ZyXEL Communications ISG50-ISDN Application Note page 44

Condition:
ISG50-1 (Main Office):
WAN IP: 59.124.163.156
Extension format: 4 digit
Prefix number before dialing to the remote office: 49
In outbound trunk setting, add a new trust peer in each ISG50 and set the remote WAN IP address as the trusted SIP server address.
ISG50-1 (Main Office):
ISG50-2 (Remote Office):
WAN IP: 59.124.163.147
Extension format: 4 digit
Prefix number before dialing to the main office: 48
ISG50-2 (Remote Office):
44