On the IPO:
1- Create a SIP Trunk
2 - ITSP is the IP of the other PBX
3 - No Authentication But Enter 1234567 as UN & PW (there is logic to this)
4 - Set the URI as "Use User Data" in all 3 cases
5 - Enter a unique Trunk Group Number for outgoing and imcoming calls, e.g. 55 In & Out
6 - Set your ICR to route SIP calls on this trunk to the relevent extension,e.g.:
ICR Digits 3XX
TG55
Destination 3N
ICR Digits 2XX
TG55
Destination 2N
(Making allowances for Extensions and Hunt Groups)
7- Outbound Short Codes
Make short codes to reach the extensions/Hunt Groups on the other PBX, e.g.
3XX
Dial 3N"@192.168.1.1"
TG55
2XX
Dial
2N"@10.0.0.1"
TG55
8 - SIP Tab of Each User on Both Sites:
SIP Name Extension Number
SIP Display Name (Alias) Extension Name
Contact Extension Name or Number
The call from Site A to Site B is as follows:
A dials 301. S/C Match 3XX so sends 301"@192.168.1.1" down TG55 as an invite message, TX.
The message header will show the caller id as "Name of Extension":<Contact Name or Number@IP Address>. Depending on the other PBX the alias or contact may be shown as caller id.