
150-231-184-05, Revision 05
Provisioning
HLU-231 List 8D
October 25, 1999
23
Equalization Option
Equalization is the configuration of system transmission characteristics within specified limits. An adaptive
equalizer inserts a frequency-shaped loss that corresponds to an equivalent addition of an appropriate cable length.
By simulating the additional cable loss necessary for correct operation, the equalizer compensates for a range of
variation in transmission path characteristics.
BPVT Option
The HLU-231 List 8D improves HiGain’s compatibility with Digital Loop Carrier (DLC) feeder applications
because of its ability to transmit T1 BPV occurrences between its T1 interfaces. This feature is required to support
protection switching in DLC applications. Each DLC terminal must be able to monitor the integrity of its Receive
T1 payload and then switch to the protect line when the integrity of the path drops below specific user-selected
limits. An essential requirement of this feature is the need for each DLC terminal to detect BPVs in its T1 input.
Standard HDSL systems correct T1 BPVs at the input and prevent them from being detected by the DLC terminals
to which they are connected. The HLU-231 and its associated remote units remove this limitation and become
BPV transparent by detecting and counting input BPVs at each end and then replicating them at the T1 output port
of the distant end. When the BPVT option is Enabled (ENA), the Fast LOSW feature reports LOSW conditions
within approximately 2 seconds. When the BPVT option is Disabled (DIS), LOSW conditions may take up to 10
seconds.
In addition, the CRCs in each direction of every HDSL loop of each span are counted and added in with the BPV
count to produce a Total Error Count (TEC) that indicates the integrity of both the T1 and HDSL paths. A TEC
in each direction is calculated each second by adding the number of BPVs to the number of HDSL CRCs in that
direction. The maximum TEC count is 12,000. This TEC number is converted into BPVs at the distant end during
the following second at a rate of 1 BPV every 128 T1 bits up to a maximum of 12000 (BER=7.7 x 10
-3
). This
maximum rate is more than adequate since it exceeds the maximum 10
-3
BER required by most DLC systems.
BER Option
The BER option also uses this (BPV/CRC) TEC to generate an Alarm, if enabled. The HLU combines the
1-second TEC counts in both directions for the last 60 seconds. It uses this 1-minute Total System Error Count
(TSEC) to generate an alarm if it exceeds the selected BER threshold (1E-6 or 1E-7) as follows:
•
BER option = 1E-6. Alarm is generated if TSEC > 92.
•
BER option = 1E-7. Alarm is generated if TSEC > 9.
If initiated, the alarm clears when the TSEC drops below its associated threshold count. For dribbling errors, the
alarm can come and go in intervals as short as 1 second. Alarms due to bursty impulse noise transients usually
require the full 60 seconds or longer to clear depending on the frequency of the transients. This BER option is
always present in any line unit circuit since it is independent of other versions of HiGain modules in the circuit.
When connected to an HRU, other than the HLU-402, HLU-406, or HLU-411, only the BVPs detected by the
HLU are included in the TBC. The BPVs at the HRU are not counted.
When BPVT is enabled in systems with four or fewer doublers, the response time to an HDSL
LOSW is reduced to approximately 70 ms (milliseconds), which gives DLC terminals time to
react and avoid dropped calls. This is known as the “Fast LOSW” feature.