Nortel Networks NN43001-314

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 stayregistered

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

server before the main ofﬁce Signaling Server failure was detected are

then redirected back to the main ofﬁce and register with the VoiceGateway

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 Ser ver

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.323ID. The Branch Ofﬁce

maintains a connection to the NCS, or alternative NCS. In this particular

case, IP Phones are redirected to the Main Ofﬁce evenwhen a primary

Signalling Server fails.

When an MG 1000B IP Phone powers up, it registersﬁrst with the MG

1000B TPS, and second with the MG 1000B Call Server. It is then

redirected to the main ofﬁce by the callser ver. 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 areseveral

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 FailsafeNRS 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