PairGain HiGain HLU-319 Manual page 11

150-319-142-01
convert them to the 2B1Q format on the HDSL lines. The 2B1Q line code is
designed to operate in a full-duplex mode on unconditioned pairs. The
transceiver echo canceler and adaptive equalizer receive the signal from the
remote end in the presence of impairments and noise on the copper pairs.
The received HDSL channels are processed by the transceiver and then
passed on to the HLU-319 List 4B demultiplexer module. The demultiplexer
provides frame synchronization for each of the two HDSL loops. The
demultiplexer and HDSL transceivers work under control of the HLU-319
List 4B microprocessor and compensate for data inversions caused by tip-ring
reversals and loop swaps caused by pair reversals. The HiGain system allows
for tip-ring or pair reversals, but does not allow split pairs. By synchronizing
to the Frame Sync Word (FSW) of each loop, the demultiplexer can
reconstruct the original 1.544 Mbps DS1 stream from the payloads of the two
HDSL loops. The CRC fields on the HDSL streams allow the HLU-319 List
4B to determine if errors are present on the channel due to excessive
impairments on the HDSL pairs or excessive impulse or crosstalk noise.
The demultiplexer removes data link messages from the HDSL loops and
passes them to the microprocessor. This mechanism allows operations
messages and status to be exchanged between the HLU-319 List 4B and the
remote HRU-412 List 8B.
The reconstructed HDSL data is buffered in a first-in-first-out (FIFO) buffer
within the demultiplexer. A frequency synthesizer, in conjunction with the
FIFO buffer, regulates the output bit rate and reconstructs the DSX-1 clock
frequency-locked to the DS1 clock at the remote end. The HiGain system
operates at T1 rates of 1.544 Mbps with up to ± 200 bps of offset.
A DSX-1 interface driver converts the receive data to an Alternate Mark
Inversion (AMI) or Binary Eight Zero Substitution (B8ZS) format. The
DSX-1 equalizer is programmable to five different lengths, as determined by
the distance between the HLU-319 List 4B and the DSX-1 interface. This
provides CB-119 specification compliant pulses at the DSX-1 interface over
a range of 0 to 655 feet of ABAM-specification cable.
The HLU-319 List 4B contains a main power supply that converts -48 Vdc
power to voltage for the HLU-319 List 4B circuitry.
The female 9-pin (DB-9) Craft (RS-232) port, on the front panel, provides
access to HiGain system configuration, provisioning, and performance
monitoring.
HLU-319 List 4B
December 22, 1997
PairGain Engineering - Plant Series
Revision 01
5