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QPC789 16-port Message Waiting Analog Line Card
553-3001-105
Standard 5.00
June 1999
Card interfaces
The 16-port message waiting analog line card passes voice and signaling data
over network loops. This interface is discussed in detail in “Peripheral
equipment” on page 6.
Subscriber line interface circuits
Each of the 16 lines on the card contains a hybrid subscriber line interface
circuit (SLIC) that terminates the loop tip and ring conductors with a balanced
600 ohm termination and provides a –48 V dc battery supply to the telephone.
This circuit provides supervision features (such as hook switch status),
longitudinal signal suppression, 2-wire to 4-wire single-ended conversion
and ring trip detection. Also included in this hybrid are analog filters, the
coder-decoder (codec) circuit, and the logic used to switch the message
waiting lamps.
The loop current is monitored by a hook-switch detector that informs the PBX
CPU of the status of the phone set. The two possible conditions are on-hook
(low loop current) or off-hook (high loop current). The 2-wire to 4-wire
conversion is accomplished using a differential amplifier that converts the
input differential signals (that are equal and opposite in amplitude) into a
transmit signal that is referenced to ground. The differential amplifier also
limits the transmission of any longitudinal signal that may by induced in the
2-wire loop. Echo cancellation is provided by adding the inverse of the
reflected signal to that of the transmitted signal.
A relay in each unit connects the TIP side of the 2-wire loop to a ringing
signal to apply ringing onto the line. The timing of the application of ringing
current is synchronized to the RSYNC signal to prevent switching during
current peaks. The ring-trip function is performed by an operational
amplifier. The ring-trip sensor senses the negative peak of the ringing voltage
and responds to the increase in this peak caused by the decrease in the line
impedance when the telephone goes off-hook. The ring-trip detector detects
off-hook conditions during both ringing and silence intervals.
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Страница 76: ...Page 52 of 290 Description 553 3001 105 Standard 5 00 June 1999 ...
Страница 98: ...Page 74 of 290 NT1R20 Off Premise Station Analog Line Card 553 3001 105 Standard 5 00 June 1999 ...
Страница 154: ...Page 130 of 290 NT5D11 Line side T1 Interface Card 553 3001 105 Standard 5 00 June 1999 ...
Страница 216: ...Page 192 of 290 NT5D33 and NTRB34 Line side E1 Interface Cards 553 3001 105 Standard 5 00 June 1999 ...
Страница 264: ...Page 240 of 290 QPC192 Off Premise Extension OPX Analog Line Card 553 3001 105 Standard 5 00 June 1999 ...
Страница 276: ...Page 252 of 290 QPC452 Basic 500 2500 Analog Line Card 553 3001 105 Standard 5 00 June 1999 ...
Страница 302: ...Page 278 of 290 QPC789 16 port Message Waiting Analog Line Card 553 3001 105 Standard 5 00 June 1999 ...
Страница 306: ...Page 282 of 290 List of terms 553 3001 105 Standard 5 00 June 1999 ...
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