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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.
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 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].
2. Solution Overview
3. RTSP Extensions
4. Open Issues
5. IANA Considerations
6. Security Considerations
8.1. Normative References
8.2. Informative References
§ Authors' Addresses
§ Intellectual Property and Copyright Statements
Real-time Streaming Protocol (RTSP) [RFC2326] (Schulzrinne, H., Rao, A., and R. Lanphier, “Real Time Streaming Protocol (RTSP),” April 1998.)[I‑D.ietf‑mmusic‑rfc2326bis] (Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M., and M. Stiemerling, “Real Time Streaming Protocol 2.0 (RTSP),” March 2010.) 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] (Srisuresh, P. and K. Egevang, “Traditional IP Network Address Translator (Traditional NAT),” January 2001.). 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] (Schulzrinne, H., Rao, A., and R. Lanphier, “Real Time Streaming Protocol (RTSP),” April 1998.) has quite a long time suffered from the lack of a standardized NAT [RFC3022] (Srisuresh, P. and K. Egevang, “Traditional IP Network Address Translator (Traditional NAT),” January 2001.) 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] (Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M., and M. Stiemerling, “Real Time Streaming Protocol 2.0 (RTSP),” March 2010.). 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] (Westerlund, M. and T. Zeng, “The evaluation of different NAT traversal Techniques for media controlled by Real-time Streaming Protocol (RTSP),” January 2010.) 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.
This overview assumes that the reader has some familarity with how ICE [I‑D.ietf‑mmusic‑ice] (Rosenberg, J., “Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols,” October 2007.) works. As it primarily points out how the different ICE steps are accomplished in RTSP.
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.
To be written
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.
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an RFC.
To be written
|[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-19 (work in progress), October 2007 (TXT).|
|[I-D.ietf-mmusic-rfc2326bis]||Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M., and M. Stiemerling, “Real Time Streaming Protocol 2.0 (RTSP),” draft-ietf-mmusic-rfc2326bis-23 (work in progress), March 2010 (TXT).|
|[RFC2119]||Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML).|
|[RFC2326]||Schulzrinne, H., Rao, A., and R. Lanphier, “Real Time Streaming Protocol (RTSP),” RFC 2326, April 1998 (TXT).|
|[I-D.ietf-mmusic-rtsp-nat-evaluation]||Westerlund, M. and T. Zeng, “The evaluation of different NAT traversal Techniques for media controlled by Real-time Streaming Protocol (RTSP),” draft-ietf-mmusic-rtsp-nat-evaluation-02 (work in progress), January 2010 (TXT).|
|[RFC3022]||Srisuresh, P. and K. Egevang, “Traditional IP Network Address Translator (Traditional NAT),” RFC 3022, January 2001 (TXT).|
|Stockholm, SE-164 80|
|Phone:||+46 8 719 0000|
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