24
IDSL LINE DRIVER W/V.35 OR X.21
Figure 5-2. Local line loopback.
To perform an LLB test, follow these steps:
1. Activate LLB. This may be done in one of two ways:
Move the front-panel toggle switch up to “Local.”
Raise the LLB signal on the interface.
Once LLB is activated, the IDSL Line Driver transmitter output is connected
to its own receiver. Data is also looped back to the line. The TM LED should
be lit.
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 5.4
. If the
BER test equipment indicates no faults, but the data terminal indicates a fault,
follow the manufacturer’s checkout procedures for the data terminal. Also,
check the interface cable between the terminal and the Line Driver.
5.3.2 R
EMOTE
D
IGITAL
L
OOPBACK
(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 returned back to
the originating device. For example, characters typed on the keyboard of the local
terminal will appear on the local terminal screen after having been passed to the
remote Line Driver and looped back.
LLB
initiated
