150-402-111-02
Overview
HRU-402 List 1A
December 8, 1998
3
BPVT
AND
BER F
EATURES
The HRU-402 and its associated line units improve compatibility with Data
Link Control (DLC) feeder applications due to T1 Bipolar Violation
Transparency (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 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 CRC errors 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 CRC errors 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 (Bit Error Rate[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 only available if the HRU-402 is connected to an
HLU-231 List 8x, HLU-319 List 5x, or HLU-388 List 5x.
