If the SIP side of the network goes down and the extension are not able to communicate with the PBX, the below details how the FXS extensions can use the FXO port(s) to call out the legacy pstn and how pstn callers can reach FXS extensions.
Under Expert Config-> Dialplan, click ‘Modify’ for the “ To_SIP” dialplan.
The below dialplan configuration will take care of any FXS extensions that attempt to call through the PBX fail, and route out the FXO port(s)
The key point of the first row is to select ’99-Re-Presentation’ for the Group. When an FXS-> SIP call fails, it will be triggered with this call Group.
(details of call Group below)
When this happens, the Vega looks for the next dialplan rule that is part of this call Group and tries to route. This is where the 4th row is triggered. The previously failed FXS->SIP call that failed will now be sent to the SIP local loopback with whatever number was dialed.
Backing out of the ‘To_SIP’ dialplan and clicking ‘Modify’ on ‘To_FXO’ dialplan, we can see the next rule that is triggered, which is also part of the 99 – Re-Presentation call Group:
The previously call that was sent to sip local loopback is now triggered here on the first row of the To_FXO dialplan. The call that now comes from SIP will go out the first FXO port (0201)
The screenshot below simply shows you what SIP return codes,the 99- Re-Presentation call group triggers on.
So a call to SIP that is unreachable (due to SIP side down) is part of this Re-Presentation Group.