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<sect1 id="Media-Types">
Common network media include twisted pair (UTP and STP), coaxial cable,
fiber-optic cable, and wireless transmissions via infrared and radio waves.
Network media are usually chosen based on several criteria: their cost,
their vulnerability to EMI and eavesdropping, their bandwidth, and the
maximum distance at which they can be used.
<varlistentry><term>Twisted Pair Ethernet Cable</term>
<varlistentry><term>Unshielded Twisted Pair (UTP)</term>
UTP is the most common type of network cable in use today. UTP consits of
one or more pairs of insulated copper wires. The wires are twisted together
to reduce crosstalk, and enclosed in a plastic insulator. UTP is the type of
cable used in telephone systems.
UTP cables are generally wires using RJ-45 jacks and plugs. These are
8-conductor connectors similar to the RJ-11 connectors used in telephone
cables. UTP is inexpensive and easy to install compared with other types of
cable, although the differenet types of UTP vary in cost.
Copper wire has a high level of attenuation. YTP cable is limited to
transmission distances of 100 meters or less. UTP is more susceptible
to interference (EMI) than mos types of cable, and is vaulnerable to
eavesdropping since its own emissions are not shielded.
Types of UTP cable are defined by the EIA standards, which specify the three
categories of cable. Category 3 is the minimum requiredment for networking,
and Category 5 is the highest-quality network cable. The UTP categories and
the bandwidth they support are summarized below.
Category Maximum Data and Transfer Rate Description
3 10 Mbps Least expensive network cable
4 16 Mbps Medium quality; rarely used
5 100 Mbps Highest quality; highly prevelant
> Start Binh
5 1000Mbps Highest Quality
> End Binh
<varlistentry><term>Shielded Twisted Pair (STP)</term>
STP cable is similar to UTP, but inclues a foil or wire mesh shield
between the wire pairs and the outer insulation. The shield is electrically
grounded, and reduces emissions and susceptibility to EMI. STP cable is used
in some Token Ting and AppleTalk networks. STP is more expensive than
UTP, and its thickness and rigidity make it more difficult to install. It
also uses grounded connection connectors, adding to the expense. STP uses
the same copper wires as UTP as the same level of attenuation, and therefore
the same maximum distance of about 100 meters. However, it is much less
susceptible to EMI and eavesdropping. The reduced inteference allows for higher
bandwidth, potentially as high as 500 Mbps.
Coaxial Cable consists of a single thick copper wire surrounded by an
insulator. A shield surrounding the insulator is used as the second conductor,
and is encased in an outer insulation. One type of coaxial cable is that used
for cable television. The shielding cable makes coaxial cable less susceptible
to EMI and emissions than UTP. The cable used in most nteworks is either
Thick Ethernet (RG-8) or Thin Ethernet (RG-58). Thin coaxial cable is less
expensive than the highest quality (Category 5) UTP, but is more difficult to
install due to its thickness, its lack of flexibility, the connectors (you
should keep the length of cable between the `T piece' and the actual ethernet
card in the PC as short as possible, ideally the `T piece' will be plugged
directly into the ethernet card), and the neccesity for terminators (a
terminator is a 52 ohm resistor that helps to ensure that the signal is
absorbed and not reflected when it reaches the end of the cable. Without a
terminator at each end of the cabling you may find that the ethernet is
unreliable or doesn't work at all).
The most commonly available types of coaxial cable are described in the table
Type Impendance Common Cable
RG-8 50 ohms Thick Ethernet (thicknet)
RG-11 50 ohms Thick Ethernet (thicknet)
RG-58 50 ohms Thin Ethernet (thinnet)
RG-59 75 ohms Cable TV
RG-62 93 ohms ARCnet
<varlistentry><term>Fiber Optic</term>
A fiber optic cable consists of a thin glass or clear plastic fiber encased
in a protective jacket. Signals are sent through the cable in form of light.
