Biomedical Engineering Reference
In-Depth Information
by the distance from a telephone switching station, and the maximum bandwidth diminishes with
distance from the station. Many academic institutions and some well-funded biotech firms have
access to the Internet through high-bandwidth, secure fiber.
In contrast to the media used for Internet access, the choice of media that can be used to support an
internal LAN is more a function of cost, bandwidth requirements, security, ease of installation, and
type of existing wiring, if any. For example, many older buildings have spare twisted pair cables
running throughout their structure from the telephone service. In some of these buildings, running
cables through asbestos or concrete structures many be prohibitively expensive or time-consuming,
making wireless the only viable media. Another option is to use the power wiring as a data network
medium. However, because the wire isn't twisted but is run parallel, it's more susceptible to noise
than the other common types of media, resulting in a significantly lower maximum bandwidth.
Network Electronics
The media running from office to office and across the country become a useful communications
channel with the addition of electronics capable of sending and receiving signals through the media.
These electronics serve a variety of functions, including:
Generating signals destined for a recipient somewhere in the network
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Coordinating signals through media in order to minimize interference
Amplifying and conditioning signals so that they can continue error-free to their destination
Blocking signals from certain paths to minimize interference in those paths
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Routing signals down the quickest or least-expensive route from source to destination
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Translating signals originally designed to work with one protocol so that they are compatible
with networks designed to support other protocols
Connecting different networks
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Monitoring the status of the network, including the functioning of network electronics and the
amount of data on segments of the network
Although there are hundreds of devices on the market that transmit, receive, manage, convert,
block, redirect, and monitor signals on the network, most fit into the categories listed in
Table 3-3
.
Several of the network devices listed in
Table 3-3
are illustrated in context in
Figure 3-11
on page
130. However, it's important to note that the physical layout of the network depicted in this figure
may have little relation to the logical functioning of the network electronics. For example, even
though the workstations or clients are connected directly to the printer, all printing requests or jobs
may be directed to the print server, which manages the printing queue and buffers printing requests,
freeing the processors in the workstation clients to handle other computations instead of devoting
machine cycles to managing individual print jobs.
Figure 3-11. Network Hardware. The physical architecture shown here may
support a markedly different logical architecture.
