ACS-160 Series & STL-160 Series T1 Mux Installation & Operation
6-Testing & Troubleshooting
Version 2.11, August 2011
6-4
Harris Corporation
Intraplex Products
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Equipment
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Line
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Payload
Generally, only one loopback is active at a time. However, the CM-5RB loopbacks are independent of
each other; you might want to have the line and equipment loopbacks active at the same time.
Warning!
Do not activate the payload and equipment loopbacks simultaneously. Doing so sets up a
feedback condition which sends the multiplexer into an alarm state.
6.3.1.1 Loopback Location and Function
If the LPBK indicator light on a CM-5RB module is on, one or more of its T1 loopbacks are active.
Figure 6-4 shows the location of the three loopbacks in relation to the channel modules and T1 circuit,
and Table 6-2 describes their functions.
Figure 6-4. T1 Loopbacks
Table 6-2. LPBK Group
Message
Function
Description
LnLB
Line
loopback
The entire T1 signal received by this module is looped (passed through to its T1 output).
Line code and frame format are passed from input to output without modification. Thus,
all line code (bipolar) violations, frame bit errors, and CRC-6 errors received by the CM-
5RB module are retransmitted without correction.
The line loopback forces the transmitted signal to be synchronized to the received signal.
However, the line loopback is located behind the CM-5RB jitter buffer so that any received
jitter is attenuated (Figure 6-3). Thus, while its line loopback is active, a CM-5RB module
is essentially loop timed. Once the line loopback is deactivated, the module returns to its
primary timing mode, which you set.
PaLB
Payload
loopback
The payload portion of the received T1 signal is looped (inserted into the payload portion
of the transmitted signal). However, the CM-5RB module itself generates the line code
and overhead bits (frame format) of the transmitted signal. Thus line code violations,
frame bit errors, and CRC-6 errors the CM-5RB module received are not passed through.
While the payload loopback is active, the CM-5RB module is automatically forced into the
loop timed mode. However, once the payload loopback is deactivated, the module returns
to its primary timing mode, which you set.
EqLB
Equipment
loopback
The payload portion of the transmitted T1 signal is looped into the payload portion of the
received T1 signal. Thus, you can use the equipment loopback to perform a local loopback
test on all of the payload circuits terminated by a CM-5RB module. While its equipment
loopback is active, a module transmits an unframed all ones signal, also known as the
alarm indication signal (AIS). Once the equipment loopback is deactivated, the module
returns to its primary timing mode, which you set.
6.3.1.2 Loopback State Review and Change
To review or change the loopback state on a CM-5RB module, perform these steps:
1.
Press up or down on the GROUP switch to display the LPBK group.
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