Cellular telephone systems use a unique kind
of switching. In a
major metropolitan area, a cellular service might involve 10 or 20 transceiver antennas,
all linked by land lines to a switching subsystem that may be centrally located or
distributed over the serving area according to traffic needs. The switching subsystem
connects each call to a central-office switch that is part of the standard telephone
network. The cellular system switch oversees cell site operations, sets up and disconnects
calls, and records call details for billing. The network of cell sites keeps track of the
location of the moving telephone being used in a call in progress, determining when the
call should be moved from one cell area to another while maintaining the proper
radio-transmission quality.