Network Working Group L. Dondeti, Ed.
Internet-Draft QUALCOMM, Inc.
Intended status: Informational A. Jerichow
Expires: August 5, 2007 Nokia Siemens Networks GmbH and
Co.KG
February 2007
SDP Attributes for OMA BCAST Service and Content Protection
draft-dondeti-oma-sip-sdp-attrs-01
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Abstract
This document provides descriptions of SDP attributes used by the
Open Mobile Alliance's Broadcast Service and Content Protection
specification.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. New SDP Attributes . . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 7
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1. Introduction
The Open Mobile Alliance (OMA)'s Broadcast (BCAST) group is
specifying service and content protection mechanisms for broadcast
services over wireless networks. As part of that specification,
several new SDP attributes are necessary to allow the broadcast
server to signal the service and content protection parameters to
clients.
Section 8.2.4 of RFC 4566 [1] requires that new SDP attributes are
registered through IANA with name, contact information and
description (and other similar parameters). A standards track
specification is RECOMMENDED if the new attribute(s) will have
widespread use and interoperability considerations.
OMA BCAST specifications are expected to be used by 3GPP MBMS, 3GPP2
BCMCS and DVB-H based broadcast wireless systems. Whereas that might
qualify as widespread use, all of the networks compliant to those
specifications will use the OMA specification as the point of
reference for interoperability and inter-operation. Thus, it may be
sufficient to simply document the attributes and the context in which
they are used.
This document provides descriptions of the SDP attributes used in the
OMA BCAST Service and Content Protection specification.
2. 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 RFC 2119 [2].
3. New SDP Attributes
The following new SDP attributes have been specified:
a=bcastversion:<major>.<minor>
This field specifies the OMA BCAST version "bcastversion" Value in
the format x.y. The Value field is of XML data type Decimal.
This is a session-level attribute and is not dependent on charset.
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a=keystreamtype:<Type of Keystream>
This field specifies the type of keystream as a string. The valid
values are "stkm" and "ltkm" for short and long term key messages.
This is a session or a media-level attribute and is not dependent
on charset.
a=stkmstream:<id of the stkm stream>
The stkmstream attribute specifies mapping Short Term Key Message
(STKM) streams to media streams in the SDP.
The attribute can be at session level, in which case it applies to
all media streams, or it can be at media level, in which case it
only applies to the specified media and would overwrite possible
session level attribute.
Each session or media stream can have multiple stkmstream
attributes. Using this attribute, the terminal can lookup the
corresponding STKM stream announcements and figure out which one
to listen to and process. We note that this attribute is optional
and hence would not be there for unencrypted media streams.
This field is not dependent on charset.
a=encryptedstreamid:<id of the stkm stream>
This field refers to the encrypted stream id and takes a non-zero
positive integer. This is a session or a media-level attribute
and is not dependent on charset.
a=SRTPAuthentication:<id for SRTP authentication algorithm value>
When SRTP is used, the attribute SRTPAuthentication states which
authentication algorithm to use. Based on RFC4771, the identifier
is a transform-independent parameter of the cryptographic context
for SRTP in integer format.
One of the following three integrity transforms registered for the
three modes MUST be used: value "2" for RCCm1, "3" for RCCm2 and
"4" for RCCm3.
a=SRTPROCTxRate:<ROC transmission rate>
When SRTP is used, the attribute SRTPROCTxRate is used to define
the ROC transmission rate, R, which is given in network byte
order.
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R MUST be a non-zero unsigned integer between 1 and 65535
inclusive, as specified in [RFC4771]. If the ROC transmission
rate is not included in the negotiation, the default value of 1
SHALL be used.
4. Security Considerations
In addition to the notes in Section 7 of RFC 4566 [1], the following
considerations may be applicable:
Some of the new SDP parameters indicate the version, type of the key
management system used for service or content protection of broadcast
content. Others provide references to relevant key management
traffic streams so that receivers can map the media streams to key
streams and retrieve the necessary keys to decrypt media.
Modification of references to key streams will result in DoS attacks,
but nothing more. However, if the kmsversion parameter is sent
unprotected, there may be possibilities for downgrade attacks.
5. IANA Considerations
This specification requests registration of the following SDP
attributes:
o a=bcastversion:<major>.<minor>
o a=keystreamtype:<Type of Keystream>
o a=stkmstream:<id of the stkm stream>
o a=encryptedstreamid:<id of the stkm stream>
o a=SRTPAuthentication:<id for SRTP authentication algorithm value>
o a=SRTPROCTxRate:<ROC transmission rate>
6. Acknowledgments
Many thanks to Charles Lo, Uwe Rauschenbach, David Castleford and
Hosame Abu-Amara for their help and support.
7. References
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7.1. Normative References
[1] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K.
Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830,
August 2004.
[4] Carrara, E., Lehtovirta, V., and K. Norrman, "The Key ID
Information Type for the General Extension Payload in Multimedia
Internet KEYing (MIKEY)", RFC 4563, June 2006.
[5] Open Mobile Alliance, "Service and Content Protection for Mobile
Broadcast Services", OMA TS-BCAST-SvcCntProtection-V1_0-
20060412-D, 2006.
7.2. Informative References
[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
Authors' Addresses
Lakshminath Dondeti (editor)
QUALCOMM, Inc.
5775 Morehouse Dr
San Diego, CA
USA
Phone: +1 858-845-1267
Email: ldondeti@qualcomm.com
Anja Jerichow
Nokia Siemens Networks GmbH and Co.KG
81730 Munich,
Germany
Phone: +49 89 636-45868
Email: anja.jerichow@nsn.com
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