IPIPGW SIP Adding prefixes

Unanswered Question
Mar 5th, 2008
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I have a Cisco IP-to-IP gateway using SIP only.

On one side of the IPIPGW I have several PBXs that have NAT'd addresses. On the other side is my ITSP.

I need each PBX to have their outbound calls prefixed with a unique number (eg 100#, 101#, etc) so that these can be billed per customer at the ITSP.

I have created seperate dial peers for each of the PBXs that appends the prefix but I cannot find any method of getting the PBXs to hit these dial peers. (It is not an option for the PBX to dial a unique prefix - this must be done in the IPIPGW).

I have tried creating unique "voice source-groups" per PBX with an access list that matches the PBXs IP and changes the carrier-ID. The carrier-ID then matches a dial peer.

This almost works OK - however the PBX is behind NAT and the ACL is matching the SIP URI, not the IP header. This is not acceptable as the PBXs may have overlapping private IP addresses.

Does anyone have a solution to this issue? I think what I am trying to achieve is quite straight forward (eg. PBX1 dials 012345678 and this is modified to 100#012345678, PBX2 dials 012345678 and this is modified to 101#012345678) but I cannot find a solution!

Any help would be much appreciated



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