Because RFL™ and Hubbell® have a policy of continuous product improvement, we reserve the right to change designs and specifications without notice.
Situation:
The FRM (loss of frame) indicator on the terminal multiplexer at Location 1 comes on. Technicians at
Location 1 and Location 2 use successive loopbacks in an attempt to identify the fault as occurring in
one of the following:
1. The multiplexer at Location 1.
2. The E1 facility.
3. The multiplexer at Location 2.
Procedure:
1. Activate the Equipment Loopback (EqLB) in the multiplexer at Location 1. (It is assumed in
this example that the multiplexer at Location 1 is internally timed.)
If the FRM LED remains on, then this multiplexer has a fault.
If the FRM LED turns off, then this multiplexer is probably fine. Proceed to Step 2.
2. Deactivate the Equipment Loopback in the multiplexer at Location 1. The FRM indicator
should turn on again.
3. Activate the Line Loopback in the multiplexer at Location 2.
If the FRM indicator remains on at Location 1, then the E1 facility is probably the
source of the fault.
If the FRM indicator turns off, then the E1 facility is probably all right, leaving the
multiplexer at Location 2 as the likely source of the fault.
4. To further identify the cause of the fault in the multiplexer at Location 2, deactivate the Line
Loopback and activate the Payload Loopback in the Location 2 multiplexer.
If the FRM indicator remains on at Location 1, then the source of the fault is the
CM4 module in the Location 2 multiplexer.
If the FRM indicator turns off, then the fault may be related to the ones density of
the signal generated by the multiplexer at Location 2. This can mean either that
too many data channels are operating without bandwidth limitation (i.e. operating
at N x 64 Kbps rates instead of N x 56 Kbps rates), or that the system is set up to
use the AMI line code but should be set up for HDB3.
5. You can also perform these tests in the opposite direction, from Location 2 towards
Location 1, as shown in Figure 9-2.
IMUX 2000E1 RFL Electronics Inc.
January 23, 2004 9-4 (973) 334-3100
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