5. If the BERT test indicates that errors are present, make sure that the Line Driver is plugged into the DTE properly. (IF the Line Driver is connected to a DTE across RS-232 cable, make sure the cable is pinned
straight through, is properly plugged in on both ends, and is not longer than 6 ft. If the Line Driver is connected to a DCE, make sure that the connecting cable is properly cross-pinned. Also, make sure the Line
Driver is configured properly. Then recheck your DTE equipment.
Remote Digital Loopback (RDL):
The Remote Digital Loopback (RDL) test checks the performance of both the local and remote Line Drivers, and the communication link between them. Any characters sent to the remote Line Driver in this test mode will be
echoed (returned) back to the originating device. For example, characters typed on the keyboard of the local terminal will appear on the local terminal's screen after having been passed to the remote Line Driver and looped
back. To perform an RDL test, follow these steps:
1. Activate RDL. You can do this in either of two ways. One is to move the right-hand front-panel slide switch labeled "LOOP" to the "RDL" (up) position. The other is to raise the signal on Pin 21 of the RS-232
interface switch SW2 position 8 must be "OFF". Once the RDL is activated, the remote Line Driver's receive input is connected to its own transmitter. The TEST LED should light on both Line Drivers.
2. Verify that the DTE attached to the local Line Driver is operating properly and can be used for a test.
3. Move the left-hand top-panel slide switch labeled "BERT" to the "511" (down) position. This will activate the V.52 BERT test mode and inject a 511 test pattern into the local loop. If any errors are present in the loop,
the Error LED will blink sporadically.
4. If the BERT test indicates no errors are present, move the "BERT" switch to the "up" position to activate the "511/E" test with periodic errors. If this test is working properly, the Error LED will blink regularly. A
successful 511/E test will confirm that the loop is in place, and that the Line Driver's built-in 511 generator and detector are working properly.
5. If the remote BERT test indicates that errors are present, but the local analog loopback BERT tests showed that both Line Drivers were functioning properly, there is probably a problem with the twisted-pair
communication line connecting the two modems. A common problem is improper crossing of the pairs. Also, check the cable's pinning and continuity.
USING THE V.52 BERT TEST INDEPENDENTLY:
The Multi-Function Line Driver can perform its V.52 BERT test independently of the V.54 loopback tests. This requires two operators: one to initiate and monitor the test at the local MFLD, and one to do the same at the remote
MFLD. To use the V.52 BERT test by itself, both operators should simultaneously follow these steps:
1. Move the left-hand top-panel slide switch labeled "BERT" test mode and transmit a 511 test pattern to the other unit. If any errors are present, the receiving modem's Error LED will blink sporadically.
NOTE:
For this Independent test to work properly, the "BERT" switch on both Multi-Function Line Drivers must be set
the same way (that is, moved to the "511" position for this step and to the "511/E" position for the next step).
2. If the BERT test indicates no errors are present, move the "BERT" switch to the "up" position to activate the "511/E" test with periodic errors. If this test is working properly, the receiving modem's Error LED will blink
regularly. A successful 511/E test will confirm that the link is in place, and that the Line Driver's built-in 511 generators and detectors are working properly.
