B-h Transmission Medium

8/6/2019 B-h Transmission Medium

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Transmission Media


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Transmission Media

Physical Infrastructure components that carry data

from one computer to another .

The physical path that is used to carry a signal

between a signal transmitter and a signal receiver is

called the transmission medium.

There are two types of transmission media:

1. Guided2. Unguided (Wireless)


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Transmission Media

Communication is in the form of electromagnetic

waves.

Characteristics and quality of data transmission are

determined by characteristics of medium and signal.

In guided media, medium characteristics is more

important, whereas in unguided media, signal

characteristics is more important.


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Guided Media

The three most common types of guided

media include twisted-pair cable, coaxial

cable, and fiber optic cable.


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Twisted-pairwiring - a type of cable composed oftwo (or more) copper wires twisted around eachother within a plastic sheath.

The oldest, least expensive, and most commonlyused media.

The wires are twisted to reduce outside electricalinterference.

Up to 250 kHz analog and few Mbps digitalsignaling ( for long-distance point-to-pointsignaling).

Twisted Pair Cable


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Contd

Increasing the number of turns per footreduces the noise interference.

To further improve noise rejection, a foil orwire braid shield is woven around the twistedpairs.

Twisted pairs are of the following kinds:

STP(Shielded Twisted Pair),

UTP(Unshielded Twisted Pair)


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Shielded Twisted Pair (STP)


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Shielded Twisted Pair (STP)

(FTP)


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Unshielded Twisted Pair (UTP)


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Unshielded Twisted Pair (UTP)


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Contd

UTP:most common medium; used in: Telephone network

Between house and local exchange (subscriber loop)

To private branch exchange (PBX)

For local area networks (LAN)

Ethernet at 10Mbps or 100Mbps Advantages :

cheap

easy to work with (to install on walls)

Disadvantages :

susceptible or unresistant to EM interference and noise need for amplification (order of kilometers)

crosstalk


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Coaxial Cable

Coaxial cable - cable that can carry a wide range of frequencies with low

signal loss.

Consists of 2 conductors. The inner conductor is held inside an insulator

with the other conductor woven around it providing a shield. An

insulating protective coating called a jacket covers the outer conductor.

Coaxial Cable


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Contd

Most versatile medium

LANs, Cable TV, Long-distance telephones, VCR to-TVconnections

Noise immunity is good

Very high channel capacity few 100 MHz / few 100 Mbps

Coaxial cable is divided into two different types:

1. Thinnet coaxial cable - similar to the cable used by cabletelevision companies

2. Thicknet coaxial cable - similar to thinnet except that it islarger in diameter


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Optical Fiber

Fiber optic(or "optical fiber") - the technology associated with thetransmission of information as light impulses along a glass or plastic wireor fiber.

The typical optical fibre consists of a very narrow strand of glass calledthe Core. Around the Core is a concentric layer of glass called the

Cladding. A typical Core diameter is6

2.5

microns Typically Cladding has adiameter of 125 microns. Coating the cladding is a protective coatingconsisting of plastic, it is called the Jacket.

Optical Fiber


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Advantages

Extremely high bandwidth: capable of upto2Gbps

Very high noise immunity, resistant to

electromagnetic interference.

Does not radiate energy/cause interference.

Very light in weight.

Very difficult to join Better security


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Light Propagation Modes

Step-index multimode

Graded-index multimode


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Light Propagation Modes

Single mode


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Guided Cable Summary

Media versus BandwidthCable Type Bandwidth

Open Cable 0 - 5 MHz

Twisted Pair 0 - 100 MHz

Coaxial Cable 0 - 600 MHz

Optical Fiber 0 - 2 GHz


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Unguided Media

Unguided media, also called as wireless

communication, transmitting electromagnetic

waves without using a physical conductor.

Examples include microwaves, infrared light

waves, and radio waves


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(Terrestrial) Microwave

Typically used where laying a cable is not Practical.

Parabolic dish shaped antenna ( approx 10 ft diameter)

transmits/receives electromagnetic waves in the 2-40 GHz

range. Travels in a straight line (line-of-sight propagation)

High data rates: 100s Mbps

Repeaters spaced 10 - 100 km apart

Used for Long-distance telephone communication


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(Terrestrial) Microwave


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Satellite Microwave Satellite communication is similar to the terrestrial microwave,

except that the satellite acts as one of the stations.

Source transmits signal to satellite which amplifies or repeats it,

and retransmits down to destinations.

Optimum transmission in 1 - 10 GHz range;

Bandwidth of 100s MHz

Significant propagation delay approx 270 ms

Applications:

Long-distance telephones Television distribution

Private business networks

GPS


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Contd

Satellite Communication


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Contd

VSAT (Very Small Aperture System)

For business data applications requiring high datarates for short periods of time (National WeatherService, news services, credit card verification,automatic tellers, car rental agencies, )

Commonly connects a central location with manyremote ones.

Communication between two sites is via a satellite

and allows a low-cost small antenna dishes( Approx 5 ft)


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VSAT


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(Broadcast) Radio

Electromagnetic wave in the range

30MHz ~1GHz

Omnidirectional i.e. broadcast radio does notrequire dish-shaped antennas.

Less attenuation than microwave.


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Infrared

For short-range communication

Remote controls for TVs, VCRs, and stereos

Indoor wireless LANs

Do not pass through solid walls

Better security and no interference (with asimilar system)

No government license is needed


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TRANSMITTING AND RECEIVING DEVICES the

hardware

Network adapters

Modems

Repeaters

Wiring concentrators, hubs, and switches Bridges, routers, and gateways

Microwave transmitters

Infrared transmitters

Cellular transmitters

Wireless LAN transmitters


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B-h Transmission Medium