There are two types of fiber optic cable: single-mode, which uses a single
wavelength, and multimode, which uses multiple wavelengths in the
same cable. Fiber optic cable is completely invulnerable to EMI, and has no
detectable emissions. However, it and its associated equipment are expensive
compared to other types of cable, and the most difficult to install. Single-mode
cable is much more expensive than multimode cable. The advantages of fiber are
high bandwidth (up to 2 Gbps (gigabits per second) and extremely low attenuation.
Fiber cable can reach distances ranging from several miles for multimode cable
to hundreds of miles for single-mode cable.
Wireless infrared networking systems are modulated beams of infrared light to
transmit data. These types of networks require a line of sight, and are
generally used for short distances such as networks within buildings or between
nearby buildings. Infrared communications are not subject to EMI, but are
vulnerable to obstructions (such as weather conditions) and bright light, and
suseceptible to eavesdropping. There are two types of infrared networks:
- Point-to-point networks use a focused beam, usually generated by a laser.
They are less vulnerable to dispersion and can theorectically be used for long
distance networking, although the need for precise alignment between receiever
and transmitter and the vulneraibility to obstructions often makes it
impractical. Bandwidth can be as high as 16 Mbps.
- Broadcast networks use a less focused beam that disperses rapidly. These
systems can transmit to multiple workstations ar once, but are much more
vulnerable to dispersion, limiting their useful distance and bandwidth.
Bandwidth is usually no more than 1 Mbps.
Even though wireless technology has only been around for a few years adoption
of this technlogy has been quite successful due to the convenience of the
technology, the relatively low cast and the increasingly better security
that is available within the technology. Wireless technology may also
sometimes be referred to as 'Wifi' (Wireless Fidelity) or 802.11/b/g/n
which refers to the subsequent generations in the technology which have
resulted in better efficiency, faster speed (802.11b runs at 11mbps while 802.11g
runs at 54mbps and 802.11g runs at 110mbps), as well as increased security.
The most common type of wireless networks use radio waves. Tdaio-based networks
have a reasonably high bandwidth, but are very sensitve to EMI and eavesdropping.
Also, many radio frequencies are regulated by the FCC and are unavailable for use
without a license. There are three types of radio links:
- Low power single frequency
This type of system is best suited for small ares, such as within a building. It
uses a lower-power transmitter on a single radio frequency. The available range is
approximately 30 meters. This is the lowest-cost method of radio networking.
Bandwidth may be as high as 10 Mbps.
- High power single frequency
This system is also uses a single frequency, but at a higher power. This allows
for a much greater range, often covering an entire metropolitan area. Bandwidth is
typically 10 Mbps. The greater range makes this type of network the most vulnerable
to eavesdropping.
- Spread-spectrum
These systems use multiple frequencies, primarily to avoid eavesdropping. This
is done in two ways, direct sequence modulation sends packets sequentially over
several different frequencies, while frequency hopping transmission change
frequencies at scheduled intervals known to both ends. Both of these are
significantly less vulnerable less vulnerable to EMI and snooping than other
radio networks.
Another type of wireless network communications uses microwaves, which are
similar to radio waves but at a higher frequency. Higher frequencies are less
vulnerable to interference and snooping, and can provide greater bandwidth.
Two common types of microwave networks are in use:
- Terrestial
This method provides for line-of-sight communication, usually across a short
distance. Bandwidth can be as high as 10 Mbps. Microwaves are still vulnerable
to interference and eavesropping, although not as much as conventional radio
- Satellite
This method relays microwave transmissions via a satellite, allowing for a
nearly global range. The bandwidth can be as high as 10 Mbps, but the satellite
relays cause delays that may impair real-time communication. These systems are
more expensive than wireless communication.
Please note that any information after this point in this section is largely
redundant as these technologies have been superceded (from the perspective of
being economically more viable and also technologically superior) by
those that have been outlined above.
- Serial NULL Modem cable
- Parallel port cable (PLIP cable)