User manual
ITU-T
International Telegraph and Telephone Consultative Committee. International body that develops
worldwide standards for telecommunications technologies.
Impedance
The combined effect of resistance, inductance and capacitance on a transmitted signal.
Impedance varies at different frequencies.
Jitter
The deviation of a transmission signal in time or phase. It can introduce errors and loss of
synchronization in high speed synchronous communications.
Loop Start
A two-way, two-wire (tip and ring) signaling method in which the current used for signaling
ows in a circuit (loop) between a telephone and PBX or a telephone and central ofce.
Seizure of the line is accomplished by going off-hook which causes current to ow in a circuit (loop).
Loop Current
The current that ows through the circuit from the telephone switch to the voice board when
the channel is off-hook
On-hook
The signaling state that occurs when a handset is sitting on the phone (the phone’s inactive state)
and the ash hook is depressed.
Off-hook
The signaling state that occurs when the handset is removed from the phone and the
ash hook is released. When a phone is taken off-hook it signals the central ofce or
PBX that it needs attention, for example, to make a call or to answering an incoming call.
Pay Tone
A tone advising users of a payphone that a payment is required.
PBX (Private Branch Exchange)
A private telephone exchange.
PCM (Pulse Code Modulation)
A procedure for adapting an analog signal (such as voice) into a 64 kbps digital bit stream
for transmission.
PRI
An application that uses a singal channel to carry the signaling for all other channels on a line.
On a T-1 line, the application uses channels 1 through 23 (B channels) to carry data, digital voice,
and compressed video. Channel 24 (D channel) carries the signaling for all 23 B channels.
On an E-1 line, the application uses channels 1 through 15 and 17 through 31 (B channels)
to carry data, digital voice, and compressed video. Channel 16 (D channel) carries the
signaling for all 30 B channels.
PSTN (Public Switched Telephone Network)
The telecommunications network commonly accessed by ordinary telephones, key systems,
PBX trunks and data equipment.
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User Manual
Public Switched Telephone Network (PSTN) Simulators