5.3 LOOP (V.54) DIAGNOSTICS
The Model 2715RC offers three V.54 loop diagnostics and is com-
patible with two Telco loop diagnostics. Use these diagnostics to test
the NTU and any communication links. These tests can be activated
via the switches on the fron panel or via signals on the serial port inter-
face.
5.3.1 Operating Local Loopback (LL)
The Local Loopback (LL) test checks the operation of the local
Model 2715RC, and is performed separately on each unit. Any data
sent to the local Model 2715RC in this test mode will be echoed
(returned) back to the user device (i.e., characters typed on the key-
board of a terminal will appear on the terminal screen).
To perform a LL test, follow these steps:
1.
Activate LL. This may be done in one of two ways:
a. Activate the “LL” signal on the DTE. If you are not sure
which lead is the “LL” signal, please refer to Appendix D.
b.
Move the toggle switch on the front panel to “Local”.
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 Model
2715RC.
5.3.2 Operating Remote Digital Loopback (RL)
The Remote Digital Loopback (RL) test checks the performance of
both the local and remote Model 2715RC, as well as the communica-
tion link between them. Any characters sent to the remote Model
2715RC in this test mode will be returned back to the originating device
(i.e, characters typed on the keyboard of the local terminal will appear
on the local terminal screen after having been passed to the remote
Model 2715RC and looped back).
LOS
The Loss of Sync LED lights when the unit loses
synchronization with the incoming signal. This
may happen when there is a framing mismatch
or a loss of signal. In unframed mode, the LOS
LED monitors the status of the transmit clock.
ALM
The alarm LED indicates the presence of a AIS
or RAI, or Out of Frame condition. The ALM LED
will blink on every half-second. Alarms may
occur due to:
•
Loss of Synchronization
• Loss of Frame
• AIS
• RAI
ERR
The error LED indicates various error conditions,
including framing bit errors, excessive zeros,
controlled slips, severe errors, or bit errors (when
sending V.52 test patterns). When sending a test
pattern, the LED will remain lit if the unit does
not receive the identical pattern. When it
receives the correct pattern, the LED will turn off.
If error insertion is on, the LED will blink once a
second if everything is operating properly.
TST
The test indicator LED blinks with a specific pat-
tern depending on the type of test mode. When
the unit is in local analog loop, the LED will blink
on briefly. When the unit is in remote loop, the
TST LED will blink off briefly. When the unit is
sending a test pattern or is putting the remote
unit into V.54 loopback, the TST LED will stay
on. These are the test modes:
• V.54 Loopback & V.52 Patterns
• D4 Line Loop (CO initiated)
• ESF Line Loop (CO Initiated)
• ESF Payload Loop (CO Initiated)
PWR
The power indicator LED will remain lit while the
unit is powered. It turns off when the unit is not
powered.
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