Dear Smith,
Depending on the setup and the configuration you can setup a SIP trunk between the two locations.
Let's assume the following, since you didn't provide any information :
1. You have the HQ with extensions starting with 1xx, PBX1 ip 1.1.1.1
2. You have a branch1 office with extensions starting with 2xx, PBX2 ip 2.2.2.2
3. You have a branch2 office with extensions starting with 3xx, PBX3 ip 3.3.3.3
For this you need to make in each location a SIP trunk that will communicate with the other locations.
PBX1 configuration:
create SIP2 trunk to PBX2
create SIP3 trunk to PBX3
create prefix 2 to route calls to SIP2 trunk
create prefix 3 to route calls to SIP3 trunk
have a prefix 1 for internall call routing
PBX2 configuration:
create SIP1 trunk to PBX1
create SIP3 trunk to PBX3
create prefix 1 to route calls to SIP1 trunk
create prefix 3 to route calls to SIP3 trunk
have a prefix 2 for internall call routing
PBX3 configuration:
create SIP1 trunk to PBX1
create SIP2 trunk to PBX2
create prefix 1 to route calls to SIP1 trunk
create prefix 2 to route calls to SIP2 trunk
have a prefix 3 for internall call routing
In case there are more branches the configuration will expand properly
PBXx
create SIP1 trunk to PBX1
create SIP2 trunk to PBX2
create SIP3 trunk to PBX3
create SIP4 trunk to PBX4
create SIPn trunk to PBXn
create prefix 1 to route calls to SIP1 trunk
create prefix 2 to route calls to SIP2 trunk
create prefix 3 to route calls to SIP3 trunk
create prefix 4 to route calls to SIP4 trunk
create prefix n to route calls to SIPn trunk
have a prefix x for internall call routing
The details on how to configure the above can be found in the
documentation.
Please let us know if the answer has been helpful or if you require further help.