Network Working Group M. Dolly
Request for Comments: 5167 AT&T Labs
Category: Informational R. Even
Polycom
March 2008
Media Server Control Protocol Requirements
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Abstract
This document addresses the communication between an application
server and media server. The current work in IETF working groups
shows these logical entities, but it does not address the physical
decomposition and the protocol between the entities.
This document presents the requirements for a Media Server Control
Protocol (MCP) that enables an application server to use a media
server. It will address the aspects of announcements, Interactive
Voice Response, and conferencing media services.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Media Control Requirements . . . . . . . . . . . . . . . . 3
3.2. Media mixing Requirements . . . . . . . . . . . . . . . . . 5
3.3. IVR Requirements . . . . . . . . . . . . . . . . . . . . . 6
3.4. Operational Requirements . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Informative References . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
The IETF conferencing framework in RFC 4353 [CARCH] presents an
architecture that is built of several functional entities. RFC 4353
[CARCH] does not specify the protocols between the functional
entities since it is considered out of scope.
Based on RFC 4353 [CARCH], this document defines the requirements for
a protocol that will enable one functional entity, known as an
Application Server (AS), that includes the conference/media policy
server, the notification server, and the focus, all defined in RFC
4353 [CARCH], to interact with one or more functional entities,
called Media Server (MS), that serves as mixer or media server.
The media server can also be used for announcements and Interactive
Voice Response (IVR) functions.
Application servers host one or more instances of a communication
application. Media servers provide real time media processing
functions. An example of the decomposition of a media server and an
application server is described in the media control framework
document [MEDIACTRL-FW].
This document presents the requirements for a Media Server Control
Protocol (MCP) that enables an application server to control a media
server. It will address the aspects of announcements, IVR, and
conferencing media services.
The requirements are for the protocol and do not address the AS or MS
functionality discussed in the media control framework.
Since the media server is a centralized component, the charter of the
working group states that this work will not investigate distributed
media processing algorithms or control protocols.
2. Terminology
The media server work uses, when appropriate, and expands on the
terminology introduced in the conferencing framework [CARCH] and
Centralized Conferencing (XCON) framework [XCON-FRMWRK]. The
following additional terms are defined:
Application Server (AS) - A functional entity that hosts one or more
instances of a communication application. The application server may
include the conference policy server, the focus, and the conference
notification server, as defined in [CARCH]. Also, it may include
communication applications that use IVR or announcement services.
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Media Server (MS) - The media server includes the mixer as defined in
[CARCH]. The media server plays announcements, it processes media
streams for functions like Dual Tone Multi-Frequency (DTMF) detection
and transcoding. The media server may also record media streams for
supporting IVR functions like announcing participants
Media Resource Broker (MRB) - A logical entity that is responsible
for both the collection of appropriate published Media Server (MS)
information and supplying of appropriate MS information to consuming
entities. The MRB is an optional entity and will be discussed in a
separate document.
Notification - A notification is used when there is a need to report
event-related information from the MS to the AS.
Request - A request is sent from the controlling entity, such as an
application server, to another resource, such as a media server,
asking that a particular type of operation be executed.
Response - A response is used to signal information, such as an
acknowledgement or error code in reply to a previously issued
request.
3. Requirements
3.1. Media Control Requirements
The following are the media control requirements:
REQ-MCP-01 - The MS Control Protocol shall enable one or more
application servers to request media services from one or more
media servers.
REQ-MCP-02 - The MS Control Protocol shall use a reliable transport
protocol.
REQ-MCP-03 - The applications supported by the protocol shall
include conferencing and Interactive Voice Response media
services.
Note: Though the protocol enables these services, the functionality
is invoked through other mechanisms.
REQ-MCP-04 - Media types supported in the context of the
applications shall include audio, tones, text, and video. Tones
media include in-band audio or RFC 4733 payload.
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REQ-MCP-05 - The MS control protocol should allow, but must not
require, a media resource broker (MRB) or intermediate proxy to
exist with the application server and media server.
REQ-MCP-06 - On the MS control channel, there shall be requests to
the MS, responses from the MS, and notifications to the AS.
REQ-MCP-07 - SIP/SDP (Session Initiation Protocol / Session
Description Protocol) shall be used to establish and modify media
connections to a media server.
REQ-MCP-08 - It should be possible to support a single conference
spanning multiple media servers.
Note: It is probable that spanning multiple MSs can be
accomplished by the AS and does not require anything in the
protocol for the scenarios we have in mind. However, the concern
is that if this requirement is treated too lightly, one may end up
with a protocol that precludes its support.
REQ-MCP-09 - It must be possible to split call legs individually, or
in groups, away from a main conference on a given media server,
without performing re-establishment of the call legs to the MS
(e.g., for purposes such as performing IVR with a single call leg
or creating sub-conferences, not for creating entirely new
conferences).
REQ-MCP-10 - The MS control protocol should be extendable,
facilitating forward and backward compatibility.
REQ-MCP-11 - The MS control protocol shall include an authentication
component to ensure that only an authorized AS can communicate
with the MS, and vice versa.
