[Top] | [Previous] | [Next]

5.3 Network Topology

A notional network topology is shown in Figure 15. The LAN configuration is based on a dual-hubbed approach for reliability. Network management software will automatically reroute network traffic through the alternate hub in case of failure. In addition, file sharing software (e.g., the Network File System (NFS)) permits running any application on any workstation and accessing data from any disk.

Figure 15. Notional network topology.

The ability to run any application on any platform assumes the computer has sufficient power to perform the task. For this reason, certain computers on the diagram are labeled as planning workstations, display workstations, database server, contact server, and FEP. Planning workstations are intended to perform functions such as orbit determination, attitude determination, and mission planning. In addition, they may be used for "back-room" telemetry analysis. Some are connected directly to LAN hubs for speed and reliability, but some could be connected to FDDI or ethernet subLANs for analysis and network system administration. Benchmarks have indicated that a high-end, desktop workstation such as a Sun Sparc20 should suffice for any single planning function. Therefore, to handle the total load, several such workstations will be required to allow for peak workloads and provide redundant computer resources.

The remaining computers in Figure 15 are included to handle the real-time and possible high-rate telemetry and commanding functions. These include servers designed to handle the high-speed computing needed for high-rate telemetry and complex commanding functions. The servers are coupled with FEPs which share the load and process data coming in through a series of encryption/decryption and other interface boxes. Certain FEPs, particularly those employed for lower data rates, can handle more than one simultaneous contact; multiple strings of these interface boxes are indicated. In addition, multiple display workstations could be included with each FEP-server combination.

The final server type is the database/file server. The function of this computer is to service clients such as Orbit or Attitude who need processed telemetry data (possibly during a contact) in order to separate the processing load and avoid spikes in this load that could bog down a contact server or display workstation. These servers can be sparsely distributed on the network since typical loads are not expected to stress this server.

Disk storage is distributed randomly on the network to support swap space, temporary data storage, and permanent storage of executables. Because of file sharing software, the physical location of disk storage is not an architecture driver, except for telemetry archiving, where the network bandwidth may be a limiting factor at higher data rates and a central archiving server is desired to facilitate storage management.