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Voice over IP 611

The components are as follows:

Gatekeeper--The gatekeeper is the most important component. The gatekeeper controls
the H.323 zone and determines how calls may proceed and whether a zone can initiate or
receive calls. The gatekeeper converts E.164 destination addresses into IP destination
addresses to pass a VoIP packet to its next destination. Gatekeepers provide a means to
manage dial plans and call routing in a VoIP network. Without a gatekeeper, each VoIP
gateway would have to be directly mapped to every other destination. For large networks,
this could amount to thousands of dial-peer statements in each router, which would of
course be impractical. The gatekeeper allows for tandem switching. Gatekeepers provide
a central point for administration and resource allocation.

Gateways--Provide services that translate protocols and convert different information
formats, allowing connectivity with non-H.323 devices such as traditional telephone
networks. A Cisco router with a voice interface that is connected to the PSTN is an
example of an H.323 gateway. Gateways manage the call-signaling conversion and the
media-signaling conversion when connecting the dissimilar network.

Terminals--Provide real-time two-way multimedia communications. All endpoints must
support voice.

Multipoint control units--Provide conference bridging support for multiconferencing.

H.323 Protocol Stack

H.323 relies on several protocols to do its business. They are defined as follows:

IP Internet protocol--Routes packets through the Internet.

TCP protocol--Ensures that the packets are properly sequenced.

UDP connectionless protocol--Sends data from one device to another. Used by voice
packets.

H.225

H.225 provides the signaling needed to establish connectivity between an H.323 terminal and
an H.323 gatekeeper. In addition, H.225 provides location and discovery services and RAS
functionality, which includes registration, administration, and status information between the
two devices.

NOTE

As of version IOS 12.1.3, Cisco allows the router to also function as a gatekeeper. Check the
gatekeeper documentation for new software releases on CCO to verify the current state of
gatekeeper functionality.

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