Can Asterisk detect outgoing call forwarding?


We’re using Asterisk to make call outs. Is there a way for Asterisk to detect that the call gets forwarded from the receiving phone and the call is actually answered by another phone?

Thanks a lot!


Waiting online, can anyone answer? Really appreciate it.

Asterisk will only know if it is told that call forwarding has occurred, it can’t detect it otherwise. It’s unlikely you would be receiving such information.

On a SIP intranet, some devices, including suitably configured Asterisks will signal this. I don’t think you can expect it over the PSTN, even though the network may be able to signal it over digital lines.

Thank you jcolp for your response. Assuming Asterisk is signaled, how do I get hold of this signal, which Asterisk function can do it?

David If I understand you correctly, you’re saying if call is forwarded by Asterisk, Asterisk might be able to signal if configured properly. But a call forwarded by a landline phone or cell phone won’t be able to signal. Is that correct?

See for what is theoretically possible. Limitations of signalling protocols and channel drivers may further restrict this (e.g. analogue lines can’t signal it at all).

Similar capabilities probably exist in the PSTN, but they are probably not exposed, for privacy reasons. They are more likely to be exposed if the transferring party has an ISDN connection.

The only way you are likely to see this on teh PSTN is if you are connected via SS& which you are not.

As with voip and asterisk if you had sip this may be visible in the sip trace.

Why do you wan this? is it to get round Non Geo number mappings ?


Hi Ian,

Thank you for your reply. The reason we need this is for security considerations, we don’t want to deliver the message if the call gets transferred away from the number that is intended to receive the call. By SS& did you mean SS7? Do you know how to get connected to that?



Hi I meant SS7 (kept my finger on shift key) you will have to talk to your local PTO to see if they will supply you with cct, But it wont be cheap or simple.

You could speak to a PTO and ask the question about forwarding and if they can give an option.