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Call Processing
Issue 6 January 2008 127
Call Processing
Communication Manager gatekeepers
A gatekeeper is an H.323 entity on the network that provides address translation and controls
access to the network for H.323 endpoints. For Communication Manager platforms, these are
the Avaya S8300, S8400, S8500, and S8700-series Servers. H.323 RAS (Registration,
Admission, and Status) Protocol messages are exchanged between the server and the IP
endpoints for the endpoint registration.
All H.323 voice applications (IP Softphones, IP agents, and IP Telephones) should register with
an Avaya gatekeeper before any calls are attempted. Communication Manager sets up call
signaling (Q.931) and call control (H.245) channels from endpoints to the gatekeeper. This
allows Communication Manager to provide many of its calling features to H.323 calls.
Registration and alternate gatekeeper list
The RAS protocol is used by the IP endpoint to discover and register with the Communication
Manager gatekeeper.
When registration with the original gatekeeper (C-LAN, S8500 or S8300) IP address is
successful, the switch sends back the IP addresses of all the C-LANs (or LSPs) in the IP
Telephone’s network region. These addresses are used if the call signaling to the original
C-LAN circuit pack fails. Figure 47:
Discovery and registration process to the gatekeeper on
page 128 shows the registration process.