Nortel 1000 Fundamentals page 161

A CS 1000 with existing SIP trunks requires a configuration change to
be compatible with Office Communications Server. In order for a SIP
Trunk to communicate with Office Communications Server, the SIP
Transport Protocol must be configured as TCP, not UDP (see SIP Gateway
configuration). However, this is not valid when SPS in Proxy All mode is
used, since everything goes through SPS.
The default Local SIP Port of 5060 is required.
Figure 55
SIP Gateway configuration window
The Route Data Block (RDB) must have the prompts NCNA and NCRD configured
to Yes. Otherwise, calls that are "Twinned" to Office Communicator using PCA
do not work.
Nortel Converged Office Fundamentals — Microsoft Office Communications Server 2007
Copyright © 2005–2008, Nortel Networks
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Telephony Gateway and Services configuration 161
ATTENTION
Nortel Communication Server 1000
NN43001-121 01.03 Standard
Release 5.0 30 April 2008