RFL Electronics IMUX 2000 - ACTIVATING and DEACTIVATING CM4, T1 LOOPBACKS (LPBK Group)

Because RFL™ and Hubbell® have a policy of continuous product improvement, we reserve the right to change designs and specifications without notice.
4.7 ACTIVATING AND DEACTIVATING CM4, T1 LOOPBACKS (LPBK
Group)
The LPBK group activates or deactivates the three T1 loopback modes provided by the CM4 module:
equipment, line, and payload. (See Table 4-3.) In most cases, only one loopback will be active at a
time. However, the CM4 loopbacks are independent of each other, so it is possible for two loopbacks
(such as Line and Equipment) to be active at the same time. See Figure 4-3.
CAUTION
Do not activate the Payload and Equipment Loopbacks simultaneously. This sets
up a feedback condition that will send the multiplexer into an alarm state.
Table 4-3. LPBK group
Function Description
Line Loopback. When
active, the entire T1 signal received by the CM4 module is looped, or passed
through to its T1 output. Line code and frame format are passed from input to output without
modification. This means that all line code violatio
ns (bi
polar violations), frame bit errors, and CRC-6
errors received by the CM4 module are re-transm
itted without correction.
Line Lo
opback forces the re-transmitted signal to be sync
hronized to the
received signal. Since the Line
Loopback is located behind the CM4 Jitter Buffer, any received jitter is attenuated. (See Section 2
of this manual for more information.) A CM4 module is essentially loop-timed when its
LnLB
Line Loopback is active.
PaLB Payl
oad Loopback. When
active, the payload portion of the received T1 signal is looped, or inserted
into the payload portion of the transmitted signal. The transmitted signal's line code and overhead bits
(frame format) are generated by the CM4 module itself. This means that all line code violations,
frame bit errors, and CRC-6 errors received by the CM4 module are not passed through.
When
Payload Loopback is active, the CM4 module is automatically forced into the loop-timed mode.
Once the Payload Loopback is de-activated, the CM4 m
odule will return
to its primary timing mode
(the timing mode set by the user).
EqLB Equipment Lo
opback. When
active, the payload portion of the transmitted T1 signal is looped into the
payload portion of the received signal. Equipment Loopback may be use
d to perform a local loopback
test on all the payload circuits terminated by a CM4 module. When Equipment Loopback is active,
the CM4 module will transmit an unframed all-ones sign
al; this is called th
e Alarm Indication
Signal (AIS).
NOTE
Ten minutes after a Line Loopbnack, Payload Loopback or Equipment Loopback is initiated,
the loopback times out and resets to non-loopback mode.
M-DACS-T1 RFL Electronics Inc.
July 18, 2008 4-7 (973) 334-3100