[asterisk-users] sip trunk, parsing DID

[Marc SCHAEFER]

Hello,

I am using a Swiss VoIP provider called sipcall. They have what they
call a SIP trunk, and it is less expensive than individual accounts. From
Asterisk's point of view, this is just a regular SIP account, which
can however receive and send calls from multiple numbers. I just migrated
from individual SIP accounts terminated on my Asterisk to one single
SIP trunk.

It works perfectly (in and out).  For outgoing calls, it's just
sufficient to set CALLERID(num) to the appropriate number you want the
call to originate from (easy!).

For incoming calls, here is an example SIP message, with MY_IP, SIPCALL_IP,
DEST_NUMBER AND SRC_NUMBER replacing the actual values:

   INVITE sip:s at MY_IP:5060 SIP/2.0
   Via: SIP/2.0/UDP SIPCALL_IP:5060;branch=z9hG4bK3ee1k92090iihapdm420.1
   Max-Forwards: 67
   Contact: <sip:SIPCALL_IP:5060;transport=udp>
   To: <sip:DEST_NUMBER at pro2.voipgateway.org>
   From: <sip:SRC_NUMBER at pro2.voipgateway.org>;tag=hy4fwr752woo42uj.o
   Call-ID: 1663976908-326811297 at 1~1o
   CSeq: 867 INVITE
   Expires: 300
   Allow: INVITE, ACK, BYE, CANCEL, INFO, SUBSCRIBE, NOTIFY, REFER, MESSAGE, OPTIONS, UPDATE
   Content-Disposition: session
   Content-Type: application/sdp
   User-Agent: PortaSIP
   h323-conf-id: 3912070954-288423879-3678105731-1479596074
   cisco-GUID: 3912070954-288423879-3678105731-1479596074
   Content-Length: 262

Since it looks that only the To: header contains the real destination number,
and debugging shows that it is not copied in ${CALLERID(all)} nor ${EXTEN}, I
had to revert to this hack, which works great:

   exten => s,1,Log(NOTICE, Incoming call from sipcall-trunk ${CALLERID(all)} to ${EXTEN} DID ${SIP_HEADER(To)})
   exten => s,n,Set(DID=${SIP_HEADER(To):})
   exten => s,n,Set(DID=${DID:5:11})
   exten => s,n,Log(NOTICE, Parsed DID: ${DID})
   exten => s,n,Goto(sipcall-trunk,sipcall-${DID},1)
   exten => s,n,Hangup()

I then have individual sipcall-NUMBER handling the actions for the individual
numbers.

Is there a simpler way?  Is there a safer way (check that DID only contains
numbers, e.g.?)

Thank you for any ideas or pointers.