk NORMAL calgextmap NORMAL

The following values are to be added to the "att-field (media level only)" registry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. SDP Name Mux Category ptime IDENTICAL-PER-PT orient NORMAL orient:portrait NORMAL orient:landscape NORMAL orient:seascape NORMAL framerate IDENTICAL-PER-PT quality NORMAL rtpmap IDENTICAL-PER-PT fmtp IDENTICAL-PER-PT rtpred1 NOT RECOMMENDED rtpred2 NOT RECOMMENDED T38FaxVersion TBD T38MaxBitRate TBD T38FaxFillBitRemoval TBD T38FaxTranscodingMMR TBD T38FaxTranscodingJBIG TBD T38FaxRateManagement TBD T38FaxMaxBuffer TBD T38FaxMaxDatagram TBD T38FaxUdpEC TBD maxptime IDENTICAL-PER-PT des NOT RECOMMENDED curr NOT RECOMMENDED conf NOT RECOMMENDED mid NORMAL rtcp TRANSPORT rtcp-fb IDENTICAL-PER-PT label NORMAL T38VendorInfo TBD crypto TRANSPORT eecid NOT RECOMMENDED aalType NOT RECOMMENDED capability NOT RECOMMENDED qosClass NOT RECOMMENDED bcob NOT RECOMMENDED stc NOT RECOMMENDED upcc NOT RECOMMENDED atmQOSparms NOT RECOMMENDED atmTrfcDesc NOT RECOMMENDED abrParms NOT RECOMMENDED abrSetup NOT RECOMMENDED bearerType NOT RECOMMENDED lij NOT RECOMMENDED anycast NOT RECOMMENDED cache NOT RECOMMENDED bearerSigIE NOT RECOMMENDED aalApp NOT RECOMMENDED cbrRate NOT RECOMMENDED sbc NOT RECOMMENDED clkrec NOT RECOMMENDED fec NOT RECOMMENDED prtfl NOT RECOMMENDED structure NOT RECOMMENDED cpsSDUsize NOT RECOMMENDED all2CPS NOT RECOMMENDED all2CPSSDUrate NOT RECOMMENDED aal2sscs3661unassured NOT RECOMMENDED aal2sscs3661assured NOT RECOMMENDED aal2sscs3662 NOT RECOMMENDED aal5sscop NOT RECOMMENDED atmmap NOT RECOMMENDED silenceSupp NOT RECOMMENDED ecan NOT RECOMMENDED gc NOT RECOMMENDED profileDesc NOT RECOMMENDED vsel NOT RECOMMENDED dsel NOT RECOMMENDED fsel NOT RECOMMENDED onewaySel NOT RECOMMENDED codecConfig NOT RECOMMENDED isup_usi NOT RECOMMENDED uiLayer1_Prot NOT RECOMMENDED chain NOT RECOMMENDED floorctrl IDENTICAL confid NORMAL userid NORMAL floorid NORMAL FEC NORMAL accept-types TBD accept-wrapped-types TBD max-size TBD path TBD dccp-service-code NOT RECOMMENDED rtcp-mux IDENTICAL candidate TRANSPORT ice-mismatch NORMAL remote-candidates TRANSPORT SRTPAuthentication TBD SRTPROCTxRate TBD rtcp-rsize IDENTICAL file-selector TBD file-transfer-id TBD file-disposition TBD file-date TBD file-icon TBD file-range NORMAL depend TBD-PER-PT ssrc NORMAL ssrc-group NORMAL rtcp-unicast IDENTICAL pcfg SPECIAL acfg SPECIAL zrtp-hash TRANSPORT X-predecbufsize NOT RECOMMENDED X-initpredecbufperiod NOT RECOMMENDED X-initpostdecbufperiod NOT RECOMMENDED X-decbyterate NOT RECOMMENDED 3gpp-videopostdecbufsize NOT RECOMMENDED framesize NOT RECOMMENDED 3GPP-SRTP-Config NOT RECOMMENDED alt NOT RECOMMENDED alt-default-id NOT RECOMMENDED 3GPP-Adaption-Support NOT RECOMMENDED mbms-flowid NOT RECOMMENDED fec-source-flow SPECIAL fec-repair-flow SPECIAL repair-window SPECIAL rams-updates NOT RECOMMENDED imageattr IDENTICAL-PER-PT cfw-id NORMAL portmapping-req NOT RECOMMENDED g.3gpp.cat NORMAL g.3gpp.crs NORMAL ecn-capable-rtp IDENTICAL visited-realm TRANSPORT secondary-realm TRANSPORT omr-s-cksum NORMAL omr-m-cksum NORMAL omr-codecs NORMAL omr-m-att NORMAL omr-s-att NORMAL omr-m-bw NORMAL omr-s-bw NORMAL msrp-cema TBD dccp-port NOT RECOMMENDED resource NORMAL channel NORMAL cmid NORMAL content NORMAL lcfg SPECIAL loopback NORMAL loopback-source NORMAL loopback-mirror NORMAL chatroom TBD altc TRANSPORT T38FaxMaxIFP TBD T38FaxUdpECDepth TBD T38FaxUdpFECMaxSpan TBD T38ModemType TBD cs-correlation TBD rtcp-idms NORMAL

