Appendix A: Glossary
Some terms in this glossary were defined with the assistance of
Newton’s
Telecom Dictionary
, by Harry Newton. To order a copy, call 1-800-LIBRARY or
write to: Telecom Library Inc., 12 West 21 Street, New York, New York 10010.
2500 set
The standard single-line touch-tone desk telephone.
Busy Tone
A signal generated by the Central Office indicating that the line you are calling is busy.
Call Progress Tone
A tone sent from the switch to tell the caller of the progress of the call. Examples are audible
ringing, re-order, busy, timing, etc.
Central Office
Telephone company facility where subscribers’ lines are joined to switching equipment for
connecting other subscribers to each other, locally and long distance. (Also called CO.)
DTMF
Also called touch-tone. Dual-tone multi-frequency. Push-button telephone signaling.
Forced disconnect
Method used by the telephone company to clear a line. When the called party goes on-hook, the
Central Office returns an open (that is, drops loop current) of at least 800 ms to the calling party.
This is also known as Calling Party Control (CPC), or Cutoff On Disconnect (COD), or
Disconnect Supervision.
Ground start
One of two types of switched telephone lines (outside lines) typically leased from telephone
companies, the other type being loop start. A ground start telephone line initiates an outgoing
telephone line seizure by applying a local resistance up to 550 ohms from ground to the tip
conductor.
Key telephone system
A telephone system in which the telephones have multiple buttons that permit a user to select
outgoing or incoming Central Office phone lines directly.
LED or light
Light-emitting diode. A semiconductor diode that emits light when a current is passed through
it. Used for status and information displays on electronic devices.
Loop start
One of two types of switched telephone lines (outside lines) typically leased from telephone
companies, the other type being ground start. A loop start telephone line is seized by connecting
a low resistance between the tip and ring (both wires) of the telephone line. This occurs
whenever a telephone or modem goes off-hook. If you need to find out if a line is loop start, call
the telephone company.
Off-hook
The telephone is in an off-hook state when the handset is removed from the cradle. A modem or
other device is off-hook when it answers a call or when it seizes a line to initiate a call.
Public Switched Telephone Network (PSTN)
Usually refers to the worldwide voice telephone network accessible to all those with telephones
and access privileges (In the U.S., it was formerly called the Bell System network or the AT&T
long distance network.)
Reorder Tone
A tone that sounds like the busy signal, but is twice as fast. It indicates that all switching paths
are busy. If you hear a reorder or fast busy, hang up and dial the number again.
Reference Manual
Appendix A: Glossary
40-400-00033, Rev.
C
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