[Users] SER PSTN Failover

[Darren Nay]

Hello All,

I am having a problem with the t_on_failure failure route using SER / 
OpenSER (I have tried them both)... I have been using SER for 2+ years 
now and am servicing 5000+ voip customers but now we are moving to a 
PSTN termination partner who does not have redundant gateways.  So I 
would like to setup SER so that I have call route advance to a 2nd PSTN 
carrier if the 1st fails.  However, I am running into some snags...

With my configuration the call is processed correctly if the 1st PSTN 
carrier takes the call.  However, when the failover happens then I get 
some odd behavior.   The call is initially setup correctly with the 
failover carrier, but then it hangs up after about 5-7 seconds and a new 
call comes in to the called number, and a loop begins where this same 
call keeps coming in one after another until SER is restarted.

I do get the following errors on the SER console.

 0(17304) forward_req: ERROR: cannot forward to af 2, proto 2 no 
corresponding listening socket
 0(17304) Warning: sl_send_reply: I won't send a reply for ACK!!
 0(17304) ERROR: sl_reply_error used: I'm terribly sorry, server error 
occurred (7/SL)

It almost seems as if the the 1st route PSTN carrier is not accepting my 
ACK when I send it in response to the 403 Forbidden that they send to 
me.  Then they just keep sending the 403 Forbidden over and over again.  
Each time that they do that then SER processes it as a failed call and 
starts a new call to the secondary PSTN carrier.  Does this sound 
possible?  Or am I way off base here? 

I have attached my basic lab test SER cfg that I have been using to test 
with.  Perhaps someone can tell me what I might be doing incorrectly?

Or - Is there a better way to do this?  ie. With AVP-Pops?  If so, does 
anyone have a sample configuration that I can look at?

Thanks so much for any help provided!!

Darren Nay
Ionosphere, Inc.
dnay at ionosphere.net
+1 864-678-3158


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