5.3.2. Remote Digital Loopback (RDL)
The Remote Digital Loopback test checks the performance of both
the local and remote Model 1186s, and the communication link
between them. In this test, any characters sent from the originating
device to the remote unit will be returned (see Figure 12). Any data
sent from the remote DTE wil be ignored.
To perform a RDL test, follow these steps:
1. Activate RDL by moving front panel toggle switch DOWN to
"Remote". The TM LED on both local and remote units will light up.
2. Perform a BER (Bit Error Rate) test on the system, using BER tester
on the local end. BER test can also be performed using built-in
511/511E pattern generator. (See section 5.3.3 on how to use the built-
in 511/511E pattern generator.)
3. If the BER test equipment indicates a fault and the Local Analog
Loopback test was successful for both Model 1186s, there may be a
problem with the line between the units.
4. Upon completion of the RDL test, return the front panel switch to
the NORMAL position. The TM LED should turn off on both local and
remote units.
5.3.3. V.52 Test Pattern Generator
To use the V.52 BER test in conjunction with the Local or Remote
Loopbacks, follow these instructions:
1. Locate the "511/511E" toggle switch on the front panel of the Model
1186 and move it UP. This activates the V.52 BER test mode and
transmits a "511" test pattern into the loop. If any errors are present,
the local modem's red "ER" LED will blink intermittently.
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2. If the above test indicates no errors, move the V.52 toggle switch
DOWN, activating the "511/E" test with errors present. If the test is
working properly, the local modem's red "ER" LED will blink once every
two seconds. A successful "511/E" test will confirm that the link is in
place, and that the built-in "511" generator and detector are working
properly.
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Figure 12.
Remote Loopback Diagram
G.703/G.704
Network
Note: When the unit is set for Network Clock Mode, the unit will
derivew its timing from the G.703/G.704 Interface. Failure to connect
to G.703/G.704 may result in bit errors during the 511 or 511/E test.