Nortel Meridian 1 Description, Installation And Operation page 30

Page 30 of 262 Description
553-3001-119 Standard 2.00 April 2000
The value of Time To Live that is specified for the Gatekeeper provides the
duration of the Registration.
Admission
Admission occurs when a client or Gateway attempts to make a call. The
Gatekeeper authenticates the Clients and Gateways involved. Admission
occurs between both the originating and terminating sides and the Gatekeeper
per H.323. The Gatekeeper maps between the originating and terminating
sides of the call (address translation). The mapping is a simple dynamic
mapping between the Gateway and client.
The Gatekeeper tracks the active calls for logging and debugging purposes.
Unregistration and disengage
The Gatekeeper also allows the opposing actions to registration and
admission, in the form of unregistration and disengage. These allow Clients
and Gateways to inform the Gatekeeper when they are finished using
services.
Registration renewal: Time To Live
As the Gatekeeper confirms the Client and Gateway registration in the initial
registration request, the Gatekeeper specifies a Time To Live message for the
Client and Gateway. This is a deadline by which the Clients and Gateways
must re-register in order to maintain registration. The purpose of Time To Live
is to allow Gatekeepers, Clients, and Gateways to know whether they are still
alive.
This is needed because an endpoint can become disconnected from the H.323
network without first unregistering with the Gatekeeper, or in case the
Gatekeeper goes out of service. The Gatekeeper unregisters an endpoint that
misses two consecutive registration renewals. If a call is ongoing when the
Gatekeeper unregisters an endpoint, the call may be dropped.
The Time To Live value ranges from 10 to 60 minutes (configurable through
the MAT IP Line application). The Clients and Gateways are required to
renew the registration with keepAlive indications within the specified time.