
150-388-105-05, Revision 05
Appendix B - Functional Operation
HLU-388 List 5
March 25, 2000
61
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-388 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-388 is shown in
. The HLU-388 receives a 1.544 Mbps DSX-1 data stream
from the DSX-1 digital cross connect interface. The HLU-388 contains a DS1 frame synchronizer controlled by
an 8-bit microprocessor. This frame synchronizer determines the type of framing on the DS1 stream and
synchronizes to it. The HLU-388 recognizes Superframe (SF), including D4, or Extended Superframe (ESF)
framing. When the data is unframed, the HLU-388 arbitrarily defines a frame bit.
Figure 29.
HLU-388 List 5 Block Diagram
T
IMING
The low loop wander (0.3 UI max) of an HLU-388 List 5, 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.
G
ROUND
F
AULT
D
ETECT
The HLU-388 has a Ground Fault Detect (GFD) circuit which detects a ground or a resistive path to ground on
any wire of any loop of any span with a nonzero voltage. For low (-140 Vdc) applications, such a circuit is active
during start-up by applying the bipolar voltage to the loops. It deactivates when going to the nominal operation
mode of unipolar negative voltage (0 Vdc and -140 Vdc). The circuit is constantly active during high (±112 Vdc)
applications.
HDSL 1
XCVR
HDSL 2
XCVR
Microprocessor
A
B
106
102
105
101
Tip1
Tip
Ring1
-
+
Ring
HDSL 2
HDSL 1
109
115
110
114
119
104
Frame ground
Management bus
STATUS
Ring
Ring1
Tip
Tip1
-48Vdc
217
DSX-1 XMT
DSX-1 RCV
DEMUX
MUX
Power supply
B
A
Pre-
equalizer
select
T1
framer
MODE
-140V or
± 112V HDSL
line voltage
power supply
(ground isolated)
SEL
RS-232
(front panel)
218, 118
Ground
Fuse alarm
117