AT&T MERLIN LEGEND Release 3.1 System Manager's Manual page 364

About Telecommunications
Many of the terms and concepts involved in telephone communications have
been in use since Alexander Graham Bell made the first phone call in 1876.
Because understanding them will help you to understand how the system
works, this section contains a brief history and description of telephone
communications.
Basically, telephone communications involves four elements:
Telephone Station (Extension) Equipment. The telephone instrument
and/or other equipment (for example, a fax machine) used to transmit
and receive the telephone signal.
Transmission Facilities. The equipment and media (for example, wire,
cable, and optical fiber) that provide the communications path that
carries the telephone signal.
Switching Equipment. The equipment that makes the electrical cross
connections so that the caller is connected to the called party.
Signaling. The transmission of information that controls the network, for
example, alerting the switch that a user wants to make a call, transmitting
the telephone number of the called party, and alerting the called party of
the call. Signals also tell the switch about how to make the connections.
This appendix provides information about each of the elements.
B
System Manager's Guide
B–1