Section 150-232-100
Revision 01
Page 16
6. PROTECTION SYSTEM OPTION SETTINGS
6.01 When the two HLU-232 plugs are to be used for the Protection function, the configuration switch on the HSA-
232 Shelf Adapter must be set to PROTECT. For more details, refer to the HSA-232 Technical Practice #100-232-
100. The configuration switch on the HRE-422 must also be set to PROTECT. For more details, refer to the HRE-
422 Technical Practice #100-422-100.
6.02 Table 3 lists the user option settings that are unique to the Protection System mode of operation. All of these
options are settable on the HLU-232 being used for the protection circuit. Only the BER Threshold and BER Interval
are settable on the HLU-232 being used for the primary circuit. The Protection Mode can be set by the front panel
MODE and SEL buttons. The rest of the options can only be set using an ASCII terminal connected to the front
panel RS-232 maintenance port.
6.03 Auto Protect (APRO) is the default mode of the Protection configuration. In this mode the protect HLU-232
monitors the performance of the Primary circuit and automatically forces a switchover from the Primary system to the
Protect system if any of the following events occur:
1. A minor alarm occurs in the primary system. These include a LOSW, H1(2)ES or MAL1(2). Since both the
Primary & Protect circuits use the same T1 input, an LLOS or RLOS condition usually affects both circuits.
This prevents a switchover from occurring because the Protect circuit is affected by the same problem as the
Primary. An LLOS or RLOS will only cause a switchover in the rare event that the condition is only detected in
the Primary and not the Protect circuit.
2. The user defined BER threshold is exceeded in the Primary system. The BER switching threshold can be set
to one of the four values shown in Table 3. A BER bit error is defined as either an HDSL CRC or FEBE (far
end bit error) in either of the two HDSL loops. An HDSL CRC error occurs when the bit pattern of the received
HDSL frame is different from that of the transmitted frame. A FEBE means that a CRC error occurred in the
HDSL receiver at the other end of the loop. A CRC error implies at least one or more HDSL bit errors. Since
each HDSL loop transmits 784 kbps, a BER of 10
-4
implies at least 4704 CRC errors per minute. The BER
threshold is satisfied only when the selected threshold is exceeded for the BER measurement interval, which
can also be selected by the user. Since fewer errors are required to exceed the lower BER rates, more time is
required to compute an accurate BER at these lower rates. The three possible intervals are 5, 10 & 15
minutes. The default measurement intervals for each BER threshold and the number of CRC errors required in
each interval is:
10
-4
: 5 minutes (23,520 CRC errors)
10
-5
: 5 minutes (2352 CRC errors)
10
-6
: 10 minutes (470 CRC errors)
10
-7
: 15 minutes (70 CRC errors)
6.04 Switchover causes a minor alarm in the Protect circuit which is displayed as ALRM PROT on its front panel
display. Once switchover has occurred, the Protect line unit continues to monitor the integrity of the failed Primary
circuit. It will revert back to the Primary circuit when all of the following conditions are satisfied:
1. The user selected Minimum Hold-in Time has expired.
2. The Primary circuit has 10 contiguous seconds of error free HDSL operation.
3. The Primary circuit has a BER performance at least 10 times better (lower) than the selected threshold, up to
a limit of 10
-7
4. The Primary circuit margin is at least 3 dB greater than the programmed threshold, up to a limit of 15 dB.
5. The user-selected Lock-In thresholds (maximum switchovers, switch interval, lock-in hours), if exceeded, have
also been satisfied.
