[Serusers] SER/Asterisk PSTN Call Transfer Issue.

Peter Gradwell peter at gradwell.com
Thu Sep 23 13:51:54 UTC 2004


We have a phone system consisting primarily of SER and Asterisk, and are
having trouble transferring inbound calls from the PSTN.

We believe the problem is basically that because our phones register
with SER, the Asterisk box never sees the call from the original callee
to the new callee.


caller --> PSTN --> Asterisk --> SER --> callee's SIP phone

callee's SIP phone --> SER --> new callee's SIP phone

when the original caller hangs up, the transfer is requested, however
Asterisk does not know anything about the second call shown above, and
so we see an error about "supervised transfer requested; callid not

We have found that if, in our SER config, we route 8<extension> through
Asterisk, having stripped off the leading '8', and on to the SIP phone
via SER, then it works, because Asterisk then 'knows' about the new
call, since the second call above becomes

callee's SIP phone --> SER --> Asterisk --> SER --> new callee's SIP phone

Of course, this is a rather inelegant fix, especially when we actually
have more than one PSTN gateway.  Does anyone know if there is a more
flexible fix, either on the SER or Asterisk side, that might fix our


peter gradwell. gradwell dot com Ltd. http://www.gradwell.com/
  -- engineering & hosting services for email, web and voip --
   -- http://www.peter.me.uk/  -- http://www.voip.org.uk/ --

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