transmission media

Transmission Media

Presented by:-

Abhishek Wadhwa

Arvind Lal Dass

Nitin Malhotra

Classes of transmission media

Guided Media

Transmission 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 CableCoaxial 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 cables

Unshielded twisted-pair Shielded twisted-pair

Unshielded Twisted Pair (UTP)

Contd..

Consists of 4 pairs (8 wires) of insulatedcopper wires typically about 1 mmthick.

The wires are twisted together in ahelical form.

Twisting reduces the interferencebetween pairs of wires.

High bandwidth.

Flexible and cheap cable.

UTP

Categories of UTP

UTP comes in several categories that are based on thenumber of twists in the wires, the diameter of the wires andthe 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 telephoneconnections.

Category 5e and Category 6 are currently the most commonEthernet cables used.

UTP performance

Connecting your Device through UTP

Materials Required:

*UTP cable:

*RJ-45Connector:(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 isused in LAN connections.

Shielded Twisted Pair (STP)

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 know that:

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 STP

STP 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.

Co-axial Cable

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 Coax

D = diameter of insulation under the shield.

d = diameter of inner conductor.

Attenuation or Loss

Raising the D/d ratio

lowers attenuation

Categories of Coax

Coax 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 connectorsTo 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 Applications

Most versatile medium

Television distribution Ariel to TV Cable TV

Long distance telephone transmissionCan carry 10,000 voice calls simultaneouslyBeing replaced by fiber optic

Short distance computer systems linksLocal area networks

Any

Questions?

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