Internet DRAFT - draft-bergren-mmusic-rtsp-ermi-extensions
draft-bergren-mmusic-rtsp-ermi-extensions
Network Working Group C. Bergren
Internet-Draft J-F. Mule, Ed.
Intended status: Informational CableLabs
Expires: August 21, 2008 February 18, 2008
Extensions to RTSP based on the CableLabs Edge Resource Management
Interface Specification (ERMI)
draft-bergren-mmusic-rtsp-ermi-extensions-00
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Copyright (C) The IETF Trust (2008).
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Abstract
This document provides a description of the RTSP extensions used in
the CableLabs Edge Resource Manager Interface specification. It is
provided as an informational note based on a recent liaison statement
received by CableLabs from the IETF MMUSIC working group.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. ERMI extensions to RTSP . . . . . . . . . . . . . . . . . . . 6
2.1. List of ERMI extensions . . . . . . . . . . . . . . . . . 6
2.2. Limited Applicability of RTSP ERMI extensions . . . . . . 7
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
7. Informative References . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
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1. Introduction
In 2004-2005, work was initiated on a Modular Cable Modem Termination
System (M-CMTS) architecture at CableLabs. A number of
specifications were published including the Edge Resource Manager
Interface Specification [ERMI].
A block diagram of the architecture relevant to the ERMI
specification and its use of the RTSP protocol is shown on Figure 1.
DOCSIS stands for Data-Over-Cable-Service-Interface Specifications.
The cable head-end architecture centers on DOCSIS CMTS systems that
send Video and Internet data to subscribers.
An Edge QAM (EQAM) is a head-end or hub device that receives packets
of digital video or data from the operator network. It re-packetizes
the video or data into an MPEG transport stream and digitally
modulates the transport stream onto a downstream RF carrier using
Quadrature Amplitude Modulation (QAM).
A CMTS requires resources (such as EQAMs) to relay this data to
subscriber modems. These resources are allocated by an Edge Resource
Manager (ERM).
The CMTS and EQAMs use the Real-Time Streaming Protocol (RTSP,
[RFC2326]), as defined in section 5.2.3. of the CableLabs Edge
Resource Manager Interface Specification ([ERMI]) during the resource
allocation process. The CMTS asks the Edge Resource Manager for an
EQAM, the ERM confers with the EQAMs, and then gives the CMTS the
appropriate EQAM resource.
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+------------+ +-------------------------+
| +------+ | |+------+ Edge Resource |
| |RTSP <-+-->+RTSP | Manager |
| |Client| | ||Server| +-----------+ |
| +------+ | |+------+ |RTSP Client| |
| | | +-------^---+ |
| | +-------------------|-----+
| | |
| | |
| Modular | |
| Cable | EQAMs |
| Modem | +------------+ |
| Termination| | +------------- |
| System | | | +---------- | -+
| Core | | | | +---------|--------+
| | +-| | | +------v----+ | +-------+
| (M-CMTS | +--| | |RTSP Server| | | Cable |
| Core) | +-| +-----------+ | | Modem |
| | DATA | | | |
==|========================-+-=================+-|=======|==>>
| | +------------------+ +-------+
| |
+------------+
RTSP Usage in Edge Resource Manager Interface Specification
Figure 1
The M-CMTS core, the ERM, and the EQAM use TCP as the transport-layer
protocol and listen on TCP port 554 for incoming RTSP connections.
The M-CMTS core acts as an RTSP client. The ERM plays the role of an
RTSP client and an RTSP server. The EQAM acts as an RTSP server.
The RTSP SETUP, TEARDOWN, PING and GET PARAMETER methods must at a
minimum be supported by M-CMTS, ERM and EQAM. In addition, the
M-CMTS core and the ERM must also support the ANNOUNCE method.
A session keepalive method named PING has been added as part of the
ERMI specification. The authors note that the OPTIONS method could
have been used to act as a PING mechanism as it is the case with some
SIP implementations.
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PING rtsp://172.22.10.3 RTSP/1.0
CSeq: 123
Session: 1234567
Require: ermi
A corresponding response from the RTSP server to the client:
RTSP/1.0 200 OK
CSeq: 123
Session: 1234567
The ERMI specification makes extensions to RTSP [RFC2326] to add
EQAM-specific parameters; the applicability of ERMI messages is
within the internal system architecture of a DOCSIS M-CMTS system and
within a DOCSIS cable network. These extensions are briefly
discussed Section 2.1.
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2. ERMI extensions to RTSP
2.1. List of ERMI extensions
Section 7.1.5 "RTSP Extensions" of the [ERMI] specification outlines
the relevant extensions. These extensions are briefly summarized
here; the specification should be examined directly for more details.
