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Media Server Control

IETF Opens New Media Server Control Working Group

IESG Secretary. 2007-03-20.

A new IETF working group has been formed in the Real-time Applications and Infrastructure Area. For additional information, please contact the Area Directors or the WG Chairs.

Media Server Control (mediactrl)

Current Status: Active Working Group


Eric Burger

RAI Area Director(s)

Cullen Jennings
Jon Peterson

RAI Area Advisor

Jon Peterson

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Associated RFCs (Requests for Comments)

Basic Network Media Services with the Session Initiation Protocol (SIP)
(RFC 4240)

Media Server Control Markup Language (MSCML) and Protocol
(RFC 4722)

Description of the Working Group

Real-time multi-media applications often need the services of media processing elements. It is true that modern endpoints are capable of media processing. However, the physics of some media processing applications dictate that it is much more efficient for the media processing to occur at a centralized location. By media processing, we mean media mixing, recording and playing media, and interacting with a user in the audio or video domains. The commercial market calls these media processing network elements "media servers."

Some services achieve significant efficiencies when a central node performs media processing. Because of these efficiencies, media servers are widely used for conference mixing, multimedia messaging, content rendering, and speech, voice, key press, and other audio and video input and output user interface modalities. Given the wide acceptance of the media server, we need a standard way to control them.

Since the media server is a centralized component, the work group will not investigate distributed media processing algorithms or control protocols.

A media server contains media processing components that are able to manipulate RTP streams. Typical processing includes mixing multiple streams, transcoding a stream (e.g., from G.711 to MS-GSM), storing or retrieving a stream (e.g., from RTP to HTTP), detecting tones (e.g., DTMF), converting text to speech, and performing speech recognition.

Note that an MRCPv2 server may offer the low-level processing for the last two services, where the media server is a client to the MRCPv2 server. Also note it is common to call the package of detecting user input, recording media, and playing media "Interactive Voice Response," or IVR. Media services offered by the media server are addressed using SIP mechanisms, such as described in RFC 4240. Media servers commonly have a built-in VoiceXML interpreter. VoiceXML describes the elements of the user interaction, and is a proven model for separating application logic (which run on the clients of the media server) from the user interface (which the media server renders). Note this is a fundamentally different interaction model from MRCPv2, where media processing engines offer raw, low-level speech services.

The work group will examine protocol extensions between media servers and their clients. However, modifying existing standard protocols, such as VoiceXML or SIP towards clients or MRCPv2 towards servers, is not in the work group's charter. The model of interest to this group is where the endpoint solely plays audio or video, transmits audio or video towards the server, and possibly transmits key press information towards the server. Alternate architectures, where the endpoint executes user interface commands, is outside the scope of the work group. For example, WIDEX/BEEP, with its distributed user interface description, is not in scope.

The only model of user interface processing the work group will consider is where the media server performs all of the media processing. A caveat here is the media server, in interpreting a VoiceXML page, may make requests to a server for speech services. However, to the media server client and the media end point, the single point of signaling and media interaction is the media server.

Any protocol developed by this group will meet the requirements for Internet deployment. This includes addressing Internet security, privacy, congestion control (or at least congestion safe), operational and manageability considerations, and scale. The protocol will not assume a private administrative domain. There is broad market acceptance of the stimulus/markup application design model for the application server - media server protocol interface. Thus this work group will focus on the use of SIP and XML for the protocol suite.

The work product of this group includes the following:

  1. A requirements document. This document will identify and enumerate requirements for a suite of media server control protocols. Given that one of the common media server clients is a conference application server, we will consider the application server - media server requirements developed by the XCON work group. Likewise, we will consider media server control requirements from other standards groups, such as 3GPP SA2 and CT1.

  2. A framework document. This document will describe the different network elements, their interrelationship, and the broad set of message flows between them.

  3. A protocol suite describing the embodiment of the framework document. There may be separate protocol PDU's for audio conference control, video conference control, interactive audio (voice) response, and interactive video (multimedia) response. The separation and negotiation of different PDU's is a working group topic. However, there will be one and only one (class) of PDU's defined by the work group.

  4. Means for locating, and possibly establishing sessions to, media servers with appropriate resources at the request of clients. By appropriate, we mean the characteristics of a given media server required or desired for handling a given request. The expectation is such a means would build upon existing SIP, SNMP, and other protocol facilities. Such a means may or may not be an integral part of the item 3 deliverables above. This deliverable is an operational protocol that may rely on management protocols such as SNMP. We are neither creating a new management protocol nor a new provisioning protocol.

Given the above-mentioned conferencing example, the work of this group is of interest to the XCON work group, as this protocol will describe the "Protocol used between the conference controller and the mixer(s)." Thus we expect to work closely with XCON. The protocol suite also is a possible embodiment of the ISC/Mr interface from the 3GPP IMS architecture. Thus we expect to gather requirements from, 3GPP, notably SA2, CT1, and CT4. ATIS and ETSI TISPAN have considered a functional element known as a media resource broker. The media resource broker provides the functionality described by deliverable #4, above. Thus we expect to gather requirements from ATIS and ETSI TISPAN. The Java Community Process has chartered work on a Java Media Server Control (JMSC) API, known as JSR 309. We expect to gather requirements from JCP, as well.

Because of the vast experience with conferencing protocols and payloads, we expect considerable interaction with AVT and MMUSIC. If the work group requires extensions to SIP, the work group will forward those extensions to the SIP work group for consideration and refinement.


MAY 2007 Requirements Document WGLC
JUN 2007 Requirements Document to IESG (Informational)
JUN 2007 Framework Document WGLC
JUL 2007 Framework Document to IESG (Informational)
NOV 2007 Mixer Control Protocol WGLC
DEC 2007 Mixer Control Protocol to IESG (Standards Track)
MAR 2008 IVR Control Protocol WGLC
APR 2008 IVR Control Protocol to IESG (Standards Track)
JUN 2008 Broker Protocol WGLC
JUL 2008 Broker Protocol (Standards Track or BCP, TBD)

Prepared by Robin Cover for The XML Cover Pages archive.

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