The following values are to be added to the "att-field (source level)" registry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. SDP Name Mux Category cname NORMAL previous-ssrc NORMAL fmtp IDENTICAL-PER-PT ts-refclk NORMAL mediaclk NORMAL

The following values are to be added to the "content SDP Parameters" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. SDP Name Mux Category slides NORMAL speaker NORMAL sl NORMAL main NORMAL alt NORMAL

The following values are to be added to the "Semantics for the "group" SDP Attribute" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. Token Mux Category LS NORMAL FID NORMAL SRF NORMAL ANAT NOT RECOMMENDED FEC NORMAL FEC-FR NORMAL CS NORMAL DDP NORMAL DUP NORMAL

The following values are to be added to the " 'rtcp-fb' Attribute Values" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. Value Name Mux Category ack IDENTICAL-PER-PT app SPECIAL ccm IDENTICAL-PER-PT nack IDENTICAL-PER-PT trr-int IDENTICAL-PER-PT

The following values are to be added to the " 'ack' and 'nack' Attribute Values" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. Value Name Mux Category sli IDENTICAL-PER-PT pli IDENTICAL-PER-PT rpsi IDENTICAL-PER-PT app SPECIAL rai IDENTICAL-PER-PT tllei IDENTICAL-PER-PT pslei IDENTICAL-PER-PT ecn IDENTICAL

The following values are to be added to the " 'depend' SDP Attribute Values" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. Token Mux Category lay IDENTICAL-PER-PT mdc IDENTICAL-PER-PT

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

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

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

The following values are to be added to the "Codec Control Messages" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. Value Name Mux Category fir IDENTICAL-PER-PT tmmbr IDENTICAL-PER-PT tstr IDENTICAL-PER-PT vbcm IDENTICAL-PER-PT

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

The following values are to be added to the "SDP Capability Negotiation Option Tags" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. QoS Mechanism Mux Category cap-v0 NORMAL med-v0 NORMAL bcap-v0 NORMAL ccap-v0 NORMAL icap-v0 NORMAL

The following values are to be added to the "Timestamp Reference Clock Source Parameters" subregistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. Name Mux Category ntp NORMAL ptp NORMAL gps NORMAL gal NORMAL glonass NORMAL local NORMAL private NORMAL

The following values are to be added to the "Media Clock Source Parameters" subegistry in the "Session Description Protocol (SDP) Parameters" registry. The references should be updated to point at this RFC as well as the previous references. Name Mux Category sender NORMAL direct NORMAL IEEE1722 NORMAL

This document does not add any new security considerations beyond the existing considerations in the RFCs for protocols that are being multiplexed together. The ways that SRTP streams are keyed is not believed to create any two-time pad vulnerability for the currently defined SRTP keying mechanism.

I would like to thank Cullen Jennings, Flemming Andreasen for suggesting the categories, contributing text and reviewing the draft. I would also link to thank Magnus Westerlund, Christer Holmberg, Jonathan Lennox, Bo Burman, Ari Keranen, and Dan Wing on suggesting structural changes helping improve the document readability. I would like also to thank following experts on their inputs and reviews as listed - Flemming Andreasen(5.24,5.32,5.33,14), Rohan Mahy(5.57), Eric Burger(5.26),Christian Huitema(5.14), Christer Holmberg(5.21,5.26,5.51,5.52), Richard Ejzak (5.44,5.53,5.54), Colin Perkins(5.7,5.8,5.9,5.58), Magnus Westerlund(5.2,5.3,5.9,5.27,5.47,6.1,6.2,6.3,8.3,7), Roni Evens(5.12,5.27,8.4), Subha Dhesikan(5.6,10), Dan Wing(5.7,5.12,5.35,5.39,5.45), Cullen Jennings (5.40), Ali C Begen(5.1,5.20,5.22,5.25,5.38,7.3,8.2,8.4,8.6,9.2,13.1), Bo Burman (7.2,7.6), Charles Eckel(5.15,5.27,5.28,9.1,8.5), Paul Kyzivat(5.24), Ian Johansson(5.15), Saravanan Shanmugham(5.11), Paul E Jones(5.30), Rajesh Kumar(5.48), Jonathan Lennox(5.36,5,15,9.1,11.1), Mo Zanaty(5.4,5.5,5.23,8.1,8.3,8.5,12.1), Christian Huitema (5.14), Qin Wu (5.47 PM-Dir review), Hans Stokking(5.43,5.16), Christian Groves (5.48,5.55), Thomas Stach.

