Introduction to

Data Communication

DCS201- Computer Science

By:Dilum Bandara

Outline

n Terminologyn Transmission medium

n Guided median Unguided media

Data Communication

n Is the process of transmitting data from one computer to another

n Focus is on the transmission medium, different signal levels & data coding

Terminology

n Bit raten Number of bits per secondn Given in bps

n Baud raten Number of signal variations per secondn Given in bauds per sec

n Bandwidthn Maximum frequency supported by the medium

Transmission Medium

n Provides the path for data communication

n Allows a bit stream to be transported from one machine to another

n Can be categorised as n Guided median Unguided media

Guided media

n Copper wiresn Twisted Pair

n UTP – Unshielded Twisted Pairn STP - Shielded Twisted Pair

n Coaxial cables

n Fibre

Unguided media

n Radio wavesn Microwave linksn IR – Infra Red

Twisted pair

n Pairs of insulated copper wires twisted together n for the reduction of Electro Magnetic

Interference

n Covered with an outer insulating jacketn Two types

n Shielded twisted-pair (STP)n Unshielded twisted-pair (UTP)

Twisted pair cont…

n One or more pairs of wiren Twisted around one anothern Resistant to interferencen A parallel set of wires forms an antenna

but twisted pair does not n Limits signals influence on other pair

n Referred as Crosstalk

STP & UTP

UTP

n UTP cables are grouped in several categorisesn Category 1 – Voicegrade telephone cablingn Category 2 – up to 4 Mbps 4 pairsn Category 3 – up to 10 Mbps 4 pairsn Category 4 – up to 16 Mbps 4 pairs n Category 5 – up to 100 Mbps 4 pairsn Category 5e – up to 1 Gbps 4 pairs

Pros & Cons

n Inexpensiven Easy to work withn Can run up to several Kilometres

without amplification n For long distances repeaters are needed

n With the distance bandwidth reduces n High number of twists per meter

reduces the crosstalk

Coaxial cablesn In early days of networking these types

of cables were heavily used

Types of cables

n 50 O - Baseband Coaxial Cablen Used in digital transmission

n 75 O - Broadband Coaxial Cablen Used for analog transmission n Used for TV antennas & Cable TV

Advantages of Coaxial cables

n Easy to installn Inexpensiven Since it is shielded can span a higher

distance at higher speed than twisted pair

n High bandwidthn Excellent noise immunity

Disadvantages of Coaxial cables

n Higher cost compared to twisted pairn Harder to work with & cable easily get

damaged

Fibre optics

n Bundle of glass or plastic fibresn Sends signals on pulses of light

n Based on the concept of Total Internal Reflection

n Immune to Electro Magnetic & other interferences

n High bandwidth, speed, long distance

Fibre optics cont…

Components of a fibre system

n Light sourcen Transmission mediumn Light detector

Light sourceLight detector

Components of a fibre system cont…

n Light Sourcen Converts electrical signals to optical signals

n Transmission Mediumn Transmits the light signal from one point to

anothern Detector

n Detects the light signal & converts it back to electrical signals

Types of fibre

n Single Mode fibren Harder to manufactory so high costn High speedn Long distance (up to 100Km)

n Multi Mode fibren Low costn Low speedn Lower distance (2 Km)

Types of fibre cont…

Single Mode fibre

Multi Mode fibre

Jacket (Plastic)

Cladding (Glass)

Core (Glass)

Radio Transmission

n Unguided transmission - Intangible median Easy to generaten Travel long distancesn Penetrate buildings easilyn Omni directionaln At high frequencies they travel in straight linesn Absorbed by rainn Reflected by ionosphere

Wireless Networkingn Use is increasing with the introduction

of mobile devicesn Cost is decreasingn Hybrid networks use cable & wireless

Wireless LAN Technologies

n Infrared (IR)n Laser or light waven Microwave Transmissionn Satellite Communications

Infrared (IR)n Uses IR signals transmit datan Used for short range communicationn Do not pass through solid objectsn Simple to develop & cost effectiven Low speedn Cannot be used outdoorn Used in remote controllers, hand held

devices, laptops, etc.

Light wave Transmission

n Can be used to interconnect LANs in 2 different buildings

n Highly focused & coherentn Requires very high degree of alignment

between transmitter & detectorn Cannot penetrate rain or thick fog

Microwave Transmission

n Above 100MHz, waves travel in straight linesn Can be narrowly focusedn Can be concentrated to a small beam using

parabolic antennaen Antennas at transmitter & receiver must be

aligned (Line of Sight)n Long distance links must have repeatersn Does not penetrate through objects

Satellite Communication

n Make use of geosynchronous Satellitesn Orbiting the earth at a distance of 36000

km above the equator

n Period of the satellite is 24 hoursn Uses different bands for different

purposesn Telecommunication, TV braodcasting

UTP Cat 5e Cables

n Used with 10/100/1000 Ethernetn Most heavily used cabling typesn Are connected to networking devices

through RJ45 Jacks

RJ45 cabling

n Has 8 wiresn But only 4 are used

n 2 for transmitting datan 2 for receiving data

Types of RJ45 cabling

n Straight Cablesn Cross Cablesn Rollover cables

Straight Cable

Cross Cable

Wire pairs