41
Once LLB is activated, the Card’s 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 5.2.3
. 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 Card.
5.2.2 R
EMOTE
D
IGITAL
L
OOPBACK
(RDL)
The Remote Digital Loopback (RDL) test checks the performance of both the
local and remote Cards and the communication link between them. Any characters
sent to the remote Card in this test mode will be returned back to the originating
device (see Figure 5-3). 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 Card and looped back.
Figure 5-3. Remote digital loop.
IMPORTANT
Do not send a 511 test pattern from the test equipment when you
connect external test equipment to the 2-WIre IDSL Line Driver Rack
Card.
To perform an RDL test, follow these steps:
1. Activate RDL. This may be done in three ways:
a) Move the front-panel toggle switch to the left to “Remote.”
b) Raise the RDL signal on the interface (see
Appendix C
).
c) Set remote loopback from the VT100 screen.
CHAPTER 5: Operation
Local 2-Wire
IDSL Line Driver
Remote 2-Wire
IDSL Line Driver
RDL
initiated
