Network Working Group C. Boulton
Internet-Draft Avaya
Intended status: Standards Track R. Even
Expires: May 22, 2008 Polycom
November 19, 2007
Media Resource Brokering
draft-boulton-mediactrl-mrb-01
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Abstract
The MediaCtrl work group in the IETF is currently proposing an
architecture for controlling media services. The Session Initiation
Protocol will be used as the signalling protocol which provides many
inherent capabilities for message routing. In addition to such
signalling properties, a need exists for intelligent, application
level media service selection based on non-static signalling
properties. This is especially true when considered in conjunction
with deployment architectures that include 1:M and M:M combinations
of Application Servers and Media Servers.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 6
3. Problem Discussion . . . . . . . . . . . . . . . . . . . . . . 7
4. Deployment Scenario Options . . . . . . . . . . . . . . . . . 8
4.1. Query MRB . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.1. Hybrid Query MRB . . . . . . . . . . . . . . . . . . . 9
4.2. In-Line MRB . . . . . . . . . . . . . . . . . . . . . . . 10
5. Interface Discussion . . . . . . . . . . . . . . . . . . . . . 12
5.1. Media Server Resource Publishing Interface . . . . . . . . 12
5.2. Media Service Resource Consumer Interface . . . . . . . . 12
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8. Normative References . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . . . 18
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1. Introduction
The topic of Media Resources has been in discussion for a number of
years with varying proprietary solutions being used. It is clear
that as we move towards a consistent architecture and protocol for
Media Server Control, a standard mechanism is required for accurate
media resource location.
As IP based telecom infrastructures mature, the complexity and
demands from deployments increase. Such complexity will result in a
wide variety of capabilities from a range of vendors that should all
be interoperable using the architecture and protocols produced by the
MediaCtrl work group. It should be possible for a controlling entity
to be assisted in Media Server selection so that the most appropriate
resource is selected for a particular operation. The importance
increases when you introduce a flexible level of deployment
scenarios, as specified in the MediaCtrl requirements[ref]. This
document states that "it should be possible to have a many-to-many
relationship between Application Servers and Media Servers that use
this protocol". This leads to the following deployment architectures
being possible when considering media resources.
The simplest deployment view is illustrated in Figure 1.
+---+-----+---+ +---+-----+---+
| Application | | Media |
| Server |<-------MS Control------>| Server |
+-------------+ +-------------+
Figure 1: Basic Architecture
This simply involves a single Application Server and Media Server.
Expanding on this view, it is also possible for an Application Server
to be controlling multiple (greater that 1) Media Servers. This
deployment view is illustrated in Figure 2. Typically, such
architectures are associated with application logic that requires
high demand media services. It is more than possible that each media
server possesses a different media capability set. Media servers may
offer different media services as specified in the Mediactrl
architecture document. A Media server may have similar media
functionality but may have different capacity or media codec support.
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+---+-----+---+
| Media |
+----->| Server |
| +-------------+
|
+---+-----+---+ | +---+-----+---+
| Application | | | Media |
| Server |<--MS Control-----+----->| Server |
+-------------+ | +-------------+
|
| +---+-----+---+
+----->| Media |
| Server |
+-------------+
Figure 2: Basic Architecture
Figure 3 conveys the opposite view to that in Figure 2. In this
model there are a number of (greater than 1) application servers
controlling a single media server. Typically, such architectures are
associated with application logic that requires low demand media
services.
+---+-----+---+
| Application |
| Server |<-----+
+-------------+ |
|
+---+-----+---+ | +---+-----+---+
| Application | | | Media |
| Server |<-----+-----MS Control-->| Server |
+-------------+ | +-------------+
|
+---+-----+---+ |
| Application | |
| Server |<-----+
+-------------+
Figure 3: Basic Architecture
The final deployment view is the most complex. In this model (M:M)
there exists any number of Application Servers and any number of
Media Servers. It is again possible in this model that media servers
might not be homogenous and have different capability sets.
