Nortel Networks NN43001-314 - Manual (Page 51)

Survivability 51
If the main office Call Server fails and call processing services are provided
by an alternate Call Server, the MG 1000B IP Phones register with the
alternate Call Server and receive call processing services from it. If no
alternate Call Server is available, the MG 1000B IP Phones stay registered
with the main office TPS for ten minutes. At the end of the ten minutes, the
IP Phones reset and register with the call server. If a key on a particular IP
Phone is pressed before the end of the ten minutes, that telephone resets
and registers with the call server immediately after the key is pressed.
When the main office Signaling Server fails and an Alternate Signaling
Server is available, the MG 1000B IP Phones reset and reregisters with the
main office Call Server through 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 MG 1000B IP Phones reset and
register with the call server. IP Phones that were registered with the call
server before the main office Signaling Server failure was detected are
then redirected back to the main office and register with the Voice Gateway
Media Card. These telephones stay in Normal Mode. IP Phones that
registered with the call server after the main office Signaling Server failure
was detected stay registered at the Branch Office.
If the Main Office has VTRK applications on the failed Signalling Server, the
NCS de-registers the Main Office from its database. Therefore, redirection
from local mode cannot be completed. If the alternative Signalling Server
has no TPS services configured (for example, it is purely an NRS, Personal
Directory (PD) Server, or pure VTRK), once again, redirection cannot be
completed. The correct scenario occurs when the NCS has a static endpoint
for the Main Office Node IP so there is no VTRK dependency. All TPSs
configured at the Main Office have the same H.323 ID. The Branch Office
maintains a connection to the NCS, or alternative NCS. In this particular
case, IP Phones are redirected to the Main Office even when a primary
Signalling Server fails.
When an MG 1000B IP Phone powers up, it registers first with the MG
1000B TPS, and second with the MG 1000B Call Server. It is then
redirected to the main office by the call server. The MG 1000B TPS queries
the Primary NCS for the main office node IP address to redirect the IP
Phone. The NCS provides the IP based on BUID value. If there are several
routes for a particular BUID route, the smaller route cost factor is chosen.
If the Primary NCS is down or unreachable, the MG 1000B TPS queries
the Alternate NCS. If the MG 1000B TPS receives a positive response,
the MG 1000B IP Phone is redirected to the main office. If the Alternate
NCS is also down or unreachable,the MG 1000B TPS queries the Failsafe
NRS. If a successful response is received from the Failsafe NRS, the IP
Phone registers with the main office. Otherwise, if neither an Alternate
NRS nor a Failsafe NRS is available, the MG 1000B IP Phone remains in
Nortel Communication Server 1000
Branch Office Installation and Commissioning
NN43001-314 01.02 Standard
Release 5.0 20 June 2007
Copyright © 2007, Nortel Networks
.