TRASMISSION MEDIA

TRASMISSION MEDIA

TRANSMISSION MEDIAIt is a pathway that carries the information from sender to receiver.Different types of cables or waves are used to transmit data.Data is transmitted through:-

ELECTRICAL SIGNAL-It is in the form of current.ELECTROMAGNETIC SIGNAL-It is is eries of electromagnetic energy pulses at various frequencies.

TRANSMISSION CAPABILITIESTRANSMISSION CAPABILITIES depends uponBANDWIDTH -data carrying capacity of medium or channel. higher bandwidth, higher data ratesRADIATION -leakage of signal from the medium due to undesirable characteristics of the medium.NOISE ABSORPTION -the susceptibility of the media to external electrical noise that can cause distortion of data signal.ATTENUATION -loss of energy as signal propagates outward. The amount of energy lost depends on frequency.

TYPES OF TRANSMISSION MEDIATYPES

MAGNETIC MEDIAIt is one of the way to transport data from one computer to another by writing it on magnetic tape or removable media and physically transporting the tape to the destination machine and read them again.Example:DVD has capacity in tera bytes.Advantages:It is more cost effective, for application in which high bandwidth or cost per bit transported is the key feature.

OPTICAL FIBREIt consists of THIN GLASS FIBRES or plastic that can carry information at frequencies in the visible light spectrum and beyond.The typical optical fiber consists of a very narrow strand of glass called the core(62.5 microns). Around the core is a concentric layer of glass called CLADDING(125microns). coating of cladding is protective consists of plastic(jacket).

OPTICAL FIBRE COMPONENTS

REFRACTIONLight ray passes from one medium to another, the ray is refracted at the boundary at an angle 1 and emerging at an angle 1.The amount of refraction depends upon the properties of two medium.For an angle of incidence above a critical value, the light is refracted back into the medium. None of its escapes into the air.

TYPES OF OPTICAL FIBRES

TYPES OF FIBERSSINGLE MODE FIBRE:Diameter::8 to 10 micronsLight can propagate only in straight line without bouncing.Critical angle close enough to 90 degree such that beam propagates in a straight line.These are expensive and are widely used for long distance communication.Can transmit data at 50 gbps for 100 kilometers without amplification.MULTIMODE FIBRE:Multiple beams travel in the core in different paths.Diameter:50 microns

MULTIMODE FIBRESTEP INDEX FIBRE:Density of core remains constant from the centre to the edges.A beam of light moves in a straight line in this medium until it reaches the interface of core and cladding.At this intterface,the angle of ray is changed due to the change in density.In this mode,some beams travel in the straight line through the core and reaches destination without reflection or refraction.The beams that strike the interface of core and cladding at and angle smaller than critical angle penetrate the cladding and are lost.The beams striking at angle greater than critical angle are reflected back in core and forms total internal reflection.GRADED INDEX FIBREIt has different densities at the core and at the edge.Because of this difference in densities different beams refract at different angles into a curve.Only the horizontal beams move in a straight line due to constant density at the center

ADVANTAGES OF OPTICAL FIBRESNot affected by electrical and magnetic interference as the data travel in for of light.higher bandwidthThin, lighter , small in sizeCan easily be grouped in one bundle.Glass can be laid in different environments.Attenuation is very low. Attenuation =10 log 10 transmitted power/receieved power. It is measured in decibels.Provide Security against wire tappers as they do not leak lightNo cross-talk problem.Lower cost as material used in them silica glass is easily available.Information carrying capacity is much higher.Transmission rate:45 mb/s to 9.6 gb/s

DISADVANTAGES OF OPTICAL FIBERFragileMore easily broken than wires.Need to be put deep into land. Causes lot of installation cost.Being new in technology require skilled people for administration and maintenance Optical fibers are unidirectional for two way communication, two fibers are required.

APPLICATION OF OPTICAL FIBERIn the local area networks.In telephone lines.In backbone of networks.

CO-AXIAL CABLESKnown as COAXTwo kinds of co-axial cables are used.50 ohm75 ohm Used for analog transmission and cable televisionIt can span longer distance.

TYPESBASEBAND -transmit a signal at a time at very high speed-supports frequency range of 4kHz-cables are 50 ohms-can be used with low data rates or periodic amplifiersBROADBAND -transmit many simultaneous signals using different frequencies-supports frequency range above 4kHz-cables are 75 ohms-can be used for analog transmission.

STRUCTURE OF COAXIAL CABLEIt consists of a stiff copper wire as the core,surronded by an insulating material.This insulator is encased in a conductor, often as a closely woven braided mesh.the outer conductor is covered in a protective plastic sheath.

