Nortel Networks SRG50 - Manual (Page 37)

Chapter 4 CS 1000 considerations 37
SRG50 Configuration Guide
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, the IP Phone attempts to communicate with the SRG.
After communication with the SRG is established, the SRG redirects the IP Phone to the main
office. When the SRG IP Phone attempts to register with the main office, the SRG first queries the
Primary NRS for the main office Virtual Trunk node IP address to redirect the IP Phone. If the
Primary NRS is down or unreachable, the SRG queries the Alternate NRS, 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 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.
SIP/ H323 trunks are used for Voice traffic alone. Proprietary TPSAR protocol is used for WAN
link health check and for Main Office TPS address discovery through NRS.
However, they cannot call any SRG analog (500/2500-type) telephones or any external numbers
through the SRG trunks because the Virtual Trunks are not available. (SRG analog [500/
2500-type] telephones are accessible if alternate routing is available through the PSTN.)
For more information about virtual trunks for SRG50, see the Main Office Configuration for
Survivable Remote Gateway 50 (NN43001-307).
Recovery to normal mode
Once communication is re-established with the main office call server, all IP Phones at the branch
office that are in local mode automatically redirect and reregister to the main office and return to
normal mode operation. IP Phones that were busy at the time communication was reestablished
complete the call in local mode, and then reregister with the main office after the call is complete.
Testing the telephone in local mode
From normal mode, the branch user has the option of going to local mode manually using the Test
local mode feature. The test can be performed by the user at any time and does not require a
password. This test is invoked from any IP Phone at the branch office.
Nortel recommends testing local mode operation after changing the provisioning for a telephone
on the SRG.
To ensure that users do not forget to resume normal mode operation, the SRG redirects the
telephone to the main office to return the telephone to normal mode. This occurs if the telephone
remains registered to the SRG in test local mode for ten minutes (default setting). Alternatively,
the user can press the Quit key from the set to return to normal mode.