draft-ietf-avt-rtp-framing-contrans-01.txt   draft-ietf-avt-rtp-framing-contrans-02.txt 
INTERNET-DRAFT John Lazzaro INTERNET-DRAFT John Lazzaro
March 27, 2004 CS Division June 24, 2004 CS Division
Expires: September 27, 2004 UC Berkeley Expires: December 24, 2004 UC Berkeley
Framing RTP and RTCP Packets over Connection-Oriented Transport Framing RTP and RTCP Packets over Connection-Oriented Transport
<draft-ietf-avt-rtp-framing-contrans-01.txt> <draft-ietf-avt-rtp-framing-contrans-02.txt>
Status of this Memo Status of this Memo
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Section 10 of RFC2026. or other IPR claims of which I am aware have been disclosed, and any of
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract Abstract
This memo defines a method for framing Real Time Protocol (RTP) and This memo defines a method for framing Real Time Protocol (RTP) and
Real Time Control Protocol (RTCP) packets onto connection-oriented Real Time Control Protocol (RTCP) packets onto connection-oriented
transport (such as TCP). The memo also defines how to specify the transport (such as TCP). The memo also defines how to specify the
framing method in a session description. framing method in a session description.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 2
2. The Framing Method . . . . . . . . . . . . . . . . . . . . . . . 2 2. The Framing Method . . . . . . . . . . . . . . . . . . . . . . . 2
3. Undefined Properties . . . . . . . . . . . . . . . . . . . . . . 3 3. Undefined Properties . . . . . . . . . . . . . . . . . . . . . . 3
4. Session Descriptions for RTP/AVP over TCP . . . . . . . . . . . . 4 4. Session Descriptions for RTP/AVP over TCP . . . . . . . . . . . . 4
5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Congestion Control . . . . . . . . . . . . . . . . . . . . . . . 6
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6 A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
B. Security Considerations . . . . . . . . . . . . . . . . . . . . . 6 B. Security Considerations . . . . . . . . . . . . . . . . . . . . . 6
C. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 6 C. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 7
D. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 D. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
D.1 Normative References . . . . . . . . . . . . . . . . . . . 7 D.1 Normative References . . . . . . . . . . . . . . . . . . . 7
E. Author Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 E. Authors' Address . . . . . . . . . . . . . . . . . . . . . . . . 8
F. Intellectual Property Rights Statement . . . . . . . . . . . . . 7 F. Intellectual Property Rights Statement . . . . . . . . . . . . . 8
G. Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 8 G. Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 8
H. Change Log for <draft-ietf-avt-rtp-framing-contrans-01.txt> . . . 9 H. Change Log for <draft-ietf-avt-rtp-framing-contrans-02.txt> . . . 10
1. Introduction 1. Introduction
The Audio/Video Profile (AVP, [1]) for the Real-Time Protocol (RTP, [2]) The Audio/Video Profile (AVP, [1]) for the Real-Time Protocol (RTP, [2])
does not define a method for framing RTP and Real Time Control Protocol does not define a method for framing RTP and Real Time Control Protocol
(RTCP) packets onto connection-oriented transport protocols (such as (RTCP) packets onto connection-oriented transport protocols (such as
TCP). However, earlier versions of RTP/AVP did define a framing method, TCP). However, earlier versions of RTP/AVP did define a framing method,
and this method is in use in several implementations. and this method is in use in several implementations.
In this memo, we document the method and show how a session description In this memo, we document the method and show how a session description
skipping to change at page 4, line 26 skipping to change at page 4, line 26
Section 2 does not define the RTP or RTCP semantics for closing Section 2 does not define the RTP or RTCP semantics for closing
a TCP socket, or of any other "out of band" signal for the a TCP socket, or of any other "out of band" signal for the
connection. connection.
Memos that normatively include the framing method MAY specify these Memos that normatively include the framing method MAY specify these
properties. For example, Section 4 of this memo specifies these properties. For example, Section 4 of this memo specifies these
properties for RTP sessions specified in session descriptions. properties for RTP sessions specified in session descriptions.
4. Session Descriptions for RTP/AVP over TCP 4. Session Descriptions for RTP/AVP over TCP
[3] defines how to specify connection-oriented media streams in session In this section, we show how session descriptions may specify RTP
descriptions. In this section, we show how to use [3] with the framing streams that use the framing method.
method.
