TTC T-BERD 107A, Reference Manual

Page: 72 / 261

SECTION 3
3-33
INSTRUMENT
DESCRIPTION
Pre-Existing Loop LED
23
This red LED illuminates when a pre-existing loop
is detected. The Pre-Existing Loop LED illumi-
nates and remains illuminated for five seconds
during an in-band loop-up attempt when an in-band
loop-up code is detected within one and a half
seconds from the start of loop-up code transmis-
sion. When a pre-existing loop is detected, the
transmission of the in-band loop-up code is imme-
diately halted, and the
LOOP UP switch LED is
extinguished.
ERR INS Switch
24
This switch inserts a single logic error and a single
BPV into the transmitted data stream each time it is
pressed. When performing out-of-service tests, use
the
ERR INS
switch to ensure continuity of the
system.
Logic errors and BPVs can be inserted in all transmit-
ted signals, except when T1 LLB mode is selected.
Logic errors and BPVs are inserted without regard to
B8ZS coding sequences. This may cause the same
error multiplication (one inserted error causing mul-
tiple errors) that occurs on a repeatered span. Errors
are randomly inserted on data bits (99.48% probabil-
ity) and frame bits (0.52% probability). If the inserted
error overwrites a data bit while in T1 ESF, it will
cause a CRC error.