Theory Of Operation - Cabletron Systems SWPIM-DDS Installation Manual

THEORY OF OPERATION

The DDS interface consists of the following: framer/transceiver and line
isolation/protection.
DDS Framer/Transceiver
The SWPIM-DDS provides the framing and transceiver functionality for
DDS-PRI and DDS-CC (Clear Channel).
DDS-PRI - DDS-PRI is a full duplex 56k link. There is no framing in the
loop data, therefore the loop speed is also 56k. Data on the loop is a
simple serial data stream:
----------d1 d2 d3 d4 d5 d6 d7------------
The incoming data is amplified and filtered, checked for Bipolar
Violations, and the differential pair is converted to a single bit stream. In
the conversion, the receive clock is extracted and dejittered. On the
transmit side, the serial data stream is converted to a differential pair and
the proper pulse shaping is provided. These same functions are performed
in each framing mode.
Because there is no frame, alarms and control information are all sent
using Bipolar Violations. The incoming Bipolar Violations are deciphered
and the host platform CPU is alerted. The host platform CPU can then tell
which code is being received. These same codes can also be transmitted
using Bipolar Violations.
DDS-CC is a full duplex 64k link. The Clear Channel (CC)
DDS-CC -
format does not require a framing bit but uses the same format as the
Secondary Channel (SC). The only difference between Clear Channel and
Secondary Channel is that the ninth bit position is used in the primary
channel and not used for control. The loop speed is 72k but the primary
channel rate is 64k.
Data in the loop is in the following format:
----------d1 d2 d3 d4 d5 d6 d7 F d8------------
Where F equals the framing bit. The framing bit repeats itself in the
following format:
101100
SWPIM-DDS Installation Guide
Introduction
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