3Com VCX V7000 Installation Manual page 117

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Post-Installation IP Messaging servers use the list of trusted endpoints on the Call
Steps Processing (Call) servers to determine whether to accept connections
from branch offices servers. After you install a branch office IP Telephony
and Messaging system, you must define the branch office server as a
trusted end point on the VCX Call Processing Server in the associated
regional office. If the Call Processing service in the branch office fails, the
IP Messaging software can still interact with the Call Processing Server in
the regional office.
For instructions on how to add trusted endpoints see the VCX
Maintenance Guide.