Telephone, device for communicating sound, particularly speech, commonly
by resources of wires in an electric circuit. The telephones now in common
use elaborated from the device fictional by Alexander Graham Bell and
patented by him in 1876 and 1877.
An apparatus including a transmitter used for transforming the acoustic signals
of a human's voice to electrical signals, a receiver for changing
electrical signals to acoustic signals and related signaling devices
for communicating with other humans using same apparatus
connected to a network. The term telephone also assigns to the elaborated
system of transmission paths and switching points connected to this
instrument. See also Telephone service.
Cellular telephone or cellular radio, telecommunications system in
which a mobile radio transmitter and receiver or telephone
is connected via microwave radio frequencies to base transmitter and
receiver stations that joint the user to a conventional telephone
network. The geographic region act by a cellular system is
subdivided into areas called cells. Each cell has a central base
station and two sets of allocated transmission frequencies; one set
is used by the base station and the other by mobile telephones. To
allow radio interference, each cell uses frequencies different from
those used by its surrounding cells, but cells adequate reserved
from each other can use the same frequencies. When a mobile telephone
leaves one cell and enters another, the telephone call is transferred
from one base station and set of transmission frequencies to the next
using a computerized switching system.

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