Fiber optic Glass fibers carry modulated pulses of light to represent digital
data signals. Light travels through a fiber optic cable much faster than electrical
impulses through a copper cable, which is why fiber optic cable is used for the
long line portion of WANs and carrying signals between cities.Cable Characteristics
All network cabling has a set of general characteristics that can be used to pick the right
cable for a given networking situation. For a wide majority of networks the cable choice is
UTP,butthereareinstanceswhenUTPmaynotbeappropriate.Herearethecharacteristics
you should consider when making a cable choice: Bandwidth (speed) This is the number of data in bits, typically kilobits
or megabits, a cable can transmit in a second. For example, UTP cable is
nominally rated at 10 Mbps, or ten million bits per second.
Cost This is always a major consideration when choosing a cable type.
Twisted pair cable is the least expensive, but it has limitations that require
other hardware to be installed. Coaxial cable is a little more expensive than
twisted pair; it doesn’t require additional equipment and it is inexpensive to
maintain. Fiber optic cabling is the most expensive, requires skilled installation
labor, and can be difficult to install and maintain.
Maximum segment length When data is transmitted over any cable, there
is a distance at which the transmitted signal begins to weaken and needs to
be reenergized to prevent data errors. This is calledattenuation, and it is the
natural tendency for a signal to weaken as it travels over a cable. This distance
(normally expressed in meters) is the maximum segment length for a cable
medium or the distance at which signals on the cable must be regenerated.
Maximum number of nodes per segments Adding a node to the network
cable reduces its attenuation point, much like punching holes in a water hose
eventually causes no water to reach the end of the hose. Each cable type limits
the number of nodes it can support in a given distance (its maximum segment
length) so it can provide its full bandwidth to all nodes.
Resistance to interference The different cable media resist electromagnetic
interference (EMI) or radio frequency interference (RFI) in varying degrees.
EMI and RFI are caused by electric motors, fluorescent light fixtures, and other
electrically noisy devices located near the network cable. As the construction
of the cable and its cladding (covering) varies, so does its resistance to EMI
and RFI signals.Table 20-2 lists the characteristics of thin and thick coaxial cable, unshielded twisted
pair cable, and fiber optic cable.(^516) PC Hardware: A Beginner’s Guide