Cable is the actual physical path upon which
an electrical signal travels as it moves from one component
Transmission protocols determine how NIC cards take turns
transmitting data onto the cable. Remember that we discussed
how LAN cables (baseband) carry one signal, while WAN cables
(broadband) carry multiple signals. There are three primary
- Twisted-pair (or copper)
- Coaxial cable and
- Fiber-optic cable
Twisted-pair (or copper)
Unshielded twisted-pair (UTP) is a four-pair
wire medium used in a variety of networks. UTP does not require
the fixed spacing between connections that is necessary with
coaxial-type connections. There are five types of UTP cabling
commonly used as shown below:
- Category 1: Used for telephone communications.
It is not suitable for transmitting data.
- Category 2: Capable of transmitting data at speeds
up to 4 Mbps.
- Category 3: Used in 10BaseT networks and can
transmit data at speeds up to 10 Mbps.
- Category 4: Used in Token Ring networks. Can
transmit data at speeds up to 16 Mbps.
- Category 5: Can transmit data at speeds up to
Shielded twisted-pair (STP) is a two-pair wiring medium used
in a variety of network implementations. STP cabling has a
layer of shielded insulation to reduce EMI. Token Ring runs
Using UTP and STP:
- Speed is usually satisfactory for local-area
- These are the least expensive media for data
communication. UTP is cheaper than STP.
- Because most buildings are already wired with
UTP, many transmission standards are adapted to use
it to avoid costly re-wiring of an alternative cable type.
Coaxial cable consists of a solid copper
core surrounded by an insulator, a combination shield and
ground wire, and an outer protective jacket.
The shielding on coaxial cable makes it less susceptible to
interference from outside sources. It requires termination
at each end of the cable, as well as a single ground connection.
Coax supports 10/100 Mbps and is relatively inexpensive, although
more costly than UTP.
Coaxial can be cabled over longer distances than twisted-pair
cable. For example, Ethernet can run at speed over approximately
100 m (300 feet) of twisted pair. Using coaxial cable increases
this distance to 500 m.
Fiber-optic cable consists of glass fiber
surrounded by shielding protection: a plastic shield, kevlar
reinforcing, and an outer jacket. Fiber-optic cable is the
most expensive of the three types discussed in this section,
but it supports 100+ Mbps line speeds.
There are two types of fiber cable:
- Single or mono-mode—Allows only one mode
(or wavelength) of light to propagate through the fiber;
is capable of higher bandwidth and greater distances than
multimode. Often used for campus backbones.
Uses lasers as the light generating method. Single mode is
much more expensive than multimode cable.
Maximum cable length is 100 km.
- Multimode—Allows multiple modes of light
to propagate through the fiber. Often used for workgroup
applications. Uses light-emitting diodes (LEDs) as light generating
device. Maximum cable length is 2 km.