One document matched: draft-ietf-avt-profile-savpf-00.txt
INTERNET-DRAFT Joerg Ott/Uni Bremen TZI
draft-ietf-avt-profile-savpf-00.txt Elisabetta Carrara/Ericsson
19 October 2003
Expires March 2004
Extended Secure RTP Profile for RTCP-based Feedback (RTP/SAVPF)
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF),
its areas, and its working groups. Note that other groups may also
distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet- Drafts
as reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
An RTP profile (SAVP) is defined for secure real-time
communications, and another profile (AVPF) is specified to provide
timely feedback from the receivers to a sender. This memo defines
the combination of both profiles to enable secure RTP
communications with feedback.
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Table of Contents
1 Introduction.................................................2
1.1 Definitions.............................................3
1.2 Terminology.............................................4
2 SAVPF Rules..................................................4
2.1 Packet Formats..........................................5
2.2 Extensions..............................................5
2.3 Implications from combining AVPF and SAVP...............5
3 SDP Definitions..............................................6
3.1 Profile Definition......................................6
3.2 Attribute Definitions...................................6
3.3 Profile Negotiation.....................................6
3.3.1 Offer/Answer-based Negotiation of Session Descriptions.7
3.3.2 RTSP-based Negotiation of Session Descriptions.........7
3.3.3 Announcing Session Descriptions........................7
3.3.4 Describing Alternative Session Profiles................8
3.4 Examples................................................9
4 Interworking of AVP, SAVP, AVPF, and SAVPF Entities.........11
5 Security Considerations.....................................11
6 IANA Considerations.........................................12
7 Acknowledgements............................................13
8 Authors' Addresses..........................................13
9 Bibliography................................................13
9.1 Normative references...................................14
9.2 Informative References.................................14
10 IPR Notice..................................................15
11 Full Copyright Statement....................................15
1 Introduction
The Real-time Transport Protocol (RTP/RTCP) [1] and the associated
profile for audiovisual communications with minimal control [2]
define mechanisms for transmitting time-based media across an IP
network. RTP provides means to preserve timing and detect packet
losses, among other things, and RTP payload formats provide for
proper framing of (continuous) media in a packet-based environment.
RTCP enables receivers to provide feedback on reception quality and
allows all members of an RTP session to learn about each other.
The RTP specification provides only rudimentary support for
encrypting RTP and RTCP packets. SRTP [4] defines an RTP profile
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("SAVP") for secure RTP media sessions, defining methods for proper
RTP and RTCP packet encryption, integrity and replay protection.
The initial negotiation of SRTP and its security parameters needs
to be done out of band, using e.g. the Session Description Protocol
(SDP) [6] together with extensions for conveying keying material
[7][8].
The RTP specification also provides limited support for timely
feedback from receivers to senders, typically by means of reception
statistics reporting in somewhat regular intervals depending on the
group size, the average RTCP packet size, and the available RTCP
bandwidth. The extended RTP profile for RTCP-based feedback
("AVPF") [3] allows receivers statistically to provide immediate
feedback while maintaining the average RTCP data rate for all
senders. As for SAVP, the use of AVPF and its parameters need to
be negotiated out-of-band by means of SDP [6] and the extensions
defined in [3].
Both SRTP and AVPF are RTP profiles and need to be negotiated.
This implies that either one or the other may be used, but both
profiles cannot be negotiated for the same RTP session (using one
SDP session level description). However, using secure
communications and timely feedback together is desirable.
Therefore, this document specifies a new RTP profile ("SAVPF") that
combines the features of SAVP and AVPF.
As SAVP and AVPF are largely orthogonal, the combination of both is
mostly straightforward. No sophisticated algorithms need to be
specified in this document. Instead, reference is made to both
existing profiles and only the implications of their combination
and possible deviations from rules of the existing profiles are
described as is the negotiation process.
1.1 Definitions
The definitions of [1], [2], [3], and [4] apply.
The following definitions are specifically used in this document:
RTP session:
An association among a set of participants communicating with
RTP as defined in [1].
