User`s guide

Functional Overview
5–2 MS-4900, Rev. A
The NCC:
Input and
Output
Input to the NCC consists of data feeds arriving through the access network. This
can be data originating from a remote or local computer. Some of this data is
processed in the statistical multiplexer, commonly called a stat mux. The stat mux
assembles that data into a series of packets. The packets contain information about
the data, such as message length, source, specific output destination, encryption or
compression keys, as well as the data itself. Packets are then placed into link blocks,
to which are also added Reed-Solomon type FEC bits.
The stat mux data, control channel information, and other data passing directly from
the access network, moves to the time-division multiplexer, or TDM. The TDM
combines and orders the data into a single aggregate data stream. The TDM sends
this data stream to a modulator to be converted into an analog signal, ready for
uplinking to a satellite. Data may be uplinked from the NCC itself or transmitted to
another site for modulating and uplinking. Figure 5-1 illustrates this network. The
top half of the figure shows NCC side, at which data from multiple sources is
assembled and “packaged” for uplinking to the satellite. The lower half of the figure
shows the receiver, where the transmitted data is disassembled and processed as
necessary, and output to an end user’s server or an individual computer.