Specifications

Chapter 6 Troubleshooting and Diagnostics Installation and Operation Manual
6-20 Testing the Unit FCD-E1LC Ver. 1.0
or 2, or the sublink). If you already specified timeslots for BER testing (by means
of the DEF BERT ML command), the FCD-E1LC will automatically use the timeslots
specified for BER testing, if such definition is present
The loopback is activated and deactivated by transmitting special sequences for
approximately 2 seconds:
• The FCD-E1LC sending the sequence reports this state as TX INBAND
• The FCD-E1LC receiving the sequence reports this state as RX INBAND.
You can use the standard FT1/FE1 RDL inband sequence specified in ANSI
(T1.403), or select a pattern of your own.
• With the INBAND_LOOP_PATTERN is set to RDL, when the LP INBAND ML
command is activated, the generator sends the standard RDL sequence.
• With the INBAND_LOOP_PATTERN is set to USER, you can specify a desired
string, consisting of 1 to 8 bits. The generator then repetitively sends this
string.
After the loopback is activated in response to the detection of the appropriate
sequence, the local FCD-E1LC starts returning the activation sequence toward the
activating unit, where it is detected by the sequence evaluator. This confirms the
activation of the requested loopback.
To deactivate the loopback (in response to a CLR LP INBAND ML command), the
generator sends the corresponding loop deactivation sequence (either RDL or the
user-configured string). The deactivation is confirmed when the reception of the
deactivation sequence stops.
BER Testing (LP BERT ML)
The BER test subsystem comprises a test sequence generator and a test
sequence evaluator (the same circuits used by the inband-activated loopback
function, which were described above). During the test, the main link payload
data is replaced by a pseudo-random sequence generated by the test sequence
generator. The transmitted data is returned to the test sequence evaluator by a
loopback activated somewhere along the main link signal path.
The evaluator synchronizes to the incoming sequence, and then compares the
received data, bit by bit, to the original data sequence and detects any difference
(bit error). The test results are presented on the supervision terminal (see the
DSP BERT ML command in Appendix D ).
To calibrate the system, the user can inject errors at a selectable rate.
When two FCD-E1LC units are operated in a link, it is also possible to perform the
test by activating the BER test subsystems at both ends of the link at the same
time and configuring both subsystems to use the same test parameters. In this
case, it is not necessary to activate a loopback, because the BER test subsystem
can process the sequence transmitted by the far end subsystem in the same way
as its own sequence. This avoids the need to activate a loopback when the
loopback itself may alter the operating conditions on the tested path (for
example, in certain cases a loopback may cause switching to an alternate clock
source and thus affect the flow of timing information within the network).
The BER test is used for two purposes: