Section 150-319-124
Revision 03
Page 3
deploying service in advance of fiber-optic
transmission systems. With the HiGain system,
service can be provided within hours. Fiber optic
systems can be installed at a leisurely pace and cut
over from the installed HiGain system when
convenient to do so. The installed HiGain system can
then be easily removed and utilized elsewhere.
3. FUNCTIONAL OPERATION
3.01
The HiGain system utilizes PairGain 2-Bit
1-Quartenary (2B1Q) HDSL transceiver systems to
establish two full duplex 784 kbps data channels
between the HLU-319, List 2D and a remotely
mounted HRU-412 HiGain Remote Unit. This
provides a total capacity of 1.568 Mbps between the
two units.
3.02
A block diagram of the HLU-319, List 2D is
shown in Figure 2. The HiGain HLU-319, List 2D
receives a 1.544 Mbps DS1 data stream from the
DSX-1 digital cross connect interface. The HLU-319,
List 2D contains a DSX-1 frame synchronizer
controlled by an 8-bit microprocessor that determines
the type of framing on the DS1 stream and
synchronizes to it. The HLU-319, List 2D recognizes
Super Frame (SF) (including D4) or Extended Super
Frame (ESF) framing. When the data is unframed,
the HLU-319, List 2D arbitrarily defines a frame bit.
3.03
The HLU-319, List 2D contains a multiplexer
that generates two parallel 784 kbps data streams.
The data streams contain HDSL frames that are
nominally 4704 bits (6 milliseconds) in length. The
HDSL frames contain a 14-bit Frame Sync Word
(FSW), 6-bit Cyclic Redundancy Check (CRC), 21-bit
operations channel and DSX-1 payload. The DSX-1
stream is separated into two parallel streams that
comprise the payloads of the HDSL channels. The
HLU-319, List 2D allocates the DS0 time slots
according to the version of HRU-412 to which it is
connected. Older version HRUs require the odd DS0
time slots allocated to loop 1 and the even DS0 time
slots to loop 2. Newer versions allocated DS0 time
slots 1 through 12 to loop 1, and time slots 13 through
24 to loop 2. The 8 kbps frame bits of the DSX-1
stream are included on both HDSL channels. The two
formatted HDSL channels are passed to the HDSL
transceivers which 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.
Figure 2. HLU-319, List 2D Block Diagram. PairGain’s HDSL technology provides full duplex services at standard T-1 rates
over copper wires between an HLU and an HRU, which comprise one HiGain system.