[asterisk-users] Following call forwards

[Benny Amorsen]

I have a challenge that is ending up quite interesting. I need to
identify which SIP phone "touched a call last", that is, which phone did
the last transfer or dialed the original call if no transfers were
done.

It is easy in the case of a regular, non-transfered call. Just put
something in callerid= in sip.conf, and that will show up in
${CALLERID}. The same with an attended transfer, since that is just
another outgoing call which gets bridged later.

Unattended transfers are not so difficult (at least not if the
asterisk version is reasonably new), because ${BLINDTRANSFER} is set,
and I can get the phone name from that.

It is much more difficult if call forwarding is set on the phone. Then
it just replies to requests with 302 Moved Temporarily. In that case
${BLINDTRANSFER} is not set. ${RDNIS} is set, but it is not always
easy or even possible to turn the dialed number into a phone ID.

Is there a variable I can check to see which phone did the redirect?


If you are asking yourself why I care, here is the (long) background
story:

In Sweden, there are local calls, national calls, and international
calls. National calls are prefixed with 0, international ones with 00.
Those are easy to handle.

Local calls start by [1-9], and I need to massage them into national
calls. There are several locations connected by IP, and they each
need to be able to dial local numbers, but the calls all exit at the
same location and the users would get all confused if their local
calls from Malmö end up connecting to a phone in Stockholm.

It's not so difficult in that specific case. Add context=frommalmoe to
sip.conf, and do something like this:

[frommalmoe]
exten => _Z.,1,Goto(outgoing,032${EXTEN},1)
exten => _0.,1,Goto(outgoing,${EXTEN},1)

(I have no idea what the real prefix for Malmö is, this is just an
example).

When you have phones all over the country it gets complicated though.
You need a context for each area code, and that gets unwieldy. It is
much easier to have a database of phones and their locations -- but
that does not work if someone sets their phone to forward calls to a
local number. I have no way to find out which area that number belongs
to. If I knew which phone did the transfer, I would know which area to
use.


/Benny

(I'm sure someone will now give me the solution in just one line)