40
2-WIRE IDSL LINE DRIVER RACK CARDS
• ER glows red to indicate the likelihood of a bit error in the received signal.
During the 511 or 511E test, ER flashes to indicate that the test-pattern
detector has detected a bit error.
• TM glows yellow to indicate that the Card has been placed in test mode. The
unit can be placed in test mode by the local user or by the remote user.
• NS (No Signal) glows red to indicate that the local Card has not yet connected
with the remote Card.
5.2 Test Modes
The 2-Wire IDSL Line Driver Rack Card offers two proprietary loopback test
modes, plus a built-in V.52 BER test-pattern generator, to evaluate the condition of
the modems and the communication link. These tests can be activated physically
from the front panel or via the interface.
5.2.1 L
OCAL
L
INE
L
OOPBACK
(LLB)
The Local Line Loopback (LLB) test checks the operation of the local Card and is
performed separately on each unit. Any data sent to the local Card in this test
mode will be echoed (returned) back to the user device (see Figure 5-2). For
example, characters typed on the keyboard of a terminal will appear on the
terminal screen.
Figure 5-2. Local line loopback.
To perform an LLB test, follow these steps:
1. Activate LLB. This may be done in one of three ways:
a) Move the front-panel toggle switch to the right to “Local.”
b) Raise the LLB signal on the interface (see
Appendix C
).
c) Set local loop from the VT100 screen.
LLB initiated
