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NT8D09 Analog Message Waiting Line Card
553-3001-105
Standard 5.00
June 1999
Functional description
Figure 61 shows a block diagram of the major functions contained on the
analog message waiting line card. Each of these functions are described in the
following sections.
Card interfaces
The analog message waiting line card passes voice and signaling data over
DS-30X loops and maintenance data over the card LAN link. These interfaces
are discussed in “Intelligent peripheral equipment” on page 18.
Line interface units
The analog message waiting line card contains 16 identical and independently
configurable line interface units (also referred to as circuits). Each unit
provides 600-ohm impedance matching and a balance network in a signal
transformer/analog hybrid circuit. Circuits are also provided in each unit to
apply the ringing voltage onto the line synchronized to the ringing current
zero crossing. Signal detection circuits monitor on-hook/off-hook status and
switchhook flash detection. Four codecs are provided to perform A/D and
D/A conversion of line analog voiceband signals to digital PCM signals. Each
codec supports four line interface units. The following features are common
to all units on the card:
— transmission and reception of scan and signaling device (SSD) signaling
messages over a DS30X signaling channel in A10 format
— loopback of SSD messages and pulse code modulation (PCM) signals for
diagnostic purposes
— correct initialization of all features, as configured in software, at
power-up
— direct reporting of digits dialed (500 telephones) by collecting dial pulses
— connection of –150 V dc at 1 Hz to activate message waiting lamps in
two telephone sets in parallel. The two sets must be the same type or the
neon series resistor in each set must be 54 K¾ or greater.
— lamp status detection (will not detect a failure of either lamp when
operating in parallel)
— disabling and enabling of selected units for maintenance
— 40 mA to sets with short circuit protection
Summary of Contents for NT1R20
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