Specifications

5.3.2 R

EMOTE

IGITAL

OOPBACK

(RDL)

The Remote Digital Loopback (RDL) test checks the performance of both the

local and remote Multi-Function Line Drivers, and the communication link

between them. Any characters sent to the remote MFLD 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 Multi-Function 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”—see Section 3.3). Once

RDL is activated, the remote MFLD’s receive input is connected to its

own transmitter. The Test LED should light on both MFLDs.

2. Verify that the DTE attached to the local MFLD 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

Multi-Function 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 Multi-Function 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 (see Table 4-1 on page 17) and continuity. If you still get

errors and can’t find the cause, call Black Box for technical support (see

Section 6.1).

CHAPTER 5: Operation and Diagnostics