On Wed, 2009-02-25 at 08:55 +0000, Gabor Paller wrote:
> Hi,
> 
> I am curious about the best practices for transferring external incoming
> calls.
> 
> The scenario is very common: Source (an external number) calls target1
> (an internal number, SipX user). Target1 transfers the call to target2
> (another internal number). This models a common case of a secretary
> transferring calls.
> 
> I understand that SIP-wise, the scenario depends on REFER request sent
> from target1 device to the device representing the source. As the source
> is a PSTN number, the device representing the source is either a gateway
> or a SIP trunking equipment which don't know about the target2 internal
> number. What is the best way of getting the gateway/trunking equipment
> to know about target2?

The Refer-To url in the REFER request will be to
sip:n...@sipxecs-domain 
so the device that gets that REFER should send the INVITE for the new
call leg to the proxy for sipxecs-domain, which _will_ know what to do
with the NNNN extension number.

Interpreting the user-part (left of the '@') in a sip url is not
possible unless you are authoritative for the domain part (the right
side).  Many implementations attempt to do this, but it's wrong - no
matter what other attributes there are.


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