[OpenSIPS-Users] b2b top-hiding ate a 491

Jeff Pyle jpyle at fidelityvoice.com
Thu Mar 17 21:11:22 CET 2011


The scenario is this:

       Adtran CPE
     Opensips proxy 1
     Opensips B2BUA
     Opensips proxy 2
       PSTN Gateway

Opensips is 1.6.4 installed from Debian packages in all cases.

The Adtran CPE placed a fax G729 call through the Opensips network and out
through the PSTN carrier.  After 200 OK, the PSTN carrier sent a re-INVITE
for G711.  At nearly the same time the Adtran CPE sent a re-INVITE for

The SIP traces at Opensips proxies 1 and 2 show each side sent a 491
Request Pending to the other.  The traces also show the Opensips B2BUA
running in top-hiding mode didn't pass the CPE->PSTN 491.  Consequently
the PSTN gw continued to reply with 491s to the CPE's repeated attempts to
go to T.38 since as far as it knew it still had an outstanding re-INVITE
of its own.

An examination of the Opensips B2BUA log has the following:

ERROR:b2b_entities:b2b_tm_cback: No dialog found reply 200 for method BYE,
[2566600-0-561c-4e442-737b62ad-4e442 at ww.xx.yy.zz]

This is probably because the call didn't tear down in the cleanest
possible way.  The two different proxies show slightly different versions
of the same thing, including 491s, and 501s for out-of-transaction BYEs.

Of course this is the perfect storm.  Being able to duplicate the timing
that caused the 491s in the first place is going to be next to impossible.
 My sipp knowledge is not up to the task I'm afraid.  My hope is perhaps
this is/was a known problem and it has already been corrected.  If not,
any thoughts on what might have caused the B2BUA to eat a 491?

- Jeff

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