Comdial DXP Plus Series, Руководство пользователя

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LIU Line Interface Unit
The line interface unit is the interface between the copper wires and the T1/PRI board’s framing circuitry. The
LIU is responsible for separating the 1.544MHZ receive clock from the incoming stream and converting bipolar
Alternate Mark Inversion (AMI) to 5–volt digital logic. The LIU also supports the automatic line build-out that
regulates the transmit level according to the receive strength (LIU-2 switch).
Primary Clock Reference
The straps on the DXSRV–PLS board designate the primary clock reference. Primary clock reference is the first
choice reference clock used to synchronize the DXP Plus to the incoming span. If the system looses
synchronization, it uses its secondary clock reference. If the secondary clock reference is not available, the
DXOPT-SYN card’s variable clock oscillator (VCO) switches to the fixed oscillator on the DXCPU (cpu) board.
When it does this, slips occur.
Repeater
A repeater is a amplifying device that central office technicians place at approximately one mile intervals along a
T1/PRI circuit to boost the T1/PRI signal. The T1/PRI specifications allow a maximum of 50 repeaters along a
communications path.
Slip
This term describes the condition that exists when the transmit 1.544 MHz clock is different from the receive
1.544 MHz clock. When the system collects or looses a frame of information due to the span frequencies being
different, the system generates a slip error. Slip does not affect voice transmissions and may not affect modem
traffic; however slip does effect digital data traffic. The T1/PRI board does not currently support digital data
traffic. Also, at times a central office takes a T1/PRI span out of service if too many slips occur—one or two a
day is permissible (the carrier supplier will furnish you with an an exact number if you request that information
from them).
IMI89–255 Installing And Programming The DXPRI Card
38 – Defining The T1/PRI Terms