Cellular networks
A base station controls a group of transmitting/receiving
frequencies allocated by the network to that cell.
The base station has also the control over subscribers that
are currently in the cell area.
When a subscriber wants to make a call, the base station allocates
a transmitting frequency which is then used between the
subscriber and the base station.
When the subscriber moves into another cell, a handover takes
place, and a new base station takes over the control of the call
and assigns a new frequency that is different from the first. The
original frequency used in the first cell is released.