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Redirected call takes two "lines" from SIP trunk


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Just got a question from a customer that has a SIP trunk which is limited to 4 simultaneous calls.


One extension is redirected ("Call forward all calls to") an external number and they have many calls going that way.


The problem is that for each call that is redirected, two "lines" are taken until the call has ended. Is there any way we can configure it so that the SIP trunk provider sends signaling directly to the external number when calls are redirected?


Best regards,



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That discussion is as old as ISDN telephony. The answer is complex. One of the core questions is who pays for the redirected call. Other questions include how to achieve features like call recording, barge in, park, retrieve and so on. Once the call has left the PBX it is very difficult to get it back.


From a SIP point of view, the service provider must support 3xx redirection codes and REFER. AFAIK the number of providers that support it, is limited and the number of providers that support it properly, is very limited.


So the bottom line is: Make your life easy and get more lines. :unsure:

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No with snom ONE it is not possible. The only scenario where it would make sense would be call redirections after timeout or always; however even there the problem would be that if the redirection fails there is no way the PBX can handle the call any more. Cell phone forking would not work because features like twinning and PVA require that the PBX stays in the loop. Also, when the user presses ## the call will not get back to the PBX.

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