Following the Call Flow
The Atlanta CallManager is configured to use the Atlanta Gatekeeper for call
admission control.Thus when a user in Atlanta dials 1466, the Atlanta
CallManager places a call request to the Atlanta gatekeeper.The CallManager
knows that g.711 CODECs are used, so it requests an 80 Kbps call to the Atlanta
gatekeeper.The Atlanta gatekeeper checks active calls and determines that if this
call is placed, the total bandwidth used will be less than the defined interzone
bandwidth of 1152 Kbps, thus the call is permitted.The Atlanta gatekeeper sees in
its zone prefix configuration that all four-digit calls beginning with 1 (1...) get
routed to the Boston zone.The Atlanta gatekeeper uses its zone remote configuration
to determine that the Boston zone is controlled by gatekeeper 10.64.1.2.The
Atlanta gatekeeper places a location request to 10.64.1.2 for destination 1466.
The Boston gatekeeper receives the request for location 1466. It uses its zone
prefix configuration to also determine the destination zone is Boston. Since this is
configured as a local zone, it attempts to find the endpoint or gateway for 1466,
but because no endpoints have registered with this number, it uses its defined
default technology prefix to route the call to any gateway that has registered a 7#
technology prefix.The Boston CallManager has registered with a 7# technology
prefix, so its IP address (10.64.1.3) is returned to the Atlanta gatekeeper, which
returns it to the Atlanta CallManager.
The Atlanta CallManager attempts to place the call to the Boston CallManager.
The Boston CallManager does not use a gatekeeper for call admission control.This
is because CallManager can only register with the gatekeeper for one zone.Yet the
Boston CallManager handles calls for three zones (Boston,Washington, and
Providence). Since the CallManager registers with only one zone it would have no
way to identify to a gatekeeper whether calls were actually being made from
Boston,Washington, or Providence.Thus the Boston CallManager uses Location
call admission control, which is configured directly on the CallManager.This
method allows the CallManager to track each IP phone by its geographical location
and monitor the number of calls (and thus bandwidth used) by each location.The
Boston CallManager has sufficient bandwidth and the call is completed.
Washington and Providence are placed in separate zones so that the
Boston gatekeeper can distinguish between them for other H.323 calls, such as
videoconferences.