Comtech EF Data MD2401 - Manual (Page 28)

MD2401 L-Band Multi Demod Installation and Operation Manual Theory of Operation
MN-MD2401 3–4
Revision 7
3.2.3 DAMA (Demand Assigned Multiple Access)
If a telephone network is to be simulated with a virtual switch between demodulators carrying
digitized voice information. A central computer might be used 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 called a “Mesh” Network is required. Any of the
voice demodulators at any site can be programmed to link with any other demodulator. The
resulting link diagram looks like a mesh of interconnects.
Since the frequencies can be assigned on demand, the network is 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 described above.
The MD2401 is specifically designed to be usable as the remote site Demodulator of a TDMA
network when coupled with a proper “Burst” Demodulator at the hub site.
3.3 3.2 Clocking Options
The Demodulator supports a number of different clocking options that can be recovered from the
satellite or the terrestrial links. The various clocking options allow users to determine which clock
will best fit their applications. Figure 3-4 gives an overview on how the modem processes the
various clocks for the Rx Buffer Clock source.