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Cisco ATA 186 and Cisco ATA 188 Analog Telephone Adaptor Administrator’s Guide (H.323)
OL-4008-01
Chapter1 Cisco Analog Telephone Adaptor Overview
H.323 Overview
H.323 Gatekeepers
Gatekeepers are primarily responsible for pre-call and call-level control services for H.323 gateways.
Gatekeepers are an optional component in an H.323 system. However, if present, gatekeepers must
perform the following call setup and management services:
•Address translation for IP addresses originating from H.323 aliases (for example,
address_pool@cisco.com, for example) or E.164 addresses (for examp le, standard telephone
numbers)
•Admissions control for authorizing or rejecting access to H.323
•Bandwidth control for gateway bandwidth requirements
•Zone management for registered voice terminals, gateways and MCUs
When used in an H.323 system, gatekeepers can also (but are not required to) provide the following
functionality:
•Call control signaling using the gatekeeper Routed Call Signaling mo del
•Call authorization to restrict access to certain voice terminals or gateways, or to restrict access based
on time-of-day criteria
•Bandwidth management for the H.323 system that will enable the gateway to restrict access when
requested bandwidth is unavailable
•Call management including maintaining a list of active calls to indicate available and unavailable
voice terminals and gateways
H.323 MCUs
MCUs are endpoints in an H.323 network that support point-to-mu ltipoint conferences and consist of a
multipoint controller and at least one multipoint processor responsible for receiving voice, video, and
data streams. These streams are distributed to access points participating in a point-to-multipoint
conference.
H.323 Proxy Server
An H.323 proxy server is a proxy specifically designed for the H.323 pr otocol and examines packets
between two communicating applications. Proxies can determine the destination of a call and perform
call-connection steps, if necessary.
H.323 proxies perform the following key functions:
•Allow voice terminals that do not support Resource Reservation Protocol (RSVP) to connect to the
proxy through remote access or local area networks with relatively reliable quality of service (QoS).
Pairs of proxies can then be employed to develop tunnels across the IP network.
•Support routing of H.323 traffic that is separate from ordinary data traffic by using
application-specific routing (ASR).
•Enable H.323 to be deployed in networks that use private address space.
•Ensure network security by configuring the proxy server to allow only H.32 3 traffic over the
network.