In this scenario, an IP telephone and a nearby gateway that provides a connection to the PSTN are both registered to a primary server. The gateway is backed up by a Survivable Remote Server, and the IP telephone has some Survivable Remote Servers in its alternate gatekeeper list. The IP telephone dials 911, and then the LAN shuts down abnormally and recovers partially.

If both the IP telephone and the gateway can reregister to the primary server, no problem exists. Also, if both the IP telephone and the gateway are forced to register with the same Survivable Remote Server, no problem exists.

However, if the IP telephone or the gateway re-registers to a Survivable Remote Server and the other re-registers to the primary server, or if the IP telephone and the gateway re-register to different Survivable Remote Servers, a minor problem exists.

When the emergency response personnel call back, the server that the gateway is registered with determines that the IP telephone is unregistered. The server cannot forward the return call to the IP telephone. Instead, the server attempts to forward the call to a telephone that is equivalent to the sent ELIN.

Even with automatic Emergency Return Call Forwarding, select the Emergency Location Extension that is administered in the ip-network-map screen as follows: