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5.2 LOOP (V.54 & TELCO) DIAGNOSTICS
The NetLink-T1™ offers three V.54 loop diagnostics and is com-
patible with two Telco loop diagnostics. Use these diagnostics to test
the CSU/DSU and any communication links. These tests can be acti-
vated via the software control port (See Section 3.2.3 System
Diagnostics), via signals on the serial port interface or the front panel
switch.
5.2.1 Operating Local Loopback (LL)
The Local Loopback (LL) test checks the operation of the local
NetLink-T1™, and is performed separately on each unit. Any data sent
to the local NetLink-T1™ in this test mode will be echoed (returned)
back to the user device (i.e., characters typed on the keyboard of a ter-
minal will appear on the terminal screen).
T1/FT1 CSU/DSU
Model 2720/I
Ethernet
Device
Clock/
Data
Clock/
Data
To perform a LL test, follow these steps:
1.
Activate LL. This may be done in one of two ways:
a.
b.
2.
Verify that the data terminal equipment is operating properly
and can be used for a test.
3.
Perform a V.52 BER (bit error rate) test as described in
Section 5.3. If the BER test equipment indicates no faults,
but the data terminal indicates a fault, follow the manufactur-
er's checkout procedures for the data terminal. Also, check
the interface cable between the terminal and the NetLink-T1.
Internal
Clocking
Model 2720/X
Figure 8. Local Loopback
Enter Local Loop from the System Diagnostics/Statistics
menu and toggle the <Spacebar> until "LL" appears next
to the Local Loop option.
Toggle the front panel switch to the "Local" position.
T1/FT1 CSU/DSU
Model 2720/I
Receive
Recover
Clocking
Cable Span
Data
Model 2720/I
LLB Initiated
35
Ethernet
Device
Clock/
Data
Data
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