Cisco TelePresence Administrator's Manual page 80

Protocols
Field Description
Call time to The interval (in seconds) at
live which the VCS polls the
endpoints in a call to verify that
they are still in the call. Default
is 120.
Auto Determines whether it will
discover respond to
Discovery Requests
endpoints. The default is On.
Caller ID Specifies whether the prefix of
the ISDN gateway is inserted
into the caller's E.164 number
presented on the destination
endpoint.
Cisco VCS Administrator Guide (X8.1.1)
Usage tips
If the endpoint does not respond, the call will be disconnected.
The system polls endpoints in a call regardless of whether the
call type is traversal or non-traversal.
To prevent H.323 endpoints being able to register automatically
Gatekeeper with the VCS, set Auto discover to Off. This means that
sent out by endpoints can only register with the VCS if their Gatekeeper
Discovery setting is Manual and they have been configured with
the VCS's IP address.
Including the prefix allows the recipient to directly return the call.
Configuring H.323
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