[Serusers] Max-Forwards missing in SER CANCEL during forking

Andres andres at telesip.net
Wed Jan 13 20:05:34 CET 2010


We encountered an issue in 0.9.6 when SER forks requests because there 
are several endpoints registered with the same account (ie office and 
home phones).  When one of the endpoints answers the call, SER sends a 
CANCEL to the other endpoints so they can stop further call processing.  
It turns our that this SER generated CANCEL does not contain the 
"Max-Forwards" header which apparently violates RFC3261.

Here is an example:
U SER IP:5060 ->
sip:3055551234 at;rinstance=C926AD943D258534F5F62913216C50ADC9D895D2;
  transport=udp SIP/2.0..Via: SIP/2.0/UDP;branch=z9hG4bK1c1e.32eeb702.1..
  From: "9545551234" <sip:9545551234 at>;tag=as7d1243c9..
  Call-ID: 4385c66230a310e714f020926aa2028c at
  To: <sip:3055551234 at X.X.X.X:5065>..CSeq: 102 CANCEL..
  User-Agent: Sip EXpress router(0.9.6 (i386/linux))..
  Content-Length: 0....     

Is there any fix or workaround for this?  How can we get that 
"Max-Forwards" header in the Message if it is internally generated by 
SER and no something that flows through the config script.


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