Telephone Line Emulator User’s Manual
40-400-00020, Rev. M
125
DSCWID
Spontaneous Call Waiting with ID and Disposition. Disposition is the ability of a screen
phone to perform certain actions regarding the waiting call, such as play a voice message,
send to voice mail, conference and others. Also known as Type 3 Caller ID.
Forced disconnect
Forced Disconnect is a 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.
FSK
Frequency Shift Keying - A modulation technique that defines bits 0 and 1 as different
frequencies for use in analog data transmissions.
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.
IRA
International Reference Alphabet.
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.
LE
Local Exchange, another name for Central Office, see C.O.
Line Seizure
Condition of the telephone line when loop current is being drawn by CPE
Line Reversal
see Polarity Reversal
Loop current
When a modem, telephone or fax card (etc.) seizes the line (i.e. completes the connection
between tip and ring terminals of the telephone cable) current flows from the positive
battery supply in the telephone central office, through the twisted pair in the loop, through
the card (or phone) and back to the central office negative terminal where it is detected,
showing that this telephone or telephone device is off hook. The fax card or modem can
detect problems such as disconnects, shutting down the connection or a busy signal.
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.
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