(SDP) media description:
This term refers to the specification given in a single m=
line in an SDP message. An SDP media description may define
only one RTP session. Grouping of m= lines in SDP may cause
several SDP session level descriptions to define (alternatives
of) the same RTP session for the same media type.
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Media session:
A media session refers to a collection of SDP media
descriptions that are semantically grouped to represent
alternatives of the same communications means. Out of such a
group, one will be negotiated or chosen for a communication
relationship and the corresponding RTP session will be
instantiated. Or the media session will be rejected.
In the simplest case, a media session is equivalent to an SDP
media description and equivalent to an RTP session.
1.2 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
[5].
2 SAVPF Rules
SAVP is defined as an intermediate layer between RTP (following the
regular RTP profile AVP) and UDP. This yields a two layer
hierarchy within the Real-time Transport Protocol. In SAVPF, the
upper (AVP) layer is replaced by the extended RTP profile for
feedback (AVPF).
AVPF modifies timing rules for transmitting RTCP packets and adds
extra RTCP packet formats specific to feedback. These functions
are independent of whether or not RTCP packets are subsequently
encrypted and/or integrity protected. The functioning of the AVPF
layer remains unchanged in SAVPF.
The AVPF profile derives from [1] the (optional) use of the
encryption prefix for RTCP. The encryption prefix MUST NOT be used
within the SAVPF profile (it is not used in SAVP, as it is only
applicable to the encryption method specified in [1]).
The SAVP part uses extra fields added to the end of RTP and RTCP
packets and executes cryptographic transforms on (some of) the
RTP/RTCP packet contents. This behavior remains unchanged in
SAVPF. The average RTCP packet size calculation done by the AVPF
layer for timing purposes MUST take into account the fields added
by the SAVP layer.
The SRTP part becomes only active whenever the RTP or RTCP was
scheduled by the "higher" AVPF layer or received from the transport
protocol, irrespective of its timing and contents.
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2.1 Packet Formats
AVPF defines extra packet formats to provide feedback information.
Those extra packet formats defined in [3] (and further ones defined
elsewhere for use with AVPF) MAY be used with SAVPF.
SAVP defines a modified packet format for SRTP and SRTCP packets
that essentially consists of the RTP/RTCP packet formats plus some
trailing protocol fields for security purposes. For SAVPF, all
RTCP packets MUST be encapsulated as defined in section 3.4 of [4].
2.2 Extensions
Extensions to AVPF RTCP feedback packets defined elsewhere MAY be
used with the SAVPF profile provided that those extensions are in
conformance with the extension rules of [3].
Additional transforms defined for SAVP following the rules of
section 6 of [4] MAY also be used with the SAVPF profile. The
overhead per RTCP packet depends on the transforms chosen. New
transforms added in the future MAY introduce yet unknown further
per-packet overhead.
2.3 Implications from combining AVPF and SAVP
The AVPF profile aims at -- statistically -- allowing receivers to
provide timely feedback to senders. The frequency at which
receivers are, on average, allowed to send feedback information
depends on the RTCP bandwidth, the group size, and the average size
of an RTCP packet. SRTCP adds extra fields (some of which are of
variable size) at the end of each RTCP packet that are probably at
least some 10 to 20 bytes in size (14 bytes as default). Note that
transforms defined in the future MAY add greater overhead. With
this, the average size of an RTCP packet will increase -- roughly
estimated by some e.g. 10% to 30% -- and thus reduce the frequency
at which (timely) feedback can be provided. Application designers
need to be aware of this, and take precautions so that the RTCP
bandwidth shares are maintained. This MUST be done by adjusting
the RTCP variable "avg_rtcp_size" to include the size of the fields
that will be added by SRTCP (index, E-bit, authentication tag, and
when present, the MKI). This means, for example, that the
definition of the avg_rtcp_size in Section 3.4 of [3] shall be
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calculated on the resulting SRTCP packet as described in Section
3.4 of [4].
3 SDP Definitions
3.1 Profile Definition
The AV profiles defined in [2], [3], and [4] are referred to as
"AVP", "AVPF", and "SAVP", respectively, in the context of e.g. the
Session Description Protocol (SDP) [3]. The combined profile
specified in this document is referred to as "SAVPF".
