Gatekeeper Functions
Gatekeepers are a component of an H.323 network—a network designed to
transport real-time traffic, such as voice, video, or collaborative data. A gatekeeper
interacts with endpoints, which are stations capable of placing H.323 calls, such as
a workstation running Microsoft NetMeeting or a Cisco CallManager.A gatekeeper
also interacts with gateways, which are devices capable of translating
H.323 traffic into other forms of traffic, and which were discussed in Chapter 3.
For example, gateways convert H.323 traffic into voice calls over the traditional
phone network or Integrated Services Digital Network (ISDN) calls, common
with videoconferencing.This chapter explores what a gatekeeper is and what
functionality it provides.
As defined by the H.323 protocol, the gatekeeper is required to perform a
certain set of functions.These required functions perform basic H.323 services.
For example, the gatekeeper locates endpoints that are receiving calls, relieving
endpoints of this task.The gatekeeper also controls overall participation in the
network as well as calls placed there. Additional functions are optional and may
add value in certain cases.The next two sections review both types of functions.
Gatekeepers use the H.225 protocol to communicate with endpoints and
gateways.The H.225 protocol has two basic parts: Registration, Admission, and
Status (RAS) and call signaling. Gatekeepers primarily use the RAS portion of
the H.225 protocol with endpoints and gateways for registration, admission, and
call control in the H.323 network. Endpoints and gateways also use the call signaling
portion of the protocol for call setup and tear down.