How to configure a SIP trunk between Cisco Call Manager 5.x or 6.x or7.x and OCS 2007 R1 or R2

If you want to ring from MOC to Cisco IP phone and back, then simple we will deal with it as if OCS is an IP PBX with its extensions 3xxx and you need to connect it with Cisco PBX with extensions 7xxx.

To do that we need a SIP trunk and for the SIP trunk to work fine we need to have some specific configuration on that trunk , remember any of these settings if they not configured right then you will not be able to make a stable calling between Cisco and OCS.

First we do the SIP trunk:

Now the SIP trunk which is acting like the bridge between the Cisco and the OCS is created, ok then we need now to create a criteria where this trunk is going to be used in. This is where is Pattern comes in where we will say if a Cisco phone set tries to dial extensions starting with 3xxx then you use the trunk which we have just created .

And from the way back from the OCS to Cisco, when the number is sent in the E164 format with the +, the Cisco will simply ignore all that and will take only the last 4 Digits which are the 7xxx.

Now you are ready to make the call and for the complete configurations from OCS side see this Guide.