Transmission Media Guided Media Guided media, which are those that provide a conduit from one device to another, include twisted- pair cable, coaxial cable, and fiber-optic cable. Topics discussed in this section: Twisted-Pair Cable Coaxial Cable
Twisted-pair Cable• The number of twist per unit length has the effect on the quality of the cable.
How Twisted-Pair Cable Reduces NoiseInterference from devices such as a motor can create unequal noise over two parallel lines.The line that is closer to the device receives more interference than the one that is farther.If however, the wires are twisted around each other at regular intervals, each wire is closer to the noise source for half of the time and farther for the other half.Both receive the same amount of noise. The noise from two wires cancel each other out at the receiver.
UTP and STP cablesUnshielded twisted-pair Shielded twisted-pair
UTP Contd.. Consists of 4 pairs (8 wires) of insulated copper wires typically about 1 mm thick. The wires are twisted together in a helical form. Twisting reduces the interference between pairs of wires. High bandwidth. Flexible and cheap cable.
Categories of UTPUTP comes in several categories that are based on the number of twists in the wires, the diameter of the wires and the material used in the wires.CAT 1,CAT 2,CAT 3, CAT 4, CAT 5, Enhanced CAT 5 ,CAT 6, and now CAT 7.Category 3 is the wiring used primarily for telephone connections.Category 5e and Category 6 are currently the most common Ethernet cables used.
Connecting your Device through UTP Materials Required: *UTP cable: *RJ-45 Connector: (Register jack) *Crimper Tool:
Connecting your Device through UTP T-568A Standard:
ApplicationsTwisted-pair cables are used in telephone lines to provide voice and data channels.The local loop (the line that connects subscribers to the central telephone office) commonly consists of unshielded twisted-pair cables.The DSL(Digital Subscriber Line) lines that are used by the telephone companies to provide high-data-rate connections.High-bandwidth capability of unshielded twisted-pair cables is used in LAN connections.
IBM produced another version of twisted pair cable and that is STP which has a metal foil covering that encases each pair of insulated conductors or wires in pair.
What it is and what it do• STP cable combines the techniques of shielding,cancellation and wire twisting.• Each pair of wires is wrapped in a metallic foil.• The five pairs then wrapped in an overall metallic foil.• STP reduces electrical noise both from a. Within the cable(Pair to pair coupling) b. Outside the cable.
• In addition the metallic shielding must be grounded at both ends of the cable.• If it is improperly grounded the shield acts like an antenna which can pick signals not needed.• It rarely comes in actual use because of its cost and difficult to terminate.
Important points• SPEED – 10 to 100MBPS(1000)• Average cost per node – Expensive than UTP• Media connector size – Medium to large(S-L)• Maximum cable length – 100m
DifferenceWhen comparing UTP and STP we should knowthat:These are the least expensive media for data communication but if we do a comparison of these both then we must know that UTP is less expensive than the STP.
Contd..And because most buildings are already wired with the UTP many transmission standards are adapted to use it to avoid costly rewiring with an alternative cable type like STP.
Few things we should know about STPSTP cable is developed by IBM for token ring that consists of two individual wires wrapped in a foil shielding to help provide a more reliable data connection.
Contd..Token ring-A network where all computers on the network are connected in a circle fashion. The term token is used to describe a segment of information that is sent through that circle; when a computer on the network is able to decode that token, the information is received on that computer.
Contd..• It is a type of wiring in which each of the two wires that are twisted together are coated with an insulating coating.• The extra covering in shielded twisted pair wiring protects the transmission line from electromagnetic interference.
CoaxCoax carries signals of higher frequency ranges (higher Bandwidth) than twisted pair.Inner conductor carries signal.Outer one serves as shield against noise and as the second conductor, which completes the circuit).
Contd…Instead of having two wires, coax has a central core conductor of solid or stranded wire (usually copper) enclosed in an insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid, or a combination of the two.The outer metallic wrapping serves both as a shield against noise and as the second conductor, which completes the circuit.This outer conductor is also enclosed in an insulating sheath, and the whole cable is protected by a plastic cover.
General Rules for CoaxD = diameter of insulation under the shield.d = diameter of inner conductor.Attenuation or LossRaising the D/d ratiolowers attenuation
Categories of CoaxCoax is categorized by Radio Government (RG) rating.Each RG number denotes a unique set of physical spec. (wire gauge of inner conductor, thickness and type of inner insulator, etc.).
Categories:Two kinds: Thicknet (RG-11): It connect 100 devices with range 500m (more expensive ). Thinnet (RG-58): It connect 30 devices within 185 m (cheaper).
BNC connectors To connect coaxial cable to device, we need BNC. Bayone-Neill-Concelman connector is the most common type.• BNC connector is used to connect the end of cable to a device.• BNC T connector is used to branch out the connection.• BNC terminator is used at the end of the cable to prevent reflection of the signal.
Coaxial cable performance**Coax has higher BW but the attenuation is also higher than twisted pair cable.** Requires frequent use of repeaters.
Coaxial Cable ApplicationsMost versatile mediumTelevision distribution Ariel to TV Cable TVLong distance telephone transmission Can carry 10,000 voice calls simultaneously Being replaced by fiber opticShort distance computer systems linksLocal area networks