Biomedical Engineering Reference
In-Depth Information
Orbiting satellites are special cases of servers connected to workstation clients through long-distance
radio frequency links. The major complicating factor is the need for local uplink and downlink
hardware, including a satellite dish, on the client side. The capabilities of communications satellites
are defined by their orbit—GEO (geostationary earth orbit), MEO (medium earth orbit), or LEO (low
earth orbit)—as well as their operating frequency and bandwidth. The orbit affects the availability and
reliability of communications, the terrestrial antenna requirements, and the latency or lag time
associated with transmit and receive operations.
For example, a GEO satellite provides continental coverage and can be used with a fixed terrestrial
antenna, but has a significant latency because the satellite is orbiting at 36,000 kilometers. In
contrast, a LEO satellite provides only a few Km ground coverage but latency is low because of the
500 to 2000 km orbit. Latency is an issue when data need to be frequently retransmitted because of
errors, which is often the case when the receiver is operating at the fringe of the satellite coverage
area. As a result, a LEO satellite can provide greater throughput than a GEO satellite, all else being
equal.
Network Interface Cards
A Network Interface Card (NIC) is a card or, more often, the part of the workstation motherboard
that provides the client-side connectivity to the network. The NIC is connected to the network
through a variety of media, including coaxial cable, twisted pair, and fiber.
Network Monitors
A network monitor is a specialized device that can monitor or sniff packets and determine throughput
of hardware, as well as detect sources of error, such as a defective network interface card. A network
monitor can also be implemented in the form of a software utility running on a workstation attached
to the network.
Uninterruptible Power Supplies
An Uninterruptible Power Supply (UPS) is a battery and power-filtering device that can provide
emergency power for up to several hours, allowing the hardware to be automatically shut down
without data loss. UPSs, especially those with built-in power conditioners, protect sensitive
equipment and the data they contain from power surges and sudden, unplanned power outages.
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