Networks - Bioinformatics Computing - page 104

Fiber. As summarized in Figure 3-10 , of the most popular media used in networks, glass fiber
provides the greatest bandwidth, highest level of security, greatest range, and resistance to electrical
noise. Although fiber provides a working range of up to several kilometers with standard electronics,
it's less flexible to install compared to copper cable. For example, unlike twisted pair or coaxial cable,
fiber can't be snaked through very tight turns because the glass fiber is more fragile than the copper
or aluminum wire used in the coaxial cable, twisted pair, or power line cable.
From a security perspective, fiber is the superior medium because, unlike the other copper cables or
wireless, there is no radio frequency signal that can be intercepted by a nearby receiver. A wire run
in parallel with a twisted pair or coaxial cable acts as an antenna to pick up the signals traversing
through the cable that can be amplified and interpreted. In contrast, the light in a fiber cable is
confined to the optical fiber, which is additionally shielded by a tough sheath. Furthermore, whereas
coaxial cable or twisted pair can be tapped without detection, tapping into a fiber strand results in a
marked, detectable drop in signal level because of the loss associated with a physical tap.
Twisted Pair. Twisted pair cable, the wiring used in virtually every office and residence for
telephone communications, is a comprise between cost, bandwidth, security, and availability. It's
more affordable than coaxial cable or fiber, but the bandwidth isn't as great, and security is a much
greater concern. When used with radio frequency network signals, twisted pair cables don't perfectly
cancel out the signals traversing the two wires, but act as antennas. As a result, not only are signals
in the cable more readily intercepted, but the twisted pair cable is more susceptible to electrical noise
in the environment. For this reason, twisted pair may not be able to be used in laboratory settings in
which electronic equipment may interfere with the network signals, or in which the radiated network
signals may interfere with sensitive laboratory equipment. One option is to use shielded twisted pair
cable, but this usually involves running the special cable in walls because standard telephone twisted
pair cable is unshielded.
Power Line Cable. Power line cable is a low-cost, low-bandwidth solution to networking. Although it
may be suitable for exchanging text-only e-mails and other small files, the limitations of the medium
prevent it from being a serious network medium for bioinformatics applications. It may be a viable as
part of a redundant backup network system, however.
Ether. As a conduit for light or radio frequency signals, the ether provides the greatest flexibility of
the options listed here, but also presents the greatest security risk. Typical internal installations for
wireless LANs are limited to the same floor in a building. However, within that space, users may have
complete mobility with laptops or desktop workstations that are frequently moved. Optical LANs,
based on infrared (IR) links are line-of-sight only, and are limited to a single work area.
Radio frequency communications are also commonly used between buildings, in the form of
microwave links. These links tend to be line-of-sight and limited to perhaps 30 miles, depending on
terrain and buildings that may interfere with line-of-sight communications. Unlike the radio frequency
technology used with LANs, the bandwidth of these links is on the same order as coaxial cable.
Similarly, radio frequency satellite links that extend thousands of miles support high-bandwidth
transmission rates comparable to that provided by coaxial cable and fiber media.
Note that the media characteristics summarized in Figure 3-10 reflect the physical properties of the
media as well as the current state of the art in network electronics. For example, although wireless
LANs are limited to a range of about 200 meters because of legal restrictions on the power of the
electronics, the ether is capable of supporting communications across virtually infinite distances, and
satellite-based wireless Internet connectivity is a viable alternative to wire, fiber, and cable in remote
areas. Similarly, although glass fiber is less expensive than coaxial cable, the associated electronics
and connectors are more expensive and more difficult to use.
The type of media used for Internet access depends primarily on the types of service available, and
secondarily on the bandwidth, security, and cost constraints. For example, the TV cable companies
that offer Internet service use coaxial cable to feed cable modems. Conversely, DSL companies
provide access to the Internet through the same type of twisted pair used by the telephone
companies. Because of the losses associated with ordinary twisted pair cable, DSL service is limited