TCP/IP Tutorial and Technical Overview - IBM Redbooks

Terminations
Terminations represent streams entering or leaving the gateway. Some
terminations, typically representing ports on the gateway, are automatically
created when the device activates. Other terminations are created when
required. These represent transient flows through the network, such as RTP
traffic flows and VoIP streams.
Contexts
Terminations are placed into contexts. This occurs when two or more termination
streams are connected together. A simple call might have two terminations per
context (one termination representing the end device and the other termination
representing the connection to the network). A conference call can have
numerous terminations per context, each termination representing one leg of the
conference.
Megaco uses a series of commands to manipulate terminations and contexts.
For example, the ADD command adds a termination to a context, and the
MOVE command moves a termination from one context to another. These
commands are sent from the call agent to the gateway.
20.5 ITU-T recommendation H.323
H.323 is an ITU-T standard originally developed for multimedia
videoconferencing over packet-switched networks and was later extended to
include IP telephony requirements. At the time of this writing, it is the most widely
deployed call processing protocol.
The initial version of H.323 was developed very rapidly. Work started on ITU-T in
May 1995 and was completed by June of 1996. Since that time, three additional
versions have been published.
20.5.1 H.323 architecture
There are four components in a standard H.323 network:
► Terminals
► Gateways
► Gatekeepers
► Multipoint control units
Chapter 20. Voice over Internet Protocol 739