ADVANTAGES/DISADVANTAGESADVANTAGES:Can be used for both analog and digital transmissionOofer high bandwidthLoss of signal or attenuation is less due to better shieldingAlso offers good noise immunityInexpensive as compared to optical fiberLower error rates compared to twisted pairNot easy to tap because copper wire is contained in plastic jacketDISADVANTAGES:High installation costHigh maintenance cost

APPLICATIONS OF COAXIAL CABLESAnalog telephone networsDigital telephone networksCable tvTraditional ethernet lansDigital transmissionThick ethernet

TWISTED PAIRSTwisted pair consists of two copper wires about 1mm thick.These wires are twisted together in helical form.Polyethylene, polyvinyl chloride, four polymer resin and Teflon(r) some of the substances that are used for insulation purposes.Gauge: it is measure of thickness of the conductor. The thicker the wire the less is the resistance, the stronger the signal over a given distance and the better the performance of the medium.The bandwidth of twisted pair depends on-The gauge of the conductorLength of the conductorSpacing of the amplifiers

WHY TWISTING?Number of twists per unit length will determine the quality of cable. More twists means better quality.Twisting of wires will reduce the effect of noise or external interference.If the two wires are parallel the the electromagnetic interference from the devices such as motor can a create a noise .Interference on the wire that is closer to the source of the noise this results in high voltage level in one wire than the other.this further leads to uneven load and damaged signal and there will difference at the receiver side.If the two wires are twisted ,then the comulative effect of the interference on both the wires are equal.in one twist one wire is closer to the noise source and the other is farther,in the next twist the reverse is true In this way , there will be no difference at the reciever side as unwanted signals are cancelled out.

STP-SHIELDED TWISTED PAIRS-made up of copper wires that are twisted together.-the pairs are covered in a foil or braided mesh, as well as outer PVC jacket.This foil or mesh prevents the penetration of em noise and eliminate cross talk-this shielding must be grounded to prevent the foil or braided mesh from becomin a magent for electricity.TYPES OF TWISTED PAIRSUTP -UNSHIELDE TWISTED PAIR-Consists of color-coded copper wires, but does not include any foil or braiding-wire pairs within each cable have varied amounts of twists per foot to produce cancellation.-there are several categories of UTP.

ADVANTAGES OF STP OVER UTP:STP is less susceptible to noise as compared to UTP and therefore reduces the cross talk and interferenceDISADVANTAGES OF STP:It must be properly grounded. It is more expensive than UTP.It is difficult to terminate

ADVANTAGES OF TWISTED PAIRSIt can be used to carry both analog and digital data.It is relatively easy to implement and terminate.It is the least expensive media of transmission for short distancesIf portion of a twisted pair cable is damaged it does not effect the entire network.

DISADVANTAGES OF TWISTED PAIRSIt offers poor noise immunity as a result signal distortion is moroe.Attenuation is very high.It supports lower bandwidth as compared to other medias.It supports 10 mbps upto a distance of 100 meters.It offers poor security and are easily to tap.Being thin in size they are likely to break easily.

APLICATION OF TWISTED PAIRSIn telephone lines to carry voice and data channels.In the local loopIn the DSL(ADSL) in Local area networkIn the ISDN

WIRELESS TRANSMISSIONFor the users who use mobile,laptops,notebook,palmtop,wrist-watch computers coax fibers are of no useSo, wireless network is introduced

RADIO TRANSMISSIONRadio waves are easy to generate,can travel long distances,and can penetrate buildings easilyThey are widely used for communication,both indoors and outdoors.Radio waves are omnidirectionalThey travel in all directions from the source.

RADIO-WAVESThey are frequency dependentAT LOW FREQUENCY: radio waves pass through obstacles well the power falls off sharply with distance from the source, roughly as 1/r(square) in airIn VLF,LF and MF bands ,radio waves follows ground, asPROBLEM:These bands has low bandwidthThese waves can be detected for thousand kilometers at the lower frequencies less at the higher onesFor example: AM radio broadcasting

AT HIGHER FREQUENCYRadio waves tend to travel in straight lines and bounce off obstacles.They are also absorbed by the rain.At all frequencies,radio waves are subject to interference from motors and other electricalequipments. How ever the waves that reach the ionosphere are refracted by it and send back to the earthThe military also communicates HF and VHF bands

MICROWAVE TRANSMISSIONThe microwave travels in a straight line if the towers are too far apartThe earth will get in the way so repeaters are required periodically.The higher the towers are the farther apart they can be.For 100meter high tower repeaters can be spaced 80 km apart.Microwave do not pass through buildings.Some waves may be refracted of low line atmospheric layers and may take slightly longer to arrive out of phase with direct wave and thus cancel the signalThis effect is called multipath fadingMicrowave communication is so widely used for long distance, telephone communication, mobile phones, television.They are relatively inexpensive.

INFRARED RANGE They are widely used for short range communicationUses:Remote control on television,vcr,steriosADVANTAGES: They are relativelyDirectionalCheapEasy to builtLimitation:They do not pass through solid objects.

LIGHT WAVE TRANSMISSIONThe laser's strength has very narrow beamIt can penetrate rain or thick fog.It is also responsible for shimmering roads on a hot day and wavy images seen when one looks out above a hot radiator.

REFERENCE +2 text book(PSEB) COMPUTER NETWORKS(Andrew S.Tanenbaum) PEARSON(4th edition)www.ecomputernotes.com/computernetworkingnotes/communication-networks/describe-the-different-transmisssion-media