[Freeswitch-users] Codec list truncation?

[Lawrence Conroy]

Part two:
 as an entirely separate thing (must remember not to hit return too fast), RFC3261 says (in section 18.1.1) that one must switch to TCP if within 200 bytes of the discovered path MTU (or 1300 bytes if the path MTU is unknown).
That's SIP actively trying to avoid fragments. However, the logic there is fairly old -- it kinda assumes that responses will never be more than 200 bytes larger than the original message, which is not the case for some IMS style stuff.

SO .. . the problem is with SIP's choices on when to use UDP and when to use TCP, not with the underlying transport or network.

all the best,
  Lawrence

On 21 Mar 2014, at 16:33, Ken Rice <krice at freeswitch.org> wrote:
> UDP doesn't handle fragmentation... This is why sip is required to use both
> UDP and TCP (if you exceed MTU you Must use TCP per the RFC)
> 
> There are things like compressed headers to help with this but that only
> goes so far when you have 1500+ bytes in the SDP alone...
> 
> 
> On 3/21/14 8:41 AM, "Pete Ashdown" <pashdown at xmission.com> wrote:
> 
>> On 03/21/2014 03:32 AM, Keith Laaks wrote:
>>> Hi,
>>> 
>>> Are you perhaps hitting the MTU limit?
>>> 
>> 
>> Are SIP transmissions limited to a single packet confined by MTU?  Why
>> not just continue the list in the next packet?
>> 
>> 
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> -- 
> Ken
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