WG Review: Media Server Control (mediactrl)

[IESG Secretary <[e-mail]>]

A new IETF working group has been proposed in the RAI Area.  The IESG
has not made any determination as yet. The following draft charter was 
submitted, and is provided for informational purposes only. Please send 
your comments to the IESG mailing list ([e-mail]) by February 19.

+++

Media Server Control (mediactrl)
=================================

Current Status: Proposed Working Group

Chairs: 
TBD

RAI Area Director(s): 
Cullen Jennings <[e-mail]>
Jon Peterson <[e-mail]>

RAI Area Advisor: 
TBD

Mailing Lists: 
General Discussion: [e-mail]
Subscribe at: https://www1.ietf.org/mailman/listinfo/mediactrl
Archive at: http://www1.ietf.org/mail-archive/web/mediactrl


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, 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.

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 liaise with, and 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 liaise with,
and gather requirements from, ATIS and ETSI TISPAN.

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.

MILESTONES

APR 2007 Requirements Document
JUN 2007 Framework Document
NOV 2007 Conference Control Protocol
MAR 2008 IVR Control Protocol
JUN 2008 Broker Protocol or BCP

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