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2-4
Overview
Multiplexing the OOB Data
The packet multiplexer combines OOB data from the Ethernet and serial input ports into a
single MPEG-2-compliant transport multiplex, and then routes this multiplex to the RF
modulator. The multiplexer can also accept input data from special internal sources (for
example, PID 0 and PID 1 control data) if necessary.
CAUTION
The aggregate input rate of all data to be combined into the RF output must not exceed 2.005 Mbps. If the rate is lower
than 2.005 Mbps, the multiplexer will add null packets to achieve the correct data rate. If the aggregate input rate is
higher than 2.005 Mbps, the multiplexer will drop packets.
The main destination for most OOB data is the RF modulator; however, the multiplexer can
route data to other output destinations. Each input packet stream can be routed to up to three
different output destinations. Table 2-2 lists the available destinations:
Table 2-2
Multiplexer output destinations
Destination
Description
The RF modulator uses QPSK modulation to convert an MPEG-2-compliant transport
RF modulator
multiplex into a 1.5 MHz-wide RF signal with a center frequency from
71 through 129 MHz. Data directed to this destination is output from the
IF OUT
Serial data ports
Data directed to a serial data port is output as a serial datastream. The serial data
ports are valid destinations only when configured as output or bi-directional ports.
User Datagram
Data directed to a UDP port is output as a serial datastream. The UDP connections
are valid destinations only when configured as output ports. A legal UDP port number
Protocol (UDP)
must be assigned to each connection, and the IP address of the receiving device must
connections over
be configured.
the Ethernet port
Null port
The null port is a conceptual destination equivalent to routing a packet to nowhere
(that is, discarding the packet).
Because of the number of possible input sources and output destinations, the OM 1000 relies on
a collection of data-handling specifications called PID maps to support the proper multiplexing
and routing of data through the packet multiplexer. One set of PID maps is defined for each
input port to control how the multiplexer handles packets from those streams. Within the set
for a port, a single PID map controls the handling of one packet stream, and each set includes a
default PID map to control the handling of packet streams having no explicit PID mapping.
The multiplexer uses a queuing scheme to transfer packets from input ports to output buffers.
Each destination has a dedicated queue composed of multiple data buffers set up to handle
packets from particular input packet streams. As an input packet enters a given input port, the
packet multiplexer reads the stream PID map and transfers the packet to the correct output
destination queue. To generate the output multiplex for a given destination, the multiplexer
extracts packets from the destination queue by taking one packet from each buffer in a
round-robin fashion.
OM 1000 Installation and Operation Manual
connectors on the OM 1000 back panel.
and
RF OUT
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