[Kamailio-Users] switch to TCP when UDP message is bigger than MTU

Daniel-Constantin Mierla miconda at gmail.com
Mon Apr 20 18:36:13 CEST 2009



On 04/20/2009 06:03 PM, Sandro Bordacchini wrote:
> Hi all.
>
> I am doing some test about tcp/udp transport protocols in SIP and IP 
> fragmentation.
>
> I would like to test this behaviour, as stated in par. 18.1.1 of rfc3261:
>
>    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.
>
> To do this, I am running a OpenSer 1.3.2 with a "default" configuration 
> (and very simple: no accounting, no auth, no DB) and I have two SIP 
> phones registered on that server (for example, ext. 100 and ext. 101).
>
> When 100 calls 101, the INVITE reaches the OpenSer that appends some 
> "dummy" headers (I have added some append_hf in the route), just to let 
> the message be bigger than the MTU.
> The INVITE is routed towards 101 with UDP protocol and I have IP 
> fragmentation.
>
> Do you have some hint to get the OpenSer work as described in the RFC 
> (i.e. switch automatically to TCP)?
> Or is this only possible with UACs and not with proxies?
>   
old openser/kamailio does not do the transport conversion automatically. 
You can do it manually by forcing outgoing transport, but is hard to 
guess the size of the outgoing message from the config.

However, next release will have it -- sip-router.org core has this 
functionality already. See:
http://sip-router.org/wiki/core-cookbook/devel#udp_mtu
http://sip-router.org/wiki/core-cookbook/devel#udp_mtu_try_proto_proto

You can get the Sip-Router code (which includes not kamailio/openser 
modules but lacks some core functions and parameters) from GIT:
http://sip-router.org/wiki/git/sip-router-repository

That core cookbook is work in progress, you can see kamailio/openser 
version at:
http://www.kamailio.org/dokuwiki/doku.php/core-cookbook:devel

Cheers,
Daniel

-- 
Daniel-Constantin Mierla
http://www.asipto.com/





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