150-402-102-01, Revision 01
Appendix A: Additional Technical Information
HRU-402 List 2
July 27, 1998
45
F
EATURES
The following describes additional information on some of the features
included with the HRU-402 List 2.
Bipolar Violation Transparency (BPVT) and Bit Error Rate
(BER) Options
The HRU-402 List 2 and its associated line units improve compatibility with
Data Link Control (DLC) feeder applications due to T1 BPVT transmit
capability between 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 BPVTs in its T1 input. Standard HDSL systems correct
input T1 BPVTs and thus prevent them from being detected by DLC
terminals to which they are connected. The HRU-402 List 2 and its associated
line units remove this limitation and become BPVT transparent by detecting
and counting input BPVTs at each end and then replicating them at the distant
end T1 output port.
In addition, the CRCs in each direction of every HDSL loop of each span are
also counted and added in with the BPVT count to produce a Total Error
Count (TEC). TEC indicates the integrity of both the T1 and HDSL paths. A
TEC in each direction is calculated every second by adding the number of
BPVTs to the number of HDSL CRCs in that direction. The maximum TEC
count is 12000. This TEC number is converted into BPVTs at the distant end
during the following second at a rate of 1 BPVT every 128 T1 bits up to a
maximum of 12000 (BER=7.7x10
-3
). This maximum rate is more than
adequate since it exceeds the maximum 10
-3
BER required by most DLC
systems.
The BPVT transparency option is controlled by the BPVT user option, which
can be enabled (ENA) or disabled (DIS).
This BPVT is a “smart” option in that it is only available if the
HRU-402 is connected to an HLU-231 List 8x, HLU-319 List 5x,
or HLU-388 List 5x.