3.2 Attribute Definitions
SDP attributes for negotiating SAVP sessions are defined in [7] and
[8]. Those attributes MAY also be used with SAVPF. The rules
defined in [7] and [8] apply.
SDP attributes for negotiating AVPF sessions are defined in [3].
Those attributes MAY also be used with SAVPF. The rules defined in
[3] apply.
3.3 Profile Negotiation
Session descriptions for RTP sessions may be conveyed using
protocols dedicated for multimedia communications such as the SDP
offer/answer model [10] used with SIP, RTSP [11], or SAP [12] but
may also be distributed using email, NetNews, web pages, etc.
The offer/answer model allows the resulting session parameters to
be negotiated using the SDP attributes defined in [7] and [8]. In
the following subsection, the negotiation process is described in
terms of the offer/answer model. RTSP does not use the
offer/answer model; however specific negotiation support is
provided by [7] as discussed in subsection 3.3.2.
3.3.1 Offer/Answer-based Negotiation of Session Descriptions
Negotiations are carried out on a per-media session basis. If
negotiating one media session fails, others MAY still succeed.
Different RTP profiles MAY be used in different media sessions.
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For negotiation an media description, the four profiles AVP, AVPF,
SAVP, and SAVPF are mutually exclusive. Note, however, that SAVP
and SAVPF entities MAY be mixed in a single RTP session (see
section 4). Therefore, both MAY be offered as alternatives for the
same media session (e.g. using the same transport parameters).
An offerer that is capable of supporting multiple of these profiles
for a certain media session SHOULD always offer all alternatives
acceptable in a certain situation. At least, SAVP and SAVPF SHOULD
be offered as this does not impact security. However, the offers
SHOULD NOT include both a secure alternative (SAVP and SAVPF) and
an insecure alternative (e.g. AVP and AVPF) in the same offer as
this will most likely open up for bidding down attacks.
If a media description in an offer uses SAVPF and the answerer does
not support SAVPF, the media session MUST be rejected.
If a media description in an offer does not use SAVPF but the
answerer wants to use SAVPF, the answerer SHOULD reject the media
session. Alternatively, depending on whether or not offer is
otherwise acceptable, the answerer MAY accept the media description
and provide a counter-offer with a media description indicating
SAVPF in a subsequently initiated offer/answer exchange.
3.3.2 RTSP-based Negotiation of Session Descriptions
RTSP [11] does not support the offer/answer model. However, RTSP
supports negotiating media session parameters (including profile
and address information) by means of the "Transport:" header. SDP-
based key management as defined in [7] adds a parameter to support
conveying keying material.
Hence, the RTSP "Transport:" header MAY be used to pass keying
information and negotiate the profile for the media session. The
interoperability rules defined in section 3.3.1 SHALL apply.
3.3.3 Announcing Session Descriptions
Protocols that do not allow to negotiate session descriptions
interactively (e.g. SAP, descriptions posted on a web page or sent
by mail) pose the responsibility for adequate access to the media
sessions on the initiator of a session.
The initiator SHOULD provide alternative session descriptions for
multiple RTP profiles as far as acceptable to the application and
the purpose of the session. If security is desired, SAVP may be
offered as alternative to SAVPF -- but AVP or AVPF sessions SHOULD
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not be announced unless other security means not relying on SRTP
are employed.
The SDP attributes defined in [7] and [8] may also be used for the
security parameter distribution of announced session descriptions.
The security scheme description defined in [8] requires a secure
communications channel to prevent third parties from eavesdropping
on the keying parameters. Therefore, SAP encryption (as defined in
[12]), S/MIME [13], HTTPS [14], or other suitable mechanisms SHOULD
be used for distributing or accessing these session descriptions.
3.3.4 Describing Alternative Session Profiles
SAVP and SAVPF entities MAY be mixed in the same RTP session (see
also section 4) and so may AVP and AVPF entities. Other
combinations -- i.e. between secure and insecure profiles -- in the
same RTP session are not possible and SHALL NOT be used.
