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The second phase of switching is call completion, which entails
the actual connection of the requesting outlet to the wanted
inlet utilizing the determined routing, and initiation of the
charging process. The third phase of switching is conversation.
The fourth and final phase is release, which is the disconnection
of the call, completion of the charge record, and restoration of
the network to the normal (idle) state.
In addition to switching activities, modern switching
equipment must also perform certain management functions (such as
automatically detecting and isolating system and component
malfunctions), as well as provide certain customer services (such
as call forwarding or coin return at a pay telephone when the
call is not completed).
The implementation of the various activities and functions
of the switching process is complicated by certain system
requirements, including availability, reliability, privacy, and
economy, which at times may conflict with one another. The first
requirement, availability, refers to the need to have sufficient
paths so that a connection can be made on demand. The
reliability requirement refers to the need to assure that the
system as a whole, or a particular connection, does not go down
(fail). The privacy requirement reflects the need to switch
correctly (to the desired customer exclusively) or not at all.
Intentional misconnections, such as those caused by attempts to
avoid proper charging, as well as accidental misconnections, must
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Last modified: May 25, 2011