Why do we need this application?
This sceanrio applies to companies hosting the IP PBX in the main office and branch offices running Ip phones off the remote IP PBX. The IP PBX is the main system element where all the SIP registrations and call setup of all IP phones and soft clients happen. Therefore all-time-connection of all the devices from the main office as well as from SOHO is important. However, due to the fact that system crashes and network failures happen, nobody can guarantee that the connection will remain on 100% of the time.

If the network connection with the main office is lost, the remote office would be isolated. The phones would not work, neither for calls within the office nor for emergency calls. This is unacceptable for most of the people.

This application will not only maintain a lifeline for receiving and placing calls in the remote office but also enable remote phones in the same office to communicate to each other when the PBX is unreachable.

How does it work?
All VoIP traffic is routed thru a special SIP device connected to the local network that has the smarts to monitor the connection with main IP PBX, and when it deems the main IP PBX unresponsive due to network failure it will take over the call control intercepting the SIP messages and re routing them. Of course it is required to have local landlines (not Voip) in the remote office connected to the smart device's FXO port(s). Calls between Ip phones in the same office would be routed within the LAN, emergency or any call to pstn would also be routed to the local landlines.
When the connection to the main IP PBX is restored the calls will start flowing thru it again as usual.

Implementation
As explained above, the smart SIP device is connected to the LAN and all IP phones configured to send all the traffic thru it. Two products fit the description for this smart device: one is the Intertex IX78 which is also a router and comes with one FXO port only, since all (voip and non-voip) traffic of the branch office flows thru it, the Intertex add the benefit of QOS and packet prioritization for VoIP calls; the other smart device is an Audiocodes Gateway configured for remote survivability that can handle 4, 8 or more local lines.
Please contact ABP tech to get the hardware and technical help needed.