User manual

Testing the System
Campus-RS Fractional Interface Card User Manual 7-5
V.54 Loopback Support
The Fractional Interface Card supports V.54-compliant loopbacks, which
enable initiation of loopback tests from a V.54-capable host device. Before
you can use V.54 loopbacks, you must enable V.54 loopback support. To
enable V.54 loopback support through the LCD menu, see “Enabling V.54
Loopback Support” on page 4-22. See “Enabling V.54 Loopback Support” on
page 5-31 to enable V.54 loopback support through an ASCII terminal.
The V.54 support function is implemented through the following control
signals on the data port:
• LL Signal (input): When the LL (local loopback) input is activated by
the host device, the Fractional Interface Card initiates a Local to Local
loopback as described on page 7-2. The Fractional Interface Card also
turns on the TM output signal to provide confirmation of the loopback.
The TM signal and Local to Local loopback remain active until the LL
signal is turned off.
• RL Signal (input): When the RL (remote loopback) input is activated
by the host device, the Fractional Interface Card initiates a Remote to
Local loopback as described on page 7-3. The Fractional Interface Card
also turns on the TM output signal to provide confirmation of the
loopback. The TM signal and Remote to Local loopback remain active
until the RL signal is turned off.
• TM Signal (output): The TM (test mode) signal is activated by the
Fractional Interface Card in response to activation of an LL or RL signal.
The TM signal is also activated when any other loopback is initiated from
the LCD, ASCII terminal, or V.54 control signals from the remote unit.
The TM signal indicates to the local host device that a loopback test is
active, regardless of how the test was initiated.
During normal operation, when no loopback is active, all three signals are off.
When a V.54 loopback is in effect, the LL and RL input signals cannot be on
at the same time. For example, when the RL signal is active, the LL signal is
ignored.