Figure 2 shows the syntax of a media (m=) line [4] of a session Figure 2 shows the syntax of a media (m=) line [4] of a session
description: description:
"m=" media SP port ["/" integer] SP proto 1*(SP fmt) CRLF "m=" media SP port ["/" integer] SP proto 1*(SP fmt) CRLF
Figure 2 -- Syntax for an SDP media (m=) line (from [4]). Figure 2 -- Syntax for an SDP media (m=) line (from [4]).
[4] defines "TCP" as the <proto> token that specifies TCP transport. We To specify an RTP/AVP [1] [2] stream that uses the framing method over
now define how to declare that an RTP/AVP stream that uses the framing TCP, the <proto> token MUST be set to "TCP/RTP/AVP". To specify a
method appears on the TCP connection. Secure Real Time Protocol [6] stream that uses the framing method over
TCP, the <proto> token MUST be set to "TCP/RTP/SAVP".
At least two <fmt> tokens MUST follow <proto>. The first <fmt> token The <fmt> tokens that follow <proto> MUST be unique unsigned integers in
MUST be "RTP/AVP". Subsequent <fmt> tokens MUST be unique unsigned the range 0 to 127. The <fmt> tokens specify an RTP payload type
integers in the range 0 to 127, that specify an RTP payload type
associated with the stream. associated with the stream.
In all other respects, the session description syntax for the framing
method is identical to [3].
The TCP <port> on the media line exclusively receives RTP packets. If a The TCP <port> on the media line exclusively receives RTP packets. If a
media stream uses RTCP, a second connection exclusively receives the media stream uses RTCP, a second connection exclusively receives the
RTCP packets. The port for the RTCP connection is chosen using the RTCP packets. The port for the RTCP connection is chosen using the
algorithms defined in [4] and in related documents. algorithms defined in [4] and in related documents.
The TCP connections MAY carry bi-directional traffic, following the The TCP connections MAY carry bi-directional traffic, following the
semantics defined in [3]. Both directions of a connection MUST carry semantics defined in [3]. Both directions of a connection MUST carry
the same type of packets (RTP or RTCP). The packets MUST exclusively the same type of packets (RTP or RTCP). The packets MUST exclusively
code the RTP or RTCP streams specified on the media line(s) associated code the RTP or RTCP streams specified on the media line(s) associated
with the connection. with the connection.
The RTP stream MUST have an unbroken sequence number order. RTCP stream The RTP stream MUST have an unbroken sequence number order. RTCP stream
packets MUST appear as defined in [2], with no lost or re-ordered packets MUST appear as defined in [2], with no lost or re-ordered
skipping to change at page 5, line 29 skipping to change at page 5, line 31
5. Example 5. Example
The session descriptions in Figure 3-4 define a TCP RTP/AVT session. The session descriptions in Figure 3-4 define a TCP RTP/AVT session.
v=0 v=0
o=first 2520644554 2838152170 IN IP4 first.example.net o=first 2520644554 2838152170 IN IP4 first.example.net
s=Example s=Example
t=0 0 t=0 0
c=IN IP4 192.0.2.105 c=IN IP4 192.0.2.105
m=audio 9 TCP RTP/AVP 11 m=audio 9 TCP/RTP/AVP 11
a=direction:active a=setup:active
a=connid:1
Figure 3 -- TCP session description for first participant. Figure 3 -- TCP session description for first participant.
v=0 v=0
o=second 2520644554 2838152170 IN IP4 second.example.net o=second 2520644554 2838152170 IN IP4 second.example.net
s=Example s=Example
t=0 0 t=0 0
c=IN IP4 192.0.2.94 c=IN IP4 192.0.2.94
m=audio 16112 TCP RTP/AVP 10 11 m=audio 16112 TCP/RTP/AVP 10 11
a=direction:passive a=setup:passive
a=connid:1
Figure 4 -- TCP session description for second participant. Figure 4 -- TCP session description for second participant.
