Because RFL™ and Hubbell® have a policy of continuous product improvement, we reserve the right to change designs and specifications without notice.
If the LPBK (loopback) indicator on a CM4 module is on, then one or more of its T1 loopbacks is
active. To review the state of the loopbacks on a given CM4 module, proceed as follows:
1. Press up or down on the GROUP switch to display the LPBK group.
2. Press down on the SET/NEXT switch one or more times to display the desired loopback
function. The green part of the ON/OFF indicator next to the FUNCTION display will light if
the displayed loopback is active; the red part will light if it is not active.
3. If you want to change the state of the displayed loopback, press up twice on the SET/NEXT
switch. The ON/OFF indicator will change state to indicate that the desired setup change has
taken place.
If you do not want to change the state of the displayed loopback, press down on
the SET/NEXT switch to display a different loopback, or press up or down on the
GROUP switch to leave the LPBK group altogether.
4.8 THE MEANING OF BLINKING INDICATORS (BLNK Group)
BLNK (Blink) group functions explain what is happening when the RX IN, RX OUT, or any of the
CM4 timing indicators are blinking (Table 4-4). BLNK functions will appear in the BLNK group only
when they are applicable; when no indicators are blinking, the BLNK group is empty. When one or
more indicators are blinking, one or more functions appear in the BLNK group to indicate why. For
example, if a T1 yellow alarm is detected by a CM4 receiver, the RX IN indicator on the CM4 module
will blink, and the function "RxY1" will appear in its BLNK group.
Table 4-4. BLNK group
Function Description
FTIM Fallback Timing. FTIM appears in the BLNK group when one of the timing indicators is blinking. It
means that the CM4 transmitter is in its fallback internal timing mode. This occurs when the CM4
module is configured to operate in the Looped, Through, or External timing
modes, but cannot do
so.
This is usually caused by one of the following:
1. A T1 facility failure.
2. A CM4 module failure.
3.
An
external timing source failure.
The INT indic
ator will light continuously when the CM
4 m
odule is in the fallback internal
timing mode.
RxYI Receive Yellow. When included in the BLNK group, the CM4 receiver detects a T1 Yellow Alarm
signal. A Yellow Alarm is produced by some types of T1 equipment, and indicates a loss of frame at the
far end. IMUX 2000 multiplexers do not
generate a Yellow Alarm upon loss of frame.
Rx11 Receive All Ones. When included in the BLNK group, the CM4 receiver detects a framed or unframed
all-ones signal. This indicates that the far end shelf is idle or set to Equipment Loopback.
XsJt Excessive Jitter. When included in the BLNK group, the CM4 T1 receiver jitter buffer has
overflowed. This normally indicates that the received T1 signal contains excessive timing j
itter.
M-DACS-T1 RFL Electronics Inc.
July 18, 2008 4-9 (973) 334-3100
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