The following extensions to RTSP have been used in ERMI:
o New parameters for the Transport header:
Section 12.39 of [RFC2326] specifies the Transport header. ERMI
Extensions to the Transport header identify parameters
associated with the transport of the media stream through an
EQAM.
Transport headers take the form of:
Transport: <channel> [, <channel>].
Each <channel> field takes the form: DOCSIS/QAM; unicast. The
bit rate, QAM ID and DEPI mode are passed as part of the
transport header with additional optional values.
o New DOCSIS-Notice header:
The DOCSIS-Notice header header provides information sent from
an RTSP server to a client in an ANNOUNCE request, specifically
to reclaim an ERMI session.
The syntax of the DOCSIS-Notice header is:
DOCSIS-Notice: <notice-code>
The RTSP client and server must support the values of notice-
code and code-description defined in the ERMI specification.
Currently, only the value of '5701' is define to reclaim a
session.
o New RTSP option tag in the Require header:
The Require: header must be present in RTSP requests methods,
with the newly defined 'ermi' tag (see IANA consideration
section).
o New parameters for GET_PARAMETER method:
The RTSP GET_PARAMETER method is used by the client to obtain
the list of active RTSP sessions that were initiated by the
client before the current TCP connection was established. It is
used by a client as a mechanism to synchronize its session state
with the RTSP server following a client reboot.
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2.2. Limited Applicability of RTSP ERMI extensions
There are several considerations to the ERMI RTSP extensions.
First, the ERMI specification is intended to be used within a single
cable administrative domain, a 'closed' cable system head-end with
controlled network and administrative domains. It is unlikely that
the [ERMI] protocols will escape these domains as the ERMI traffic is
considered as a service control and management.
Secondly, the ERMI specification requires that RTSP requests include
the Require Header with the 'ermi' option tag. Section 12.32 of
[RFC2326] requires a non-ERMI server to reject this ERMI option tag
header as Unsupported.
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3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
This document also reuses the terminology defined in [ERMI] and it is
recommended for the reader to read the ERMI specification.
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4. IANA Considerations
The CableLabs ERMI specification currently makes use of a new option
tag indicating support for the ERMI RTSP requirements; this option
tag means that the various extensions (PING Method, Transport header,
etc.) are supported.
Depending on the feedback from the IETF MMUSIC working group, this
section should properly register the extensions that are deemed
necessary.
For example, a new option tag should be defined as described in
section 3.8.1 of [RFC2326]:
o Name and description of option:
The name of this new option is 'ermi' (or may be
com.cablelabs.ermi). This text should explicitly define what is
required to be supposed to claim compliance with this new option
tag.
o Change of control: CableLabs?
o Reference: [ERMI]
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5. Security Considerations
This section is left for further study.
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6. Acknowledgments
This IETF Internet-Draft document provides some high-level
information and pointers to the RTSP extensions used in the CableLabs
ERMI specification published by CableLabs as part of the Modular
Cable Modem Termination System (M-CMTS) architecture.
The following individuals are acknowledged in the CableLabs ERMI
document as the main contributors:
Charles Bergren and Eduardo Cardona of CableLabs, Doc Evans of ARRIS
International, Inc., Xiaomei Liu of Cisco Systems, Inc., Michael
Mercurio of Camiant, Mike Patrick of Motorola, Sangeeta Ramkrishnan
of Cisco Systems, Inc., Dan Smith of BigBand Networks, and Bruce
Thompson of Cisco Systems, Inc.
In particular, Xiaomei Liu and Doc Evans contributed extensively by
serving as lead authors for the ERMI specification. We thank Dan
Smith, Mike Patrick and Michael Mercurio who provided valuable
thoughts and text. We would also like to acknowledge Bruce Thompson
and Sangeeta Ramkrishnan for their work on the initial text. We
thank Charles Bergren and Eduardo Cardona, who were the ERMI team
leads. And finally many thanks go out to all the active cable
operator participants, members of the CableLabs who contributed to
the ERMI specification.
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7. Informative References
[ERMI] CableLabs, "Edge Resource Manager Interface Specification,
CM-SP-ERMI-I02-051209", CableLabs Specification http://
www.cablelabs.com/specifications/
CM-SP-ERMI-I02-051209.pdf, February 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
Streaming Protocol (RTSP)", RFC 2326, April 1998.
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Authors' Addresses
Charles Bergren
CableLabs
858 Coal Creek Circle
Louisville, CO 80027
USA
Email: c.bergren@cablelabs.com
Jean-Francois Mule
CableLabs
858 Coal Creek Circle
Louisville, CO 80027
USA
Email: jfm@cablelabs.com
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