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Data Cards 17-11
OCU-DP Card OCU-DP Card User Screens and Settings
LB DET
The Loopback Detection setting determines how the system responds to latching loopback
commands from remote equipment. The OCU-DP reacts only to the in-band DDS format
loopback commands for Channel Loop, OCU Loop and DSU Loop. The Loopback Detection
setting does not affect local loopback commands from the local control terminal. The settings
are off, on and w/to (on with time out).
The off option causes the system to ignore all remote loopback commands. The on option
causes the system to monitor for DDS format loopback commands from the remote
equipment. If the system detects a loopback command, it loops the data back until the remote
equipment sends a stop loopback command. The time-out (w/to) option is the same as the on
option, except that after 10 minutes the system automatically releases loopbacks commanded
by the remote equipment.
When using the OCU-DP port for a clear-channel, 64 kbps circuit in DS0A mode, you should
set the loopback detection to off to prevent unintentional loopback activation.
There are four sequences required for loopback. Each sequence is a given byte that is repeated
several times. In-between the sequences there is some allowance for stray bytes but only
related bytes. If enough illegal bytes are detected before the proper ones, then any progress
toward loopback is lost. The probability calculation with the following assumptions is: (a) the
rate is 64K (any other rate is less likely since bit 8 is restricted); (b) proper bytes and illegal
bytes come in randomly but the proper bytes are 10 times more likely than standard gaussian
data. The false detect probability is 6 E-18 or about 600,000 years average between false
loopbacks.
17.3.2 Performance Data Screen
If "majority vote" or "BCH" error correction is enabled on the OCU-DP 2 Card, the system
will support performance monitoring of data traffic. The Performance Data Screen is accessed
by selecting one of the two ports from the OCU-DP Card Main Screen and pressing "p" (Perf).
A typical Performance Data Screen is shown in Figure 17-9
2
. However, note that error
correction and performance data are not supported on the OCU-DP 5 Card.
If the BCH method of error correction is selected, the OCU-DP card will monitor data traffic
coming in from the T1 network and use the BCH polynomial values that accompany the data
to log the number of errors and to try and correct such errors. Any data errors that are observed
are considered "input" data errors and contribute to the input error statistics, including Input
Errored Seconds (IES), Input Severely Errored Seconds (ISES), and Input Consecutive
Severely Errored Seconds (ICSES).
Depending on the severity of the input errors, the BCH algorithm may be able to correct the
data prior to transmitting it over the four-wire DDS circuit. If an error is so severe that it cannot
be corrected, then it will also be logged as an "output" data error and will increment the Output
Errored Seconds (OES), Output Severely Errored Seconds (OSES), and Output Consecutive
Severely Errored Seconds (OCSES) counters.