Operation
DMD2401 LB/ST L-Band Satellite Modem and ODU Driver
3-2
TM075 – Rev. 1.3
3.2.2 SCPC Point to Multi–Point Links in a Broadcast Application
A broadcast application might involve the necessity of sending continuous or intermittent data
from one source and “broadcasting” the information to many remote locations. For instance,
constant pricing information and updates may be sent by a central location to many store
locations. There may be minor return information from the remotes acknowledging receipt.
Another broadcast application could be transmitting background music from a central location to
many store sites. In this case, there would be no return path.
The topology of the network in both of these broadcast examples would typically be called a
“Star” network. As shown in the Figure below, the shape of the configuration is drawn with the
central “Hub” as the center of the star and the remotes as points of the star. In both cases the
transmit frequency and other parameters are shared by the receiver of all the remotes.
Figure 3-2. Star Network Configuration
3.2.3 DAMA (Demand Assigned Multiple Access)
Suppose that a telephone network with a virtual switch between modems carrying digitized voice
information is to be simulated. We might use a central computer to assign a pair of frequencies
for any conversation and send this connection information to the proper sites to set up the
connection. In this application, a new network configuration is usable. That is a “Mesh” network
where any of the voice modems at any site can be programmed to link with any other modem.
The resulting link diagram looks like a mesh of interconnects.
Since the frequencies can be assigned on demand, the network is then called “Demand
Assigned, Multiple Access,” or DAMA.
3.2.4 TDMA (Time Division Multiple Access) Remote Site Application
In a TDMA network, the central Hub continually transmits a stream of outbound data containing
information for multiple remote sites, while the remote sites transmit back to the Hub on a timed
basis. Each of these remotes is said to “burst” its information back on a specific frequency. This
may be the same inbound frequency for all sites. Each of the remotes is responsible for
accessing its own information from the outbound data stream by reading the address assigned to
specific parts of the data. The TDMA network usually looks like the Star network shown in
Figure 3-2.
