150-231-185-05, Revision 05
Appendix B - Functional Operation
HLU-231 List 8E
September 13, 1999
59
A
PPENDIX
B - F
UNCTIONAL
O
PERATION
PairGain HDSL technology provides full-duplex services at standard T1 rates over copper wires between an HLU
and an HRU, which comprise one HiGain system. HiGain systems use PairGain 2-Binary 1-Quartenary (2B1Q)
HDSL transceiver systems to establish two, full-duplex, 784 kbps data channels between the HLU-231 and a
remotely located HDU or HRU. This provides a total capacity of 1.568 Mbps between the two units.
A block diagram of the HLU-231 is shown in
. The HLU-231 receives a 1.544 Mbps DSX-1 data stream
from the DSX-1 digital cross connect interface. The HLU-231 contains a DS1 frame synchronizer controlled by
an 8-bit microprocessor that determines the type of framing on the DS1 stream and synchronizes to it. The
HLU-231 recognizes Superframe (SF), including D4, or Extended Superframe (ESF) framing. When the data is
unframed, the HLU-231 arbitrarily defines a frame bit.
Figure 29.
HLU-231 List 8E Block Diagram
T
IMING
The low loop wander (0.3 UI max) of an HLU-231, when used with compatible doublers (HDU-409,
HDU-404 or HDU-407) and remote units (HRU-402 or HRU-411), allows the circuit to be used in all critical
timing applications, including those that are used to transport Stratum 1 timing.
