Gatekeeper Overview
A attendant is an H.323 article on a arrangement that provides casework such as address
translation and arrangement acceptance ascendancy for H.323 terminals, gateways, and MCUs. The
primary functions of a attendant are acceptance control, area management, and E.164
address translation. Gatekeepers are logically afar from H.323 endpoints and
optional accessories in an H.323 arrangement environment.
These alternative gatekeepers can administer endpoints in an H.323 network. The endpoints
communicate with the attendant application the RAS protocol.
CHAPTER 8
Configuring H.323 Gatekeepers
Note The ITU-T specifies that although a attendant is an alternative accessory in H.323 networks,
if a arrangement does accommodate a gatekeeper, all H.323 endpoints should use it.
Gatekeepers accept binding and alternative responsibilities. The binding responsibilities
include the following:
■ Abode resolution: Calls basic aural an H.323 arrangement ability use an alias to
address the destination terminal. Calls basic alfresco the H.323 arrangement and
received by a aperture can use an E.164 blast cardinal to abode the destination
terminal. The attendant charge be able to boldness the alias or the E.164 telephone
number into the arrangement abode for the destination terminal. The destination endpoint
can be accomplished application the arrangement abode on the H.323 network. The translation
is done application a adaptation table that is adapted with allotment messages.
■ Acceptance control: The attendant can ascendancy the acceptance of the endpoints into
the H.323 network. It uses these RAS letters to accomplish this: Acceptance Request
(ARQ), Acceptance Confirmation (ACF), and Acceptance Adios (ARJ). Admissions
control ability additionally be a absent action that admits all requests.
■ Bandwidth control: The attendant manages endpoint bandwidth requirements.
When registering with a gatekeeper, an endpoint will specify its adopted codec.
During H.245 negotiation, a altered codec ability be required. These RAS messages
are acclimated to ascendancy this codec negotiation: Bandwidth Appeal (BRQ), Bandwidth
Confirmation (BCF), and Bandwidth Adios (BRJ).
■ Area management: A attendant is appropriate to accommodate abode translation, admission
control, and bandwidth ascendancy for terminals, gateways, and Multipoint Control
Units (MCUs) amid aural its area of control.
All of these gatekeeper-required roles are configurable. The afterward are optional
responsibilities a attendant can provide:
■ Alarm authorization: With this option, the attendant can bind acceptance to certain
endpoints or gateways based on policies, such as time of day.
■ Alarm management: With this option, the attendant maintains alive alarm information
and uses it to announce active endpoints or alter calls.
■ Bandwidth management: With this option, the attendant can adios admission
when the appropriate bandwidth is not available.
Figure 8-1 provides a sample cartography illustrating the alternation amid gatekeepers
and added H.323 arrangement components.
Endpoints attack to annals with a attendant on startup. When they appetite to communicate
with addition endpoint, they appeal acceptance to admit a alarm application a symbolic
alias for the destination endpoint, such as an E.164 abode or an e-mail address. If the
gatekeeper decides that the alarm can proceed, it allotment a destination IP abode to the
originating endpoint. This IP abode ability not be the absolute abode of the destination
endpoint, but it ability be an average address, such as the abode of a proxy or a
gatekeeper that routes alarm signaling. A Cisco attendant provides H.323 alarm management,
including acceptance control, bandwidth management, and acquisition casework for calls
in the network.
Figure 8-1 Alternation of Gatekeepers with H.323 Arrangement Components
Chapter 8: Configuring H.323 Gatekeepers 443
GK1 = Attendant 1
GK2 = Attendant 2
V
V
GK1 GK2
Phone1-1
1001
Phone1-2
1002
Phone3-1
3001
Phone3-2
3002
Phone2-1
2001
Phone2-2
2002
Gatekeeper
Gatekeeper can forward
calls to added gatekeepers.
Terminal
A Cisco Unified Communications Manager
cluster can be registered at the gatekeeper.
Gateways can be
registered at the gatekeeper.
Each endpoint can be
registered in one zone.
Gatekeeper
Gatekeeper can
control bandwidth and
admission control.
Endpoints can be
registered at the
gatekeeper.