FE1 Fiber Modem Installation and Operation Manual
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Optic interface receiving timing (optic interface originated from the clock,
S5.1=OFF，S5.2=ON):
the sending timing is optic interface receiving timing, and the received data, after
buffering, is synchronized with optic interface receiving timing. Under this timing
mode, local time slot setting can automatically track the opposite time slot setting.
Local main timing (S5.1=ON, S5.2=ON): the sending timing is of local crystal
oscillation, and the received data, after buffering, is synchronized with local timing.
5.3.2 Settings of loop back test and pseudo-random code test
S5.5～S5.8 of coded switch S5 are used for setting the loop back test and pseudo-
random code test. S5.5 is local loop back control （LLOOP）and optic interface is
directly looped back to E1 interface. “OFF” indicates normal operation; “ON”
indicates local loop back test. The default is “OFF”. It is used for testing whether
local device is in normal operation.
Local Loop back Schematic
S5.6: local digital loop back control (DLOOP). “OFF” indicates normal operation;
“ON” indicates local digital loop back. The default is “OFF”. With a loop back
from local E1 interface to optic interface, it is used for testing whether the
remote device and optic line are in normal operation.
Local Digital Loop back
S5.7: “OFF” indicates normal operation；“ON” indicates command remote loop
back. The default is “OFF”. As this command must be sent through E1 line to
remote end for validness, it will become invalid at the following two cases: ①
the remote end is not FE1 Fiber Modem remote device; ② FE1 Fiber Modem
is working at a non-framing status, at this moment all time slots of E1 are used
for data transmission at a rate of 2048Kbps. Through a sending of loop back
command from local device to remote device, the command remote loop back
is achieved.
