Overview Page 23 of 258
SRG supports the Geographic Redundancy feature. For further information about Geographic Redundancy, see Communication Server 1000: System Redundancy
In the event of a WAN failure, the SRG IP Phones lose communication with the main office. This causes the SRG IP Phones to reset and register with the SRG. The IP Phones then operate in Local Mode, providing services based on a limited SRG feature set, which has significant differences from the CS 1000 software. For further information about services and features supported on the SRG, refer to SRG50 Configuration Guide.
If the main office Call Server fails and call processing services are provided by an Alternate Call Server, the SRG IP Phones reset and reregister with the Alternate Call Server and receive call processing services from it. If no Alternate Call Server is available, the SRG IP Phones go to Local Mode while the SRG attempts to find an Alternate Call Server by way of the NCS.
If the main office Signaling Server fails and an Alternate Signaling Server is available, the SRG IP Phones reset and reregister with the SRG. The SRG will then query the NCS for the Alternate Signaling Server’s IP address. The SRG will redirect the IP Phone to the Alternate Signaling Server and continue to receive call processing services from the main office Call Server. If no Alternate Signaling Server is available, the SRG IP Phones reset and register with the SRG in Local Mode.
When an IP Phone at the SRG first boots up, it attempts to communicate with the SRG. After it establishes communications with the SRG, the SRG redirects it to the main office. When the SRG IP Phone attempts to register with the main office, the SRG first queries the Primary NRS (NCS) for the main office Virtual Trunk node IP address to redirect the IP Phone. If the Primary NRS (NCS) is down or unreachable, the SRG queries the Alternate NRS (H.323 Gatekeeper), if one is specified. If it receives a positive response, the SRG IP Phone is redirected to the specified main office. Otherwise, if neither a Primary or an Alternate NRS (H.323 Gatekeeper) is available, the SRG IP Phone remains in Local Mode, and receives call processing services from the SRG until communication can be reestablished.
SRG IP Phones in Normal Mode remain registered with the main office if the Primary NRS fails and no Alternate NRS is available. They can call any main office telephone or IP Phones in Normal Mode in other branch offices.
Main Office Configuration for Survivable Remote Gateway 50 Configuration Guide