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+---+-----+---+ +---+-----+---+
| Application | | Media |
| Server |<-----+ +---->| Server |
+-------------+ | | +-------------+
| |
+---+-----+---+ | | +---+-----+---+
| Application | | | | Media |
| Server |<-----+-MS Control-+---->| Server |
+-------------+ | | +-------------+
| |
+---+-----+---+ | | +---+-----+---+
| Application | | +---->| Media |
| Server |<-----+ | Server |
+-------------+ +---+-----+---+
Figure 4: Basic Architecture
This document will take a look at the specific problem areas related
to such deployment architectures and some potential solutions.
Finally some proposed Interface solutions will be looked at in more
detail.
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2. Conventions and Terminology
In this document, BCP 14/RFC 2119 [RFC2119] defines the key words
"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL". In addition, BCP 15 indicates requirement levels for
compliant implementations.
This document inherits terminology proposed in the MediaCtrl
Framework [ref]. In addition, The following terms are defined for
use in this document and for use in the context of the MediaCtrl Work
group in the IETF:
Media Resource Broker (MRB) A logical entity that is responsible for
both collection of appropriate published Media Server (MS)
information and supplying of appropriate MS information to
consuming entities.
Query MRB An instantiation of an MRB (See previous definition) that
provides an interface for an Application Server to retrieve the
location of an appropriate Media Server. The result returned to
the Application Server can be influenced by information contained
in the query request.
In-line MRB An instantiation of an MRB (See definition) that
directly receives requests on the signalling path. The decision
making process is totally delegated to the MRB.
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3. Problem Discussion
It is clear from Section 1 that the MediaCtrl group will be producing
a solution that must service a wide variety of deployment
architectures. These range from the simplest 1:1 relationship
between Media Servers and Application Servers to potentially linearly
scaling 1:M, M:1 and M:M deployments.
This still does not seem like a major issue for the proposed solution
until you add a number of additional factors into the equation that
increase complexity. As Media Servers evolve it must be taken into
consideration that where many can exist in a deployment, they may not
have been produced by the same vendor and may not have the same
capability set. It should be possible for an Application Server that
exists in a deployment to select a Media Service based on an
appropriate capability set. In conjunction with capabilities, it is
also important to take available resources into consideration. The
ability to select an appropriate Media Service function is an
extremely useful feature but becomes even more powerful when
considered in conjunction with available resources for servicing a
request.
In conclusion, the intention is to create a tool set that allows
MediaCtrl deployments to effectively utilize the available media
resources. It should be noted that in the simplest deployments where
only a single media server exists, an MRB function is probably not
required. Only a single capability set exists and resource
unavailability can be handled using the appropriate underlying
signalling e.g. SIP response.
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4. Deployment Scenario Options
On researching Media Resource Brokering it became clear that a couple
of high level models exist. The general principles of "in-line" and
"query" MRB concepts are discussed in the rest of this section.
4.1. Query MRB
The "Query" model for MRB interactions provides the ability for a
client of media services (for example an Application Server) to "ask"
an MRB for an appropriate Media Server, as illustrated in Figure 5.
+---+-----+---+
+------------>| MRB |<----------+----<-----+---+
| +-------------+ (1)| | |
| | | |
|(2) +---+--+--+---+ | |
| | Media | | |
| +---->| Server | | |
| | +-------------+ | |
| | (1)| |
+---+--+--+---+ | +---+-----+---+ | |
| Application | | | Media | | |
| Server |<-----+-MS Control-+---->| Server |->-+ |
+-------------+ (3) | +-------------+ |
| |
| +---+-----+---+ (1)|
+---->| Media | |
| Server |--->---+
+---+-----+---+
Figure 5: Query MRB
In this deployment, the Media Servers use the "Media Server Resource
Publishing Interface", as discussed in Section 5.1, to convey
capability sets as well as resource information. This is depicted by
(1) in Figure 5. It is then the MRB's responsibility to accumulate
all appropriate information relating to media services in the logical
deployment cluster. The Application Server (or other media services
client) is then able to query the MRB for an appropriate resource (as
identified by (2) in Figure 5). Such a query would carry specific
information related to the Media Service required and enable the MRB
to provide an increased accuracy in its response. This particular
interface is discussed in "Media Resource Consumer Interface" in
Section 5.2. The Application Server is then able to direct control
commands (for example create conference) and Media Dialogs to the
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appropriate Media Server, as shown by (3) in Figure 5.
4.1.1. Hybrid Query MRB
As mentioned previously, it is the intention that a tool kit is
provided for MRB functionality within a MediaCtrl architecture. It
is expected that in specific deployment scenarios the role of the MRB
might be co-hosted as a hybrid logical entity with an Application
Server, as shown in Figure 6.
+------------<----------------<---------+----<-----+---+
| (1) | | |
| | | |
| +---+--+--+---+ | |
| | Media | | |
V +---->| Server | | |
+------+------+ | +-------------+ | |
| MRB | | | |
+---+--+--+---+ | +---+-----+---+ | |
| Application | | | Media | | |
| Server |<-----+-MS Control-+---->| Server |->-+ |
+-------------+ | +-------------+ |
| |
| +---+-----+---+ |
+---->| Media | |
| Server |--->---+
+---+-----+---+
Figure 6: Hybrid Query MRB - AS Hosted
This diagram is identical to that in Figure 5 with the exception that
the MRB is now hosted on the Application Server. The "Media Server
Publishing Interface" is still being used to accumulate resource
information at the MRB but as it is co-hosted on the Application
Server, the "Media Server Consumer Interface" has collapsed. It
might still exist within the Application Server/MRB interaction but
this is an implementation issue. This type of deployment suits a
single Application Server environment but it should be noted that a
"Media Server Consumer Interface" could then be offered from the
hybrid if required.
In a similar manner, the Media Server could also act as a hybrid for
the deployment cluster, as illustrated in Figure 7.
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(1) +---+-----+---+
+---+---+------------->---------------->----------->| MRB |
| | | +---+--+--+---+ +---+-----+---+
| | +-<-| Application | | Media |
| | | Server |<--+-MS Control-+------->| Server |
| | +-------------+ | +-------------+
| | |
| | +---+--+--+---+ |
| +---<---| Application | |
| | Server |<--+-MS Control-+--+
| +-------------+ |
| |
| +---+--+--+---+ |
+---<-------| Application | |
| Server |<--+-MS Control-+--+
+-------------+
Figure 7: Hybrid Query MRB - MS Hosted
This time the MRB has collapsed and is co-hosted by the Media Server.
The "Media Server Consumer Interface" is still available to the
Application Servers (1) to query Media Server resources. This time
the "Media Server Publishing Interface" has collapsed onto the Media
Server. It might still exist within the Media Server/MRB interaction
but this is an implementation issue. This type of deployment suits a
single Media Server environment but it should be noted that a "Media
Server Publishing Interface" could then be offered from the hybrid if
required.
4.2. In-Line MRB
The "In-line" MRB has a subtle difference from the "Query" model that
was discussed in the previous section. The Concept of a "Media
Server Consumer Interface" disappears. The client of the MRB simply
uses the signalling to offload the decision making process - this
applies to both media server Control and Media Dialogs. This type of
deployment is illustrated in Figure 8.
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+-------<----------+----<-------+---+
| | (1) | |
| | | |
| +---+--+--+---+ | |
| | Media | | |
| +------>| Server | | |
| |(3) +-------------+ | |
| | (1)| |
+---+--+--+---+ | | +---+-----+---+ | |
| Application | (2) +---+--V--+---+ (3) | Media | | |
| Server |----->| MRB |----->| Server |->-+ |
+-------------+ +---+-----+---+ +-------------+ |
| |
| (3) +---+-----+---+ (1)|
+------>| Media | |
| Server |--->---+
+---+-----+---+
Figure 8: In-line MRB
The Media Servers still use the 'Media Server Publishing Interface'
to convey capabilities and resources to the MRB - as illustrated by
(1). The media server Control and Media dialogs are blindly sent to
the MRB (2) which then selects an appropriate Media Server (3). The
result of such an architecture is that the decision is left entirely
to the MRB and the Application Server has no input into the selection
process. This is the opposite to the "Query" model which provided
information that would help influence the Media Server decision
making process on the application server. As a by-product of this
decision shift, a lot more emphasis is placed on the intelligence of
the MRB. It will actually have to inspect both the SIP signalling
and the media server control protocol PDUs for the purpose of Media
Server selection. This includes, for example, looking for explicit
capabilities in the signalling and session details such as media
types, codecs and bandwidth requirements. Ultimately the decision
making and policy enforcement is removed from the Application Server
and shifted to the MRB logical entity.
