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Forward from ISDN to VoIP


How do I forward incoming calls from ISDN to VoIP?

We have a few numbers which are terminated on our ISDN 2 and 30 trunks and I'd like to forward them to a VoIP server.

We're running Cisco IOS Software, C3900 Software (C3900-UNIVERSALK9-M), Version 15.0(1)M4, RELEASE SOFTWARE (fc1) with CallManager Express.

If someone could take a look at the following dial-peer config and point out the issues, that would be great.

So, basically, all calls arriving onISDN for 123456789 should be forwarded to 123456789 but then over VoIP.

dial-peer voice 2001 pots
description From ISDN
incoming called-number 123456789
port 0/3/0:15

dial-peer voice 2002 voip
description To VoIP Server
destination-pattern 123456789
session protocol sipv2
session target ipv4:
session transport udp
voice-class sip dtmf-relay force rtp-nte
voice-class sip profiles 1
dtmf-relay rtp-nte
codec g711alaw
no vad

4 Replies 4

VIP Alumni
VIP Alumni

Hi Grant,

The 1st thing you need to do is to find out what signalling digits are actually being received from the CO on your ISDN link. I doubt very much that you will be receiving 9 digits, usually more like 6 or 4.

Try a q931 debug and make a call externally to the target number

Hopefully you should see an incoming call setup which will display the digits you are receiving

term mon
debug isdn q931

When finished no debug isdn q931

Once you know the digits you can then transpose to what ever destination number you need via
translation rules etc on your router or in you call server at the other end of the voip.


Regards, Alex. Please rate useful posts.