G.703/G.704 NTU W/V35
18
up, signifying that the link is active. The E1 Link LED is Off when the link
is down.
TD & RD
Glows yellow to indicate an idle condition of Binary “1” data on the
respective terminal interface signals. Green indicates Binary “0” data.
LOS
The Loss of Sync LED lights when the unit loses synchronization with the
incoming signal. This may happen when there is a framing mismatch or a
loss of signal. In unframed mode, the LOS LED monitors the status of the
transmit clock.
ER
The error LED indicates various error conditions, including framing bit
errors, excessive zeros, controlled slips, severe errors, or bit errors
(when sending V.52 test patterns). When sending a test pattern, the LED
will remain lit if the unit does not receive the identical pattern. When it
receives the correct pattern, the LED will turn off. If error insertion is on,
the LED will blink once a second if everything is operating properly.
TM
(Active Yellow) Solid Yellow indicates an Active Test Mode. The unit may
be placed in test mode by the local user or by the remote user.
4.9 Loop (V.54 & Telco) Diagnostics
The MT335A offers three V.54 loop diagnostics. Use these diagnostics to test the
NTU and any communication links. These tests can be activated via the front
panel switches or via signals on the MT335A serial port interface.
4.9.31 O
PERATING
L
OCAL
L
OOPBACK
(LL)
The Local Loopback (LL) test checks the operation of the local MT335A, and is
performed separately on each unit. Any data sent to the local MT335A in this test
mode will be echoed (returned) back to the user device (i.e., characters typed on
the keyboard of a terminal will appear on the terminal screen).
