Comdial DXP Plus Series, Руководство пользователя

Страница: 339 / 1176

Loopback Payload
The loopback payload feature is an ESF-only method of loopback which loops the network receive input
path to the remote T1 equipment’s transmit output path. This loopback method does not loop the first bit
of each frame to allow the DXPT1 board’s facility data link to continue to transmit maintenance
information. You can use switches SW2–7 and SW2–8 to manually initiate the payload loopback or you
can allow the network to send an FDL message to initiate or restore the payload loopback. The DXPT1
board goes out-of-service during the loopback time.
Loopback Remote
The loopback remote feature loops the network receive input path to the remote T1 equipment’s transmit
output path. The remote loopback feature terminates all traffic and halt any call processing. You can use
the SW2 switches to manually initiate remote loopback or you can allow the network to remotely initiate
the condition. In superframe mode with SW2–1 set to on, the network can send a special in-band pattern
(00010001000100010001.... min 5 seconds) to cause the DXPT1 board to automatically enter the remote
loopback mode. The network can disable the loopback by sending a different in-band pattern
(001001001001001001001.... min 5 seconds). In ESF mode, the DXPT1 board’s facility data link, or
maintenance channel, can enable and disable remote loopback automatically or you can set SW2–7 on
and SW2–8 off to manually enable remote loopback or set both switches off to manually disable the
feature. Loopback remote operation is applicable to superframd and extended superframe modes.
LIU Line Interface Unit
The line interface unit is the interface between the T1 copper wires and the DXPT1 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).
Loop Start T1 Trunk
Loop Start T1 Trunk is a network protocol that monitors outbound digits to the DXPT1 board. This
protocol does not support disconnect supervision. Loop start protocol supports the subscriber end of the
communications path but does not support the office (network) end.
Primary Clock Reference
The straps on the DXAUX 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 DXSRV
(services) 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 circuit to boost the T1 signal. The T1 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 DXPT1 board does not
currently support digital data traffic. Also, at times a central office takes a T1 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).
IMI89–207 Troubleshooting The DXPT1 Installation
4 – Troubleshooting The DXPT1 Installation