GLOSSARY
Dual-Tone Multifrequency (DTMF)
Industry terminology for touch-tone calling.
Emergency Transfer Unit (ETU)
Provides direct connection of designated Power Failure Transfer
(PFT) registered voice terminals to the CO during a power failure or
other service interruption.
Erlang
A traffic measuring unit that expresses the load of one or more
traffic-generating devices (36 CCS equals 1 erlang—see CCS
[Hundred Call Seconds]).
Extension Number
A 1- through 4-digit number assigned to each voice terminal and
data endpoint in the system. Also see “Personal Dial Code.”
External Call
A connection between a system user and a party on the public
telephone network or on a tie trunk. Also referred to as an outside
call.
Facility (Physical)
A transmission channel to another switching system (a Central
Office, for example). By application, examples are:
● CO Trunks
● FX Trunks
● WATS Trunks
● OCC Trunks
● Tie Trunks
● DS1 Tie Trunks.
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