[Sip] Re: [Simple] UDP - what if response is bigger than 1500 bytes (ethernet MTU)?
Thomas Froment <Thomas.Froment@alcatel.fr> Wed, 19 July 2006 13:31 UTC
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Date: Wed, 19 Jul 2006 15:31:18 +0200
From: Thomas Froment <Thomas.Froment@alcatel.fr>
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To: Silvestr.Peknik@tietoenator.com, sip@ietf.org
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Cc: Milan.Kunc@tietoenator.com, simple@ietf.org
Subject: [Sip] Re: [Simple] UDP - what if response is bigger than 1500 bytes (ethernet MTU)?
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Silvestr.Peknik@tietoenator.com wrote: > Hello, > > Could someone help me with following problem? > > I am not sure what should be done when the response to SIP request sent > over UDP is bigger than 1500 bytes? It can happen e.g. when PUBBLISH > request is responded by 415 Unsupported Media Type and Accept, > Accept-Encoding and Accept-Language headers are added. > This is a good question: I think it was mentionned in last SIP WG IETF meeting that having responses greater than path MTU (-200 bytes) in SIP was not currently well specified. It was an open issue on draft-ietf-sip-hop-limit-diagnostics-03.txt which raises this problem since it leads naturally to send big SIP responses. SIP WG people may probably answer you if something is planned to handle this problem... Thomas > Thank you, > Silvestr Peknik > > Extract from RFC3261: > 18.1.1 Sending requests: > ... > If a request is within 200 bytes of the path MTU, or if it is larger > than 1300 bytes and the path MTU is unknown, the request MUST be sent > using an RFC 2914 [43] congestion controlled transport protocol, such > as TCP. If this causes a change in the transport protocol from the > one indicated in the top Via, the value in the top Via MUST be > changed. This prevents fragmentation of messages over UDP and > provides congestion control for larger messages. However, > implementations MUST be able to handle messages up to the maximum > datagram packet size. For UDP, this size is 65,535 bytes, including > IP and UDP headers. > > The 200 byte "buffer" between the message size and the MTU > accommodates the fact that the response in SIP can be larger than > the request. This happens due to the addition of Record-Route > header field values to the responses to INVITE, for example. With > the extra buffer, the response can be about 170 bytes larger than > the request, and still not be fragmented on IPv4 (about 30 bytes > is consumed by IP/UDP, assuming no IPSec). 1300 is chosen when > path MTU is not known, based on the assumption of a 1500 byte > Ethernet MTU. > ... > > _______________________________________________ > Simple mailing list > Simple@ietf.org > https://www1.ietf.org/mailman/listinfo/simple > > _______________________________________________ Sip mailing list https://www1.ietf.org/mailman/listinfo/sip This list is for NEW development of the core SIP Protocol Use sip-implementors@cs.columbia.edu for questions on current sip Use sipping@ietf.org for new developments on the application of sip
- [Sip] Re: [Simple] UDP - what if response is bigg… Thomas Froment
- [Sip] Re: [Simple] UDP - what if response is bigg… Vijay K. Gurbani
- [Sip] Re: [Simple] UDP - what if response is bigg… Aki Niemi
- [Sip] SIP Over UDP Samir Srivastava
- Re: [Sip] Re: [Simple] UDP - what if response is … Vijay K. Gurbani
- Re: [Sip] Re: [Simple] UDP - what if response is … Aki Niemi