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
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
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
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
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