AT&T System 25 User Manual
Page 420
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.
E r l a n g
A traffic measuring unit that expresses the load of one or more
traffic-generating devices (36 CCS equals 1 erlang—see CCS
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
c a l l .
Facility (Physical)
A transmission channel to another switching system (a Central
Office, for example). By application, examples are:
●
CO Trunks
●
FX Trunks
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WATS Trunks
●
OCC Trunks
●
Tie Trunks
●
DS1 Tie Trunks.
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