Media Server Control

Document Charter Media Server Control WG (mediactrl)
Title Media Server Control
Last updated 2007-02-22
State Approved
WG State Concluded
IESG Responsible AD Richard Barnes
Charter Edit AD (None)
Send notices to (None)


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 
  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 
  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 
  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