The earliest LANs used coaxial cables. Over time, the twisted pair cables used in telephone systems were improved to carry higher frequencies and support LAN traffic. More recently, fiber optic cables have emerged as a high-speed cabling option.
Local Area Networks use four types of cables:
•Coaxial
•Unshielded Twisted Pair (UTP)
•Shielded Twisted Pair (STP)
•Fiber Optic
Coaxial Cables
A coaxial cable consists of:
•a single copper conductor
•a layer of shielding with a ground wire
•an outer jacket
Coaxial cables are sometimes used for bus topologies, but many LAN products are dropping support of coaxial cable connectivity.
The Ethernet LAN protocol was originally developed to operate over coaxial cables. 10Base5 / Thicknet cable:
•was the original Ethernet cable.
•is no longer in use in modern LANs. 10Base2 / Thinnet cable:
has a smaller diameter than Thicknet.
•replaced Thicknet.
•is no longer recommended, but is still used in some very small LANs.
Unshielded Twisted Pair
Unshielded twisted pair (UTP) cable is used for both LANs and telephone systems. UTP cables are composed of four color-coded pairs of copper conductors twisted around each other. An outer jacket provides protection and keeps the pairs in alignment. UTP cable connects to devices via 8 pin modular connectors called RJ-45 plugs. All LAN protocols can operate over UTP. Most modern LAN devices are equipped with RJ-45 jacks.
Shielded Twisted Pair
STP cable is also used for Data Networks. It originated with IBM's Token-Ring networks. Its shielding allows greater tolerances for protection from EMI interference, such as from flourescent light fixtures and electric motors.
Fiber Optic Cable
Fiber Optic cables are the latest development in cabling technology. They are constructed from optical glass. There is a central glass filament, called the core, and surrounding layers of cladding, buffer coatings, strengthening materials, and an outer jacket.
Information is transmitted by wavelengths of light. This is accomplished through devices that convert electrical signals into rapid pulses of either LED or Laser light.
Fiber optic cables offer several advantages, including:
•high bandwidth capacity (many gigabits per second).
•longer distances between devices (from 2 to over 60 kilometers).
•immunity to electromagnetic interferences
Fiber optic cables are widely used in WANs for both voice and data communications. The primary barrier to their widespread use in LANs is the cost of electronics.
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