[Freeswitch-users] SIP 500 overlappting requests

[Phil Quesinberry]

We're having intermittent problems receiving calls from a particular DID.
The basic scenario is as follows:
Carrier sends invite w/SDP
We respond w/OK and SDP when call is answered
Carrier sends another invite with incremented sequence number and updated
SDP (aren't they supposed to ACK/respond before doing this?)
We send SIP 500 - overlapping requests
Carrier sends BYE - terminating the call

Sometimes (rarely) the call completes, most of the time FS sends a 500 and
doesn't get the call.  This just started happening recently and does not
occur with any other DIDs, including other DIDs from the same carrier.  I
updated to the latest stable GIT to see if that might solve the problem but
I'm pretty sure this is on the carrier's end.  They're trying to blame it on
us since we're sending the 500 and suggested that we allow overlapping
requests.

I'm assuming that their end needs to acknowledge our answer OK/SDP before
sending their own but if that's the problem then it raises another question
in my mind: since the SIP transport is generally UDP, what if we don't
receive their ACK before receiving their subsequent invite/SDP?  This could
certainly happen and would cause the call to be rejected if the above is
true.

I updated to the latest stable GIT last night to rule that out as a possible
cause of the problem.  Is there a way to get FS to allow a limited number of
overlapping requests as a possible workaround?

If someone thinks this looks like it could be an FS bug, I'll file a Jira.

Here is a trace which shows this happening:
http://pastebin.freeswitch.org/22769

Thanks,

Phil Quesinberry
Q Systems Engineering, Inc.
Embedded Hardware/Software Development
 (410) 969-8002
http://www.qsystemsengineering.com <http://www.qsystemsengineering.com/> 

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