The session descriptions define two parties that participate in a The session descriptions define two parties that participate in a
connection-oriented RTP/AVP session. The first party (Figure 3) is connection-oriented RTP/AVP session. The first party (Figure 3) is
capable of receiving stereo L16 streams (static payload type 11). The capable of receiving stereo L16 streams (static payload type 11). The
second party (Figure 4) is capable of receiving mono (static payload second party (Figure 4) is capable of receiving mono (static payload
type 10) or stereo L16 streams. type 10) or stereo L16 streams.
The direction attribute in Figure 3 specifies that the first party is The "setup" attribute in Figure 3 specifies that the first party is
"active" and initiates connections, and the direction attribute in "active" and initiates connections, and the "setup" attribute in Figure
Figure 4 specifies that the second party is "passive" and accepts 4 specifies that the second party is "passive" and accepts connections
connections [3]. [3].
The first party connects to the network address (192.0.2.94) and port The first party connects to the network address (192.0.2.94) and port
(16112) of the second party. Once the connection is established, it is (16112) of the second party. Once the connection is established, it is
used bi-directionally: the first party sends framed RTP packets to the used bi-directionally: the first party sends framed RTP packets to the
second party on one direction of the connection, and the second party second party on one direction of the connection, and the second party
sends framed RTP packets to the first party in the other direction of sends framed RTP packets to the first party in the other direction of
the connection. the connection.
The first party also initiates an RTCP TCP connection to port 16113 The first party also initiates an RTCP TCP connection to port 16113
(16112 + 1, as defined in [4]) of the second party. Once the connection (16112 + 1, as defined in [4]) of the second party. Once the connection
is established, the first party sends framed RTCP packets to the second is established, the first party sends framed RTCP packets to the second
party on one direction of the connection, and the second party sends party on one direction of the connection, and the second party sends
framed RTCP packets to the first party in the other direction of the framed RTCP packets to the first party in the other direction of the
connection. connection.
6. Congestion Control
The RTP congestion control requirements are defined in [1]. As noted in
[1], all transport protocols used on the Internet need to address
congestion control in some way, and RTP is not an exception.
In addition, the congestion control requirements for the Audio/Video
Profile are defined in [2]. The basic congestion control requirement
defined in [2] is that RTP sessions should compete fairly with TCP flows
that share the network. As the framing method uses TCP, it competes
fairly with other TCP flows by definition.
A. Acknowledgements A. Acknowledgements
This memo, in part, documents discussions on the AVT mailing list about This memo, in part, documents discussions on the AVT mailing list about
TCP and RTP. Thanks to all of the participants in these discussions. TCP and RTP. Thanks to all of the participants in these discussions.
B. Security Considerations B. Security Considerations
Implementors should carefully read the Security Considerations sections
of the RTP [1] and RTP/AVP [2] documents, as most of the issues
discussed in these sections directly apply to RTP streams framed over
TCP. Implementors should also review the Secure Real-time Transport
Protocol (SRTP, [6]), an RTP profile that addresses the security issues
discussed in [1] [2].
Below, we discuss security issues that are unique to the framing method.
Attackers may send framed packets with large LENGTH values, to exploit Attackers may send framed packets with large LENGTH values, to exploit
security holes in applications. For example, a C implementation may security holes in applications. For example, a C implementation may
declare a 1500-byte array as a stack variable, and use LENGTH as the declare a 1500-byte array as a stack variable, and use LENGTH as the
bound on the loop that reads the framed packet into the array. This bound on the loop that reads the framed packet into the array. This
code would work fine for friendly applications that use Etherframe-sized code would work fine for friendly applications that use Etherframe-sized
RTP packets, but may be open to exploit by an attacker. RTP packets, but may be open to exploit by an attacker.
In addition to security issues related to RTP packet transport, there
are also security issues that concern the session descriptions of
connection-oriented media sessions. The security considerations section
of [3] describe these issues in detail.
C. IANA Considerations C. IANA Considerations
[4] defines the syntax of session description media lines. We reproduce [4] defines the syntax of session description media lines. We reproduce
this definition in Figure 2 of Section 4 of this memo. [4] defines this definition in Figure 2 of Section 4 of this memo. In Section 4, we
"TCP" as a token value for the <proto> field of media lines, and permits define two new token values for the <proto> field of media lines:
other memos to define tokens for the <fmt> fields that follow "TCP" on a "TCP/RTP/AVP" and "TCP/RTP/SAVP". Section 4 specifies the semantics
media line. associated with the <proto> field tokens, and Section 5 shows an example
of its use in a session description.
