2 OVERVIEW
8
Functional Overview
The OM 2000’s primary function is to combine multiple OOB data inputs into a
single datastream that is transmitted over the OOB channel as an RF signal. The OM
2000 also provides additional signal-processing functionality:
Serial data communications
To support other application requirements, the OM 2000
transmits and receives baseband digital data over
various serial data ports.
Emergency alert operation
The OM 2000 can monitor an emergency alert remote
control unit and receive and store special cable terminal
control messages. When a relay closure is sensed, the
special messages are inserted into the OOB data
transmission.
OOB Signal Processing
In converting the OOB data inputs into an RF signal, the OM 2000 performs the
following OOB signal processing functions:
•
Receives the cable terminal control stream and other OOB data from multiple
input sources
•
Multiplexes the information into a single, packet-based, MPEG-2-compliant
transport stream
•
Inserts PID 0 and PID 1 control streams into the transport stream, if necessary
•
Modulates the digital transport stream onto a 1.8 MHz-wide RF carrier using
QPSK modulation
•
Upconverts the resulting signal into an RF output with a center frequency in the
71 through 129 MHz range. (An IF output is available for optional external
upconversion to other frequencies.)
Figure 2-2 shows the typical flow of OOB data from the input port(s) through the
packet multiplexer to the RF modulator:
