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September 1999 P/N 880-503284-001-A1 - page 61 / 65

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Diagnostics

With a loopback plug in the network port, any customer equipment connected to the NCC 2020 (or a data port of any DIU module assigned to the CSU) should see a loopback condition. If the customer equipment can report errors, it should indicate that no errors are being received.

A T1 loopback plug can be made by taking a male RJ-45 connector and placing two short jumper wires where a cable would normally go. One jumper is placed from pin one to pin five, the other jumper connects pin two to pin four. See Figure 5-5 for a drawing of a T1 loopback plug.

NOTE: When using a T1 loopback plug it may be necessary to temporarily change the timing selection in the CSU. If the CSU is set to recover network clock, it will be trying to recover a clock it is trying to recover, the clock frequency will drift. For this test, set the CSU clock source to Internal. Remember to change it back after the test.

Figure 5-5

T1 Loopback Plug

RJ -45 Connector

1

2

4

5

8

Cable Side

RJ-45 plug held with plastic latching tab unseen at bottom

Verilink NCC 2020 User Manual

5-13

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