1.1 System Overview

The satellite Network Digital DAMA System is based on the Single Channel Per Carrier (SCPC) and Demand Assigned Multiple Access (DAMA) technology, which provides an effective attractive method to support, thin to medium telephony traffic while reducing the space segment and ground segment costs. Instead of dedicated Point-to-Point links, the system assigns the satellite resources on demand. A much smaller amount of satellite bandwidth can be shared, thus taking advantage of the random and occasional nature of telephony traffic. Since DAMA system assigns bandwidth on a per call basis, full Mesh single hop connectivity is possible.

1.2 Network Architecture

DAMA system contains four different types of carries; one outlink carrier, up to five signaling returnlink carriers, one monitor and control returnlink carrier and multiple traffic carriers. The signal outlink is a continuous Time Division Multiplexed (TDM) 16kb/s carrier broadcast from the NMS to all the channel units in the network. It is used to provide system control, call setup; software downloads along with monitor and control of the entire network. The signaling returnlinks are shared by the entire network and are used to support call requests and status. The channel units share the returnlinks by using an Aloha access scheme with very short 16kb/s bursts. Small networks with less traffic only require one or two returnlinks. As your network grows additional returnlinks can be easily added up to a total of five. With the maximum of five signaling five links the network will support up to 30,000 busy hour calls.

A separate returnlink for Monitor and Control (M&C) allows the Network Management System to monitor very large network without impacting the traffic. The NMS can continuously poll all the idle channel units in the network. Idle channel units are always tuned to the outlink. When a channel unit receives a status request on the outlink, it responds via the M&C returnlink with a short message. This M&C system allows the NMS to monitor and control not only the channel units but also the RF and external hardware as needed.

The typical call setup procedure is as follows

· The caller picks up the phone and dials the number to be called.
· The channel unit associated with the caller receives all the dialed digits, verifies the number against its digits table and sends a short call request message to the NMS via one of the signaling returnlinks.
· The NMS logs the request, compares the number against the routing table, determines what bandwidth is available, what transmit power levels are required and negotiates the appropriate data rates for the satellite link. The call setup information is then sent to the caller and called channel units via the signaling outlink.
· The caller and the called channel units then tune to the assigned frequencies and adjust their data rates and power levels accordingly.
· The satellite link is established between the channel units and a brief handshake takes place.
· The called channel unit then rings the called phone.
From the time the caller channel unit receives the last dialed digit until the called phone rings will typically be less than 2 seconds. This is as good or better than most terrestrial phone systems and significantly better than typical cellular systems.

When the call is terminated at either end, a brief message is sent over the satellite link between the channel units and noting when the call terminated. The satellite link is then terminated. The caller channel unit then sends a brief message via the signaling returnlinks to the NMS indicating when the call terminated. Therefore the NMS has a complete record of the call and knows which channel units are available at all times. Both channel units then return to an idle state tuned to the outline.

Traffic Topology

Many of the DAMA system can support both Pre-assigned Multiple Access (PAMA) and Demand Assigned Multiple Access (DAMA) voice and Data circuits. All circuits use one satellite hop and can be configured with any combination of Mesh (remote-to-remote) or Star (remote-to-hub) connectivity. DAMA system can be expanded to support more than one satellite or more than one transponders on the same polarization. The DAMA bandwidth pool can be divided into three levels of call priority (high, medium and low). The highest priority is reserved for the most critical channels while the lowest priority is for typical DAMA calls. The extreme flexibility of this system will support any traffic plan.