363-206-285
Circuit Pack Descriptions
Issue 3 June 2001
7-45
General Description of Operation 7
Figure 7-18 provides an overall block diagram of the HDSL circuit pack. The BBF8
circuit pack provides an HDSL interface capability on the DDM-2000 OC-3
Multiplexer. HDSL is an access technology that allows the transport of DS1
payloads over metallic twisted pairs. This technology performs an inverse
multiplexing function which splits the DS1 payload into two 784 Kb/s data streams.
These two data streams are combined at the far-end to reconstruct the original
DS1 payload.
HDSL is a point-to-point transmission technology between two nodes. One of the
nodes (master) is responsible for establishing communications over the
PairGain
proprietary embedded operations channel (EOC). The EOC is required for
synchronizing the two HDSL data streams as well as providing OAM&P between
the two nodes. The other node (slave) may only retrieve or view these parameters.
In each pair of HDSL nodes there must be one master and one slave.
The HDSL signal format used by the BBF8 is compatible with
PairGain
HDSL
equipment. Since the BBF8 circuit pack does not provide line powering, the far-
end
PairGain
HDLS equipment must be externally powered.
Detailed Description of Operation 7
Transmission Circuitry 7
The BBF8 fits into a low-speed slot and provides two, four-wire (2 pair) HDSL
interfaces. These interfaces are compatible with
PairGain
HDSL equipment which
may be located up to 12,000 feet away. A 2B1Q line code is used on each
transmission pair. Each interface provides a full DS1 payload capacity which is
mapped to a SONET VT1.5. The HDSL overhead is in a
PairGain
proprietary
format and can only be terminated by equipment capable of processing this
information. As with the BBF1B (Quad DS1) circuit pack, an MXRVO must be
used in the DDM-2000 OC-3 shelf to perform a VT cross-connect function. Once
in SONET, the DS1 payload is treated as a normal DS1.
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