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12 13 14 15 16 17 18 19 20 21 22 RFC 7825
Network Working Group M. Westerlund
Internet-Draft Ericsson
Intended status: Standards Track T. Zeng
Expires: January 8, 2008 July 7, 2007
An Network Address Translator (NAT) Traversal mechanism for media
controlled by Real-Time Streaming Protocol (RTSP)
draft-ietf-mmusic-rtsp-nat-05
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document defines a solution for Network Address Trans(NAT)
traversal for the media stream associated with an Real-time Streaming
Protocol version 2 (RTSP 2.0). The mechanism is based on Interactive
Connectivity Establishment (ICE) adapted for using RTSP as signalling
channel. The necessary RTSP protocol extensions and procedure is
defined in this document.
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Requirements Language
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 [RFC2119].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Solution Overview . . . . . . . . . . . . . . . . . . . . . . . 3
3. RTSP Extensions . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 8
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1. Introduction
Real-time Streaming Protocol (RTSP)
[RFC2326][I-D.ietf-mmusic-rfc2326bis] is protocol used to setup and
control one or more media streams delivering media to receivers. It
is RTSP's functionality of seting up media streams that get into
serious issues with Network Address Translators (NAT) [RFC3022].
Commonly the media will be totally blocked by the NAT unless extra
provisions are taken by the protocol. There is a clear and present
need for NAT traversal mechanism for the media setup using RTSP.
RTSP 1.0 [RFC2326] has quite a long time suffered from the lack of a
standardized NAT [RFC3022] traversal mechanism for the media.
However due to quality of the RTSP 1.0 specification, the work on
updating RTSP was forced to abandom RTSP 1.0 and instead defined RTSP
2.0 [I-D.ietf-mmusic-rfc2326bis]. RTSP 2.0 is similar to RTSP 1.0 in
many aspects but contain a number of significant differencies. It
also contain a well defined extension mechanism allowing for
extensions like NAT traversal to be defined in way that will be
backwards compatible with RTSP 2.0 peers not supporting the
extension. This extension isn't defined for RTSP 1.0 due to that it
can't be specified in any way such that it do not break RTSP 1.0
syntax, and thus create compatibility issues.
There has been a number of suggested ways of resolving the NAT-
traversal of media for RTSP. A large number are also used in
implementations. However as the evaluation of RTSP NAT traversal
solutions [I-D.ietf-mmusic-rtsp-nat-evaluation] for the media has
shown there are issues to consider. In the end a mechanism based on
Interactive Connectivity Establishment (ICE) was selected as it
allows also servers to be located behind NATs and also provide a good
mitigation against the security threat RTSP represent as Distributed
Denial of Service (DDoS) attack tool.
This document does not define a NAT traversal mechanism for the RTSP
signalling itself. That is for future work in the cases it is
needed. Which compared to the media is in fewer deployement cases.
In all cases the server i reachable on a public IP address the
traversal of NAT for the signalling will work. Issues only arise
when both server and client are behind NATs. Solution beyond static
configurations or proxy based solutions are for future studies.
2. Solution Overview
This overview assumes that the reader has some familarity with how
ICE [I-D.ietf-mmusic-ice] works. As it primarily points out how the
different ICE steps are accomplished in RTSP.
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1. The server includes in the session description an SDP attribute
to indicate that the server has ICE capabilites for this session.
This is an optimization that allows clients to not spend
resources in cases when the SDP indication is missing.
2. The client reviews the session description to determine what
media resources that are going to be setup. For each of these
media resources where the transport protocol supports
connectivity checks the client gathers candidate addresses. See
section 4.1.1 in [I-D.ietf-mmusic-ice]. The client also installs
the STUN servers on each of the local candidates.
3. A new RTSP Transport header parameter (name tbd) is used to
include all the candidates for each media resource in the SETUP
request the client sends. One of these candidates are promoted
to default candidate per transport stream required for the media
resource by including it as if ICE would not be used in the
dest_addr parameter.
4. The RTSP server receives the list of candidates for the media
resource to setup. It then gathers its candidates. For servers
having a public IP address a single candidate can be included and
promoted to default directly.
5. The server sets up the media and responds to the SETUP request if
otherwise succesfully with 200 OK respons. In that respons the
server includes its candidates in the server candidate parameter
and the default in the src_addr parameter. Servers not being
behind a NAT or other type of middlebox and with a single
candidate should not intitiate its connectivyt checks yet. If
behind a NAT or other middlebox should now initiate its
connectivity checks following the procedures described in Section
5.7 and 5.8 of [I-D.ietf-mmusic-ice].
6. The client receives the SETUP response and learns the candidate
address to use for the connectivity checks. Then it initiates
its connectivy checks. In other words it follows the procedures
in Section 6 of [I-D.ietf-mmusic-ice].
7. When a connectivity check from the client reahces the server it
should result in a triggered check from the server. This is why
severs not behind a middlebox can wait until this triggered check
to send out any checks for itself. This saves resources and
somewhat mittigates the DDoS potential.
8. When the client has concluded its connectivity checks and also
received connectiviy checks on the promoted candidates for all
the media components it can issue a PLAY request. If the
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connectivity checks have not concluded succesfully then the
client may send a new SETUP request assuming it has any new
information or thinks the server may be able to do more that can
result in succesful checks.
9. When the RTSP servers receives a PLAY request it checks if its
connectivity checks has concluded succesfully. If not it issues
a 1xx response to indicate that it is still working on the
connectivity checks. If the checks has failed it issues a 4xx to
indicate that unsuccessful completion of the checks to the
client. Upon sucess the server sends a 200 OK and starts
delivering media.
The client may release unused candidates by sending a new SETUP
request that only contains the used candidates. This SETUP request
shall only change the candidate list, and the default candidate to
the used ones. No other parameters should be changed. After
succesful completion of this request may the client release the
resources.
The client will continue to use STUN to send keep-alive for the used
bindings. This is important as normally RTSP play mode sessions will
only contain traffic from the server to the client. As many NATs
requires traffic from the client towards the server to keep the
bindings alive these keep-alives are vital.
3. RTSP Extensions
To be written
4. Open Issues
This whole draft is currently an open issues. The actual
implementation of ICE for RTSP is yet to be written down in all
necessary details.
5. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
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6. Security Considerations
To be written
7. Acknowledgements
8. References
8.1. Normative References
[I-D.ietf-mmusic-ice]
Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols",
draft-ietf-mmusic-ice-16 (work in progress), June 2007.
[I-D.ietf-mmusic-rfc2326bis]
Schulzrinne, H., "Real Time Streaming Protocol 2.0
(RTSP)", draft-ietf-mmusic-rfc2326bis-15 (work in
progress), June 2007.
[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.
8.2. Informative References
[I-D.ietf-mmusic-rtsp-nat-evaluation]
Westerlund, M., "The evaluation of different NAT traversal
Techniques for media controlled by Real-time Streaming
Protocol (RTSP)", draft-ietf-mmusic-rtsp-nat-evaluation-00
(work in progress), July 2007.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
January 2001.
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Authors' Addresses
Magnus Westerlund
Ericsson
Torshamsgatan 23
Stockholm, SE-164 80
Sweden
Phone: +46 8 719 0000
Fax:
Email: magnus.westerlund@ericsson.com
URI:
Thomas Zeng
Phone:
Fax:
Email: thomas.zeng@gmail.com
URI:
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