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12 RFC 5124
INTERNET-DRAFT Joerg Ott/Uni Bremen TZI
draft-ietf-avt-profile-savpf-01.txt Elisabetta Carrara/Ericsson
July 2004
Expires January 2005
Extended Secure RTP Profile for RTCP-based Feedback (RTP/SAVPF)
Status of this Memo
By submitting this Internet-Draft, each author certifies that any
applicable patent or other IPR claims of which the author is aware
have been disclosed, or will be disclosed, and any of which each
author becomes aware will be disclosed, in accordance with RFC 3668
(BCP 79).
By submitting this Internet-Draft, each author accepts the
provisions of Section 3 of RFC 3667 (BCP 78).
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Copyright (C) The Internet Society (2004). 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.6
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................................................8
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...................................13
9.2 Informative References.................................14
10 IPR Notice...................................................14
11 Disclaimer of Validity.......................................15
12 Full Copyright Statement.....................................15
13 Acknowledgment...............................................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.
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The RTP specification provides only rudimentary support for
encrypting RTP and RTCP packets. SRTP [4] defines an RTP profile
("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 needs 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
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several SDP session level descriptions to define (alternatives
of) the same RTP session for the same media type.
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.
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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.
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 extensions (e.g., 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 extensions
and transforms chosen. New extensions and transforms added in the
future MAY introduce yet unknown further per-packet overhead.
Finally, further extensions specifically to SAVPF MAY be defined
elsewhere.
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 (see Section 3.4 of [4]) adds extra
fields (some of which are of configurable length) 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 extensions and transforms
defined in the future, as well as the configuration of each field
length, MAY add greater overhead. With this, the average size of
an RTCP packet will increase 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
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variable "avg_rtcp_size" to include the size of the fields that are
added by SRTCP (index, E-bit, authentication tag, and when present,
the MKI, as well any other field introduced by possible new SRTP
extensions).
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 (e.g. of RTP profiles, codecs, transport addresses,
etc.) 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 of a 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 may 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 MUST reject the media session. The
answerer MAY 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 a key management protocol (including keying material).
Hence, the RTSP "Transport:" header MAY be used to negotiate the
profile for the media session. The interoperability rules defined
in section 3.3.1 SHALL apply.
When the mechanism in [7] is used, the key management protocol is
carried in the SDP description sent from the server to the client,
e.g. in the 200 OK in response to the client's DESCRIBE message.
3.3.3 Announcing Session Descriptions
Protocols that do not allow negotiate session descriptions
interactively (e.g. SAP [12], 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 and manipulation. Therefore, SAP security
(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.
Both insecure and secure profiles MAY be used in the same offer but
only for different RTP sessions (i.e. sessions with different
addresses and/or port number). A grouping mechanism 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.
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
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 indicated is 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
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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 should 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
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...
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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
the same contents. A sample mechanism by which this can be
achieved is defined in [9].
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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 are 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.
Note that the rules for sharing master keys apply as described in
[4] (e.g., Section 9.1). In particular, the same rules for avoiding
the two-time pad (keystream reuse) apply: a master key MUST NOT be
shared among different RTP sessions, and the SSRC MUST be unique
between all the RTP streams within the same RTP session that share
the same master key.
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The key management MUST be called to provide new master key(s)
(previously stored and used keys MUST NOT be used again), or the
session MUST be terminated, when 2^48 SRTP packets or 2^31 SRTCP
packets have been secured with the same key (whichever occurs
before).
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
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.
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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
(STD0064), July 2003.
[2] H. Schulzrinne and S. Casner, "RTP Profile for Audio and Video
Conferences with Minimal Control," RFC 3551 (STD0065), 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-09.txt, Work in Progress,
July 2004.
[4] M. Baugher, D. McGrew, M. Naslund, E. Carrara, K. Norrman,
"The Secure Real-time Transport Protocol", RFC 3711, March
2004.
[5] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels," RFC 2119, March 1997.
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[6] M. Handley, V. Jacobson, and Colin Perkins, "SDP: Session
Description Protocol", Internet Draft draft-ietf-mmusic-sdp-
new-18.txt, June 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-11.txt, Work in Progress, April
2004.
[8] F. Andreassen, M. Baugher, and D. Wing, "Session Description
Protocol Security Descriptions for Media Streams," Internet
Draft draft-ietf-mmusic-sdescriptions-06.txt, Work in
Progress, July 2004.
[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 Rights 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; nor does it represent that
it has made any independent effort to identify any such rights.
Information on the procedures with respect to rights in RFC
documents can be found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat 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
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Internet Draft draft-ietf-avt-profile-savpf-01.txt July 2004
of such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository
at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
11 Disclaimer of Validity
This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR
ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE.
12 Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is
subject to the rights, licenses and restrictions contained in BCP
78, and except as set forth therein, the authors retain all their
rights.
13 Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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