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5. Interface Discussion
As discussed in previous sections in this document, the intention is
to provide a toolkit for a variety of architectures where media
resource brokering can take place. As a result, two main interfaces
are required to support the differing requirements. The two
interfaces are described in the remainder of this section and have
been named the 'Media Server Resource Publishing' and Media Server
Resource Consumer' interfaces. These two interfaces have extremely
differing responsibilities and usages which is reflected in the
choice of solutions.
It is beyond the scope of this document to define exactly how to
construct an MRB. This includes interpreting the data for the Media
Service Consumer interface supplied by the Media Serer Publishing
interface. It is, however, important that the two interfaces are
complimentary so that development of appropriate MRB functionality is
supported.
5.1. Media Server Resource Publishing Interface
The Media Server Resource Publishing interface is responsible for
providing an MRB with appropriate Media Server resource information.
It is generally accepted that this interface provides both general
and specific details related to Media Server resources. This
information needs to be conveyed using an industry standard mechanism
to provide increased levels of adoption and interoperability. The
Simple Network Management Protocol (SNMP) will provide the basis for
the interface.
An overview of the documents of the Internet-Standard Management
Framework is provided in section 7 of RFC 3410 [RFC3410]. This
interface will provide Management Information Base (MIB) objects that
are accessed through the Simple Network Management Protocol (SNMP).
Objects contained within the Media Server publishing interface are
defined using Structure of Management Information (SMI). The Media
Server publishing MIB will be compliant to SMIv2, which is defined in
RFC 2578 [RFC2578], RFC 2579 [RFC2579] and RFC 2580 [RFC2578].
EDITORS NOTE: Need to map resources to MIB and define appropriately.
5.2. Media Service Resource Consumer Interface
The Media Server Consumer interface provides the ability for clients
of an MRB, such as Application Servers, to request an appropriate
Media Server to satisfy specific criteria. The interface allows a
client to pass detailed meta-information to the MRB to help select an
appropriate Media Server. The MRB is then able to make and informed
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decision and provide the client with an appropriate media server
resource.
The interface is therefore based on a client-server Remote Procedure
Call mechanism, with the Simple Object Access Protocol (SOAP)
[W3C.REC-soap12-part1-20030624] [W3C.REC-soap12-part2-20030624] used
to carry out the interactions. The data structures will be defined
using the Web Services Description Language (WSDL)
[W3C.CR-wsdl20-20051215] definition and XML schema.
EDITORS NOTE: Need to map appropriate RPC to WSDL and define
appropriately.
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6. Acknowledgments
The authors would like to thank
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7. Security Considerations
Security Considerations to be included in later versions of this
document.
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8. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Textual Conventions for SMIv2",
STD 58, RFC 2579, April 1999.
[RFC2580] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
"Conformance Statements for SMIv2", STD 58, RFC 2580,
April 1999.
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
[W3C.CR-wsdl20-20051215]
Chinnici, R., Moreau, J., Ryman, A., and S. Weerawarana,
"Web Services Description Language (WSDL) Version 2.0 Part
1: Core Language", W3C CR CR-wsdl20-20051215,
December 2005.
[W3C.REC-soap12-part1-20030624]
Gudgin, M., Moreau, J., Mendelsohn, N., Hadley, M., and H.
Nielsen, "SOAP Version 1.2 Part 1: Messaging Framework",
World Wide Web Consortium FirstEdition REC-soap12-part1-
20030624, June 2003,
<http://www.w3.org/TR/2003/REC-soap12-part1-20030624>.
[W3C.REC-soap12-part2-20030624]
Mendelsohn, N., Gudgin, M., Hadley, M., Nielsen, H., and
J. Moreau, "SOAP Version 1.2 Part 2: Adjuncts", World Wide
Web Consortium FirstEdition REC-soap12-part2-20030624,
June 2003,
<http://www.w3.org/TR/2003/REC-soap12-part2-20030624>.
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Authors' Addresses
Chris Boulton
Avaya
Building 3
Wern Fawr Lane
St Mellons
Cardiff, South Wales CF3 5EA
Email: cboulton@avaya.com
Roni Even
Polycom
94 Derech Em Hamoshavot
Petach Tikva 49130, Israel
Email: roni.even@polycom.co.il
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