If both insecure and secure profiles shall be offered, different
RTP sessions MUST be used, expressed through different addresses
and/or port numbers. A grouping mechanisms as defined in [9]
SHOULD be used to indicate semantic equivalence between the
individual sessions and ensure that any receiver only joins one of
them.
[JO: Note that there is an open issue currently discussed in MMUSIC
regarding whether or not the same transport address may be used in
two or more m= lines and, if so, whether or not an explicit
grouping mechanism is required. The respective semantics also need
to be documented.]
For SAVP and SAVPF, the same RTP session MAY be used but it may be
advisable to also use different ones in order to allow optimal
support for feedback-enabled receivers.
In case the same RTP session shall be used for both SAVP and SAVPF,
two media sessions need to be defined in SDP. For the same RTP
session both will use the same address and port numbers. Those two
media sessions SHOULD be grouped by using the mechanism defined in
[9] to indicate semantic equivalence between the individual
sessions and ensure that any receiver only joins one of them.
3.4 Examples
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Example 1: The following session description indicates a secure
session made up from audio and DTMF [18] for point-to-point
communication in which the DTMF stream uses Generic ACKs. The key
management protocol is indicated in MIKEY. This session
description (the offer) could be contained in a SIP INVITE or 200
OK message to indicate that its sender is capable of and willing
to receive feedback for the DTMF stream it transmits. The
corresponding answer may be carried in a 200 OK or an ACK. The
parameters for the security protocol are negotiated as described by
the SDP extensions defined in [7].
v=0
o=alice 3203093520 3203093520 IN IP4 host.example.com
s=Media with feedback
t=0 0
c=IN IP4 host.example.com
m=audio 49170 RTP/SAVPF 0 96
a=rtpmap:0 PCMU/8000
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-16
a=rtcp-fb:96 ack
a=key-mgmt:mikey uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD...
Example 2: This example shows the same feedback parameters as
example 1 but uses the secure descriptions syntax [8]. Note that
the key part of the a=crypto attribute is not protected against
eavesdropping and thus the session description MUST be exchanged
over a secure communication channel.
v=0
o=alice 3203093520 3203093520 IN IP4 host.example.com
s=Media with feedback
t=0 0
c=IN IP4 host.example.com
m=audio 49170 RTP/SAVPF 0 96
a=rtpmap:0 PCMU/8000
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-16
a=rtcp-fb:96 ack
a=crypto:AES_CM_128_HMAC_SHA1_32
inline:d/16/14/NzB4d1BINUAvLEw6UzF3WSJ+PSdFcGdUJShpX1Zj/2^20/1
:32
Example 3: The following session description indicates a multicast
audio/video session (using PCMU for audio and either H.261 or
H.263+) with the video source accepting Generic NACKs for both
codecs and Reference Picture Selection for H.263. The parameters
for the security protocol are negotiated as described by the SDP
extensions defined in [7], used at the session level. Such a
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description may have been conveyed using the Session Announcement
Protocol (SAP).
v=0
o=alice 3203093520 3203093520 IN IP4 host.example.com
s=Multicast video with feedback
t=3203130148 3203137348
a=key-mgmt:mikey uiSDF9sdhs7494ghsd/dhsoKkdOokdo7eWsnDSJD...
m=audio 49170 RTP/SAVP 0
c=IN IP4 224.2.1.183
a=rtpmap:0 PCMU/8000
m=video 51372 RTP/SAVPF 98 99
c=IN IP4 224.2.1.184
a=rtpmap:98 H263-1998/90000
a=rtpmap:99 H261/90000
a=rtcp-fb:* nack
a=rtcp-fb:98 nack rpsi
Example 4: The following session description defines the same media
session as example 3 but allows for mixed mode operation of SAVP
and SAVPF RTP entities (see also next section). Note that both
media descriptions use the same addresses; however, two m= lines
are needed to convey information about both applicable RTP
profiles. The parameters for the security protocol are negotiated
as described by SDP extensions defined in [7], used at the session
level.
