[reSIProcate] Packet Fragmentation Issues, MTU and UDP

[Aron Rosenberg]

Our application is running into issues when we try and create an INVITE
with a large sdp that will go over 1500 total bytes. Our app prefers
UDP, but also has TCP added as transports. Our SIP domain has SRV
records which list udp before tcp for the sip domain.

 

We have several questions relating to MTU / large packet handling.

 

Is the resip stack supposed to handle fragmentation?

 

Does the resip stack check the interfaces MTU before it sends a packet
out? On Windows if we force a large INVITE it gets IP fragmented.

 

Should resip be setting the Don't Fragment bit in the IP header to
enable Path MTU discovery for UDP?

 

If a transaction is too large for the primary transport will resip
handle fallback to a second transport like TCP if SRV records are there?

 

Or is all of this the applications responsibility?

 

 

-Aron.

 

SightSpeed Inc.

http://www.sightspeed.com

 

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