Nortel Networks Remote Gateway 50 - Manual (Page 23)

Overview Page 23 of 258
Main Office Configuration for Survivable Remote Gateway 50 Configuration Guide
SRG supports the Geographic Redundancy feature. For further information
about Geographic Redundancy, see Communication Server 1000: System
Redundancy (553-3001-307).
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.