[RFC EDITOR NOTE: Please remove this section when publishing] Changes from draft-ietf-mmusic-sdp-mux-attributes-06 - 08 Assigned TBD category to all the attributes for whom there exists no specification on multiplexing behavior over the underlying transport protocol today. Incorporated comments from Flemming and Ari (post last call) Changes from draft-ietf-mmusic-sdp-mux-attributes-06 Incorporated last call review comments from Thomas Stach and Ari Keranen. Fixed more nits to prep for the LastCall. Changes from draft-ietf-mmusic-sdp-mux-attributes-05 Incorporated review comments from Christian Grooves and Ari Keranen. Fixed more nits to prep for the LastCall. Changes from draft-ietf-mmusic-sdp-mux-attributes-04 Fixed minor nits overall. Updated Acknowledgement Sections Last Call Version. Changes from draft-ietf-mmusic-sdp-mux-attributes-03 More re-work on the IANA section. Clean ups preparing for the last call. Changes from draft-ietf-mmusic-sdp-mux-attributes-02 Incorporated suggestions from Flemming on Capability Negotiation. Closed open issues from IETF90 Added IANA section to list the categories for all the SDP attributes anlayzed Lots of cleanup Reformatted Refernces section to use short-form notation Changes from draft-ietf-mmusic-sdp-mux-attributes-01 Updated section 15 to provide detailed recommendation on dealing with encapsulating attributes. Also updated sections 5.20, 5.28, 5.29 to refer to Section 15. Added new categories IDENTICAL-PER-PT and INHERIT Updated Sections 16 to add the new categories. Updated Sections 5.1, 5.14, 5.15, 5.38, 8.5 to reflect the category IDENTICAL-PER-PT. Reformatted section 4 to add individual categories to their own sections. Changes from draft-ietf-mmusic-sdp-mux-attributes-00 Added Section 15 to provide recommendations on multiplexing SDP encapsulating attributes. Also updated sections 5.20, 5.28, 5.29 to refer to Section 15. Updated Section 5.38 to incorporate PM-dir review inputs from Qin Wu Updated Sections 5.2,5.14,8.5 to refer to BUNDLE draft for more clarity. Fixed few nits regarding sentence clarity and fill-in the NOTES section where information was lacking. Changes from draft-nandakumar-mmusic-mux-attributes-05 Renamed the document to be a WG document. Added Section 14. Updated Open Issues based on IETF88 discussions. Changes from draft-nandakumar-mmusic-mux-attributes-04 Added few OPEN ISSUES that needs to be discussed. Updated sections 5.10,5.23,5,24,5,25,7.2,9.1,5.12,5.27,8.4, 5.44,5.11,5.4,5.19,10.1,10.5,5.21,10.4,15.1 Updated Table Column name Current to Level and improved TRANSPORT category explanation on suggestions form Dan Wing. Grouped all the rtcp-fb attribute analysis under a single section as suggested by Magnus/ Changes from draft-nandakumar-mmusic-mux-attributes-03 Maintenance change to clean up grammatical nits and wordings. Changes from draft-nandakumar-mmusic-mux-attributes-02 Updated Sections 5.3,5.5,5.6,5.7,5.9,5.8,5.11,5.13,5.22,5.34, 5.37,5.40,5.41,5.42,5.43,5.44,5.45,6.1,6.2,6.3,8,3,12.1 based on the inputs from the respective RFC Authors. Changes from draft-nandakumar-mmusic-mux-attributes-01 Replaced Category BAD with NOT RECOMMENDED. Added Category TBD. Updated IANA Consideration Section. Changes from draft-nandakumar-mmusic-mux-attributes-00 Added new section for dealing with FEC payload types.