v=0
o=alice 3203093520 3203093520 IN IP4 host.example.com
s=Multicast video with feedback
t=3203130148 3203137348
a=key-mgmt:mikey uiSDF9sdhs7854ghsd/dhsoKkdOokdo7eWsnDSJD...
m=audio 49170 RTP/SAVP 0
c=IN IP4 224.2.1.183
a=rtpmap:0 PCMU/8000
m=video 51372 RTP/SAVP 98 99
c=IN IP4 224.2.1.184
a=rtpmap:98 H263-1998/90000
a=rtpmap:99 H261/90000
m=video 51372 RTP/SAVPF 98 99
c=IN IP4 224.2.1.184
a=rtpmap:98 H263-1998/90000
a=rtpmap:99 H261/90000
a=rtcp-fb:* nack
a=rtcp-fb:98 nack rpsi
Note that these two m= lines SHOULD be grouped by some appropriate
mechanism to indicate that both are alternatives actually conveying
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the same contents. A sample mechanism by which this can be
achieved is defined in [9].
4 Interworking of AVP, SAVP, AVPF, and SAVPF Entities
The SAVPF profile defined in this document is a combination of the
SAVP profile [4] and the AVPF profile [3](which in turn is an
extension of the RTP profile as defined in [2]).
SAVP and SAVPF use SRTP [4] to achieve security. AVP and AVPF use
plain RTP [1] and hence do not provide security (unless external
security mechanisms are applied as discussed in section 9.1 of
[1]). SRTP and RTP and not meant to interoperate, the respective
protocol entities are not supposed to be part of the same RTP
session. Hence, AVP and AVPF on one side and SAVP and SAVPF on the
other MUST NOT be mixed.
RTP entities using the SAVP and the SAVPF profiles MAY be mixed in
a single RTP session. The interworking considerations defined in
section 5 of [3] apply.
5 Security Considerations
The SAVPF profile inherits its security properties from the SAVP
profile; therefore it is subject to the security considerations
discussed in [4]. The SAVP profile does not add, nor take away,
any security services compared to SAVP.
There is a desire to support security for media streams and, at the
same time, for backward compatibility with non-SAVP(F) nodes.
Application designers should be aware that security SHOULD NOT be
traded for interoperability. If information is to be distributed
to closed groups (i.e. confidentially protected), it is RECOMMENDED
not to offer alternatives for a media session other than SAVP and
SAVPF as described in sections 3.3 and 3.4, unless other security
mechanisms will be used, e.g. the ones described in Section 9.1 of
[1]. Similarly, if integrity protection is considered important, it
is RECOMMENDED not to offer the alternatives other than SAVP and
SAVPF (unless other mechanisms are known to be in place that can
guarantee it, e.g. lower-layer mechanisms as described in Section 9
of [1]).
Offering secure and insecure profiles simultaneously may open to
bidding down attacks. Therefore, such a mix of profile offer SHOULD
NOT be made.
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AVPF makes packets larger than AVP. This has to be taken into
consideration with respect to the number of keystream bits that can
be generated for a given encryption transform in SRTP, to avoid
keystream re-use. For the pre-defined SRTP transforms, see [SRTP]
for maximum values.
Note that the rules for sharing master keys apply as described in
[7] (e.g., Section 9.1).
[Editors' note: The last paragraph needs expansion; parts of SRTP
should explicitly be spelled out here.]
Different media sessions may use a mix of different profiles,
particularly including a secure profile and an insecure profile.
However, mixing secure and insecure media sessions may reveal
information to third parties and thus the decision to do so MUST be
in line with a local security policy. For example, the local
policy MUST specify whether it is acceptable to have e.g. the audio
stream not secured and the related video secured.
The security considerations in [3] are valid too. Note in
particular, applying the SAVPF profile implies mandatory integrity
protection on RTCP. While this solves the problem of false packets
from members not belonging to the group, it does not solve the
issues related to a malicious member acting improperly.
6 IANA Considerations
The following contact information shall be used for all
registrations included here:
Contact: Joerg Ott
mailto:jo@acm.org
tel:+49-421-201-7028
The secure RTP feedback profile as a combination of Secure RTP and
the feedback profile needs to be registered for the Session
Description Protocol (specifically the type "proto"): "RTP/SAVPF".
