I’ve been playing with Asterisk lately, and needed to get out to the PSTN. Since I had a Cisco AS5350 with a PRI attached for incoming RAS, I figured I could use that. I also had some DIDs on the line that I could use to separate voice and data calls.

Googling around, I couldn’t find a good example of anyone who has done it, so I was on my own.

My goals here were simple:

1. People dialing 555-1111 should be picked up by the AS5350’s internal modems
2. People dialing 555-222X should be forwarded to my Asterisk box for handling
3. The Asterisk box should be able to dial out using the PRI
   

Already the DIDs were assigned to this PRI, so that wasn’t a problem.

The configuration on the AS5350 is fairly straightforward once you get it working:

voice service voip

 sip

  ! Bind the SIP and RTP sessions to a known interface

  bind control source-interface FastEthernet0/0

  bind media source-interface FastEthernet0/0

! Normal T1-PRI configuration using all channels

controller T1 3/0

 framing esf

 linecode b8zs

 cablelength short 133

 pri-group timeslots 1-24

! Anything not picked up by a dial peer defaults to a modem call

interface Serial3/0:23

 isdn incoming-voice modem

! Use a data dial-peer to answer anything to 555-1111 with a modem

dial-peer data 10 pots

 incoming called-number 5551111

! Match inbound calls to the voice DIDs

dial-peer voice 100 pots

 incoming called-number 555222.

 ! All digits are collected and sent along

 direct-inward-dial

 forward-digits extra

! The IP leg of the call... send to the sip server defined below

dial-peer voice 200 voip

 destination-pattern 555222.

 session protocol sipv2

 session target sip-server

 ! Any digits collected after the call has been answers get forwarded

 dtmf-relay sip-notify rtp-nte

 ! I want g711 ulaw for a codec

 codec g711ulaw

! Anything else gets sent out the PSTN

! Note you need the data dial-peer above to accept modem calls, otherwise

! this dial-peer will give dialtone to anyone who calls!

dial-peer voice 1000 pots

 application session

 destination-pattern .T

 port 3/0:D

 forward-digits all

! define your SIP server

sip-ua

 authentication username USERNAME password PASSWORD

 ! xxx.xxx.xxx.xxx represents the Asterisk box

 registrar ipv4:xxx.xxx.xxx.xxx expires 3600

 sip-server ipv4:xxx.xxx.xxx.xxx

After that, it’s just a matter of configuring a sip peer in /etc/asterisk/sip.conf