REQ-MCP-12 - The MS control protocol shall use some form of
transport protection to ensure the confidentiality and integrity
of the data between the AS and MS.
REQ-MCP-13 - Different application servers may have different
privileges for using an MS. The protocol should prevent the AS
from doing unauthorized operations on a MS.
REQ-MCP-14 - The MS control protocol requires mechanisms to protect
the MS resources used by one AS from another AS since the solution
needs to support multiple ASs controlling one MS.
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REQ-MCP-15 - During session establishment, there shall be a
capability to negotiate parameters that are associated with media
streams. This requirement should also enable an AS managing
conference to specify the media streams allowed in the conference.
REQ-MCP-16 - The AS shall be able to instruct the MS to perform
stream operations like mute and gain control.
REQ-MCP-17 - The AS shall be able to instruct the MS to play a
specific announcement.
REQ-MCP-18 - The AS shall be able to request the MS to create,
delete, and manipulate a mixing, IVR, or announcement session.
REQ-MCP-19 - The AS shall be able to instruct the MS to play
announcements to a single user or to a conference mix.
REQ-MCP-20 - The MS control protocol should enable the AS to ask the
MS for a session summary report. The report may include resource
usage and quality metrics.
REQ-MCP-21 - The MS shall be able to notify the AS of events
received in the media stream if requested by the AS. (Examples -
STUN request, Flow Control, etc.)
3.2. Media mixing Requirements
REQ-MCP-22 - The AS shall be able to define a conference mix; the MS
may offer different mixing topologies. The conference mix may be
defined on a conference or user level.
REQ-MCP-23 - The AS may be able to define a custom video layout
built of rectangular sub-windows.
REQ-MCP-24 - For video, the AS shall be able to map a stream to a
specific sub-window or to define to the MS how to decide which
stream will go to each sub-window.
REQ-MCP-25 - The MS shall be able to notify the ASs of who the
active sources of the media are; for example, who the active
speaker is or who is being viewed in a conference. The speaker
and the video source may be different, for example, a person
describing a video stream from a remote camera managed by a
different user.
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REQ-MCP-26 - The MS shall be able to inform the AS which layouts it
supports.
REQ-MCP-27 - The MS control protocol should enable the AS to
instruct the MS to record a specific conference mix.
3.3. IVR Requirements
REQ-MCP-28 - The AS shall be able to instruct the MS to perform one
or more IVR scripts and receive the results. The script may be in
a server or contained in the control message.
REQ-MCP-29 - The AS shall be able to manage the IVR session by
sending requests to play announcements to the MS and receiving the
response (e.g., DTMF). The IVR session flow, in this case, is
handled by the AS by starting a next phase based on the response
it receives from the MS on the current phase.
REQ-MCP-30 - The AS should be able to instruct the MS to record a
short participant stream and play it back. This is not a
recording requirement.
3.4. Operational Requirements
These requirements may be applicable to the MRB, but they can be used
by an AS if it has a one-to-one connection to the MS.
REQ-MCP-31 - The MS control protocol must allow the AS to audit the
MS state during an active session.
REQ-MCP-32 - The MS shall be able to inform the AS about its status
during an active session.
4. Security Considerations
This document discusses high-level requirements for MCP. The MCP has
some specific security requirements, which will be summarized here at
a very high level.
All of the operations and functions described in this document need
to be authorized by an MS or an AS. It is expected that MS resources
will be governed by a set of authorization rules defined as part of
the AS / MS policy. In order for the policy to be implemented, the
MS needs to be able to authenticate requests. Normal SIP mechanisms,
including Digest authentication and certificates, can be used as
specified in RFC 3261 [RFC3261]. These MCP security requirements
will be discussed in detail in the framework and protocol documents.
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5. Acknowledgments
This RFC represents the work from two previous personal works in
progress, "Media Control Protocol Requirements" and "Requirements for
a Media Server Control Protocol". The authors would like to
acknowledge the work of Gary Munson from AT&T Labs, and James
Rafferty from Cantata who helped write "Media Control Protocol
Requirements", on which this work is based.
6. Informative References
[CARCH] Rosenberg, J., "A Framework for Conferencing with the
Session Initiation Protocol (SIP)", RFC 4353,
February 2006.
[MEDIACTRL-FW] Melanchuk, T., Ed., "An Architectural Framework for
Media Server Control", Work in Progress,
February 2008.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G.,
Johnston, A., Peterson, J., Sparks, R., Handley, M.,
and E. Schooler, "SIP: Session Initiation Protocol",
RFC 3261, June 2002.
[XCON-FRMWRK] Barnes, M., Boulton, C., and O. Levin, "A Framework
for Centralized Conferencing", Work in Progress,
November 2007.
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Authors' Addresses
Martin Dolly
AT&T Labs
200 Laurel Avenue
Middletown, NJ 07748
USA
Phone:
EMail: mdolly@att.com
URI:
Roni Even
Polycom
94 Derech Em Hamoshavot
Petach Tikva 49130
Israel
EMail: roni.even@polycom.co.il
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