SDP Protocol ("proto"):
Name: RTP/SAVPF
Long form: Secure RTP Profile with RTCP-based Feedback
Type of name: proto
Type of attribute: Media level only
Purpose: RFC XXXX
Reference: RFC XXXX
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All the SDP attribute defined for RTP/SAVP and RTP/AVPF are valid
for RTP/SAVPF, too.
NOTE TO THE RFC EDITOR: Please replace all occurrences of RFC XXXX by
the RFC number assigned to this document.
7 Acknowledgements
This document is a product of the Audio-Visual Transport (AVT)
Working Group of the IETF.
8 Authors' Addresses
Joerg Ott {sip,mailto}:jo@tzi.org
Uni Bremen TZI tel:+49-421-201-7028
MZH 5180
Bibliothekstr. 1
D-28359 Bremen
Germany
Elisabetta Carrara mailto:elisabetta.carrara@ericsson.com
Ericsson Research tel:+46-8-50877040
SE-16480 Stockholm
Sweden
9 Bibliography
9.1 Normative references
[1] H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson, "RTP
- A Transport Protocol for Real-time Applications," RFC 3550,
July 2003.
[2] H. Schulzrinne and S. Casner, "RTP Profile for Audio and Video
Conferences with Minimal Control," RFC 3551, March 2003.
[3] J. Ott, S. Wenger, N. Sato, C. Burmeister, J. Rey, "Extended
RTP Profile for RTCP-based Feedback (RTP/AVPF)," Internet
Draft draft-ietf-avt-rtcp-feedback-07.txt, Work in Progress,
June 2003.
[4] M. Baugher, D. McGrew, E. Carrara, M. Natslund, K. Norrman,
"The Secure Real-time Transport Protocol", Internet Draft
draft-ietf-avt-srtp-09.txt, Work in Progress, July 2003.
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[5] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels," RFC 2119, March 1997.
[6] M. Handley, V. Jacobson, and Colin Perkins, "SDP: Session
Description Protocol", Internet Draft draft-ietf-mmusic-sdp-
new-14.txt, September 2004.
[7] J. Arkko, E. Carrara, F. Lindholm, M. Naslund, and K. Norrman,
"Key Management Extensions for Session Description Protocol
(SDP) and Real Time Streaming Protocol (RTSP)," Internet Draft
draft-ietf-mmusic-kmgmt-ext-09.txt, Work in Progress, October
2003.
[8] F. Andreassen, M. Baugher, and D. Wing, "SDP Security
Descriptions for Media Streams," Internet Draft draft-ietf-
mmusic-sdescriptions-01.txt, Work in Progress, June 2003.
[9] G. Camarillo, J. Holler, G. Eriksson, H. Schulzrinne,
"Grouping of media lines in SDP," RFC 3388, December 2002.
[10] J. Rosenberg and H. Schulzrinne, "An offer/answer model with
SDP," RFC 3264, June 2002.
[11] H. Schulzrinne, A. Rao, and R. Lanphier, "Real Time Streaming
Protocol (RTSP)," RFC 2326, April 1998.
9.2 Informative References
[12] M. Handley, C. Perkins, and E. Whelan, "Session Announcement
Protocol," RFC 2974, October 2000.
[13] B. Ramsdell (ed.), " S/MIME Version 3 Message Specification,"
RFC 2633, June 1999.
[14] E.Rescorla, "HTTP Over TLS," RFC 2818, May 2000.
10 IPR Notice
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on
the IETF's procedures with respect to rights in standards-track and
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standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances
of licenses to be made available, or the result of an attempt made
to obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification
can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF
Executive Director.
11 Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
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it or assist in its implementation may be prepared, copied,
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However, this document itself may not be modified in any way, such
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must be followed, or as required to translate it into languages
other than English.
The limited permissions granted above are perpetual and will not be
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This document and the information contained herein is provided on
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ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
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THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
Ott, Carrara Expires March 2004 [Page 15]
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