This memo defines <fmt> tokens for use with the "TCP" token. At least
two <fmt> tokens MUST follow <proto>. The first <fmt> token MUST be
"RTP/AVP". Subsequent <fmt> tokens MUST be unique unsigned integers in
the range 0-127. Section 4 of this memo specifies the semantics
associated with the <fmt> tokens.
D. References D. References
D.1 Normative References D.1 Normative References
[1] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson. [1] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson.
"RTP: A transport protocol for real-time applications", RFC 3550, July "RTP: A transport protocol for real-time applications", RFC 3550, July
2003. 2003.
[2] Schulzrinne, H., and S. Casner. "RTP Profile for Audio and Video [2] Schulzrinne, H., and S. Casner. "RTP Profile for Audio and Video
Conferences with Minimal Control", RFC 3551, July 2003. Conferences with Minimal Control", RFC 3551, July 2003.
[3] Yon, D. "Connection-Oriented Media Transport in SDP", work in [3] Yon, D. and G. Camarillo. Connection-Oriented Media Transport in
progress, draft-ietf-mmusic-sdp-comedia-05.txt. the Session Description Protocol (SDP),
draft-ietf-mmusic-sdp-comedia-07.txt.
[4] Handley, M., Jacobson, V., and C. Perkins. "SDP: Session [4] Handley, M., Jacobson, V., and C. Perkins. "SDP: Session
Description Protocol", work in progress, Description Protocol", draft-ietf-mmusic-sdp-new-18.txt.
draft-ietf-mmusic-sdp-new-14.txt.
[5] Bradner, S. "Key words for use in RFCs to Indicate Requirement [5] Bradner, S. "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
E. Author Address [6] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman.
"The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004.
E. Authors' Address
John Lazzaro John Lazzaro
UC Berkeley UC Berkeley
CS Division CS Division
315 Soda Hall 315 Soda Hall
Berkeley CA 94720-1776 Berkeley CA 94720-1776
Email: lazzaro@cs.berkeley.edu Email: lazzaro@cs.berkeley.edu
F. Intellectual Property Rights Statement F. Intellectual Property Rights Statement
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procedures with respect to rights in standards-track and standards- procedures with respect to rights in RFC documents can be found in BCP
related documentation can be found in BCP-11. Copies of claims of 78 and BCP 79.
rights made available for publication and any assurances of licenses to
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The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
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G. Full Copyright Statement G. Full Copyright Statement
Copyright (C) The Internet Society (2002-2003). All Rights Reserved. Copyright (C) The Internet Society (2004). This document is subject to
the rights, licenses and restrictions contained in BCP 78, and except as
This document and translations of it may be copied and furnished to set forth therein, the authors retain all their rights.
others, and derivative works that comment on or otherwise explain it or
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The limited permissions granted above are perpetual and will not be
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Acknowledgement Acknowledgement
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
H. Change Log for <draft-ietf-avt-rtp-framing-contrans-01.txt> H. Change Log for <draft-ietf-avt-rtp-framing-contrans-02.txt>
[Note to RFC Editors: this Appendix, and its Table of Contents listing, [Note to RFC Editors: this Appendix, and its Table of Contents listing,
should be removed from the final version of the memo] should be removed from the final version of the memo]
In preparation for the upcoming draft-ietf-mmusic-sdp-comedia revision, Section 4-5 and Appendix C have been rewritten to conform to the changes
all mention of TLS has been removed from -01.txt. In addition, in draft-ietf-mmusic-sdp-comedia-07.txt. Added a Congestion Control
references have been updated. section, and rewrote Security Considerations.
The "Status of this Memo", "Intellectual Property Rights Statement", and
"Full Copyright" now use the RFC 3667/3668 conventions. The document
passes idnits, modulo bugs in the script.
The major unresolved issue concerns the inclusion of "TCP/RTP/SAVP" as a
<proto> token to support SRTP. We do this in Section 4. Does this
inclusion bring up the same sort of controversies that resulted in TLS's
removal from draft-ietf-mmusic-sdp-comedia-07.txt? If so, should we
face into those controversies, or should we remove "TCP/RTP/SAVP" from
this document? Comments welcome.
 End of changes. 

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