1. BY KINISH KUMAR(www.kinishcybersec.blogspot.in)http://www.facebook.com/kinishkumar

2. Transmission media Transmission mediaare located below thephysical layer Computers use signalsto represent data. Signals are ransmittedin form ofelectromagneticenergy. 3. Transmission MediaTransmission Media and Physical Layer 4. Transmission Media Guided Media (Wired) Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable Unguided Media (Wireless) Radio Waves Microwaves Infrared 5. Classes of transmission media 6. GUIDED MEDIAGuided media, which are those that provide a conduitfrom one device to another, include twisted-pair cable,coaxial cable, and fiber-optic cable. 7. Overview The transmission media that are used to convey information can beclassified as guided or unguided. Guided media provide a physicalpath along which the signals are propagated; these include twistedpair, coaxial cable, and optical fiber. Unguided media employ anantenna for transmitting through air, vacuum, or water. The characteristics and quality of a data transmission are determinedboth by the characteristics of the medium and the characteristics ofthe signal. In the case of guided media, the medium itself is moreimportant in determining the limitations of transmission. For unguided media, the bandwidth of the signal produced by thetransmitting antenna is more important than the medium indetermining transmission characteristics. One key property of signalstransmitted by antenna is directionality. In general, signals at lowerfrequencies are omnidirectional; that is, the signal propagates in alldirections from the antenna. At higher frequencies, it is possible tofocus the signal into a directional beam. In considering the design ofdata transmission systems, key concerns are data rate and distance:the greater the data rate and distance the better. 8. Data Rate and Bandwidth Any transmission system has a limited band offrequencies This limits the data rate that can be carried 9. Design Factors Bandwidth higher bandwidth gives higher data rate Transmission impairments eg. attenuation Interference Number of receivers in guided media more receivers introduces more attenuation 10. Guided Media Twisted-pair Cable Twisted-pair cable 11. Twisted Pair 12. Twisted pair One of the wires carries signal, the other is used only as a groundreference. The receiver uses the difference b/w the two levels. Twisting increases the probability that both wires are effected bythe noise in the same manner, thus the difference at the receiverremains same. Therefore, number of twists per unit length determines thequality of the cable. 13. Twisted Pair - TransmissionCharacteristics analog needs amplifiers every 5km to 6km digital can use either analog or digital signals needs a repeater every 2-3km limited distance limited bandwidth (1MHz) limited data rate (100MHz) susceptible to interference and noise 14. Unshielded Versus Shielded Twisted-Pair Cable UTP and STP cables 15. Unshielded Twisted Pair (UTP) Ordinary telephonewire Cheapest Easiest to install Suffers from externalEM interference 16. Shielded Twisted Pair (STP) Metal braid orsheathing that reducesinterference More expensive Harder to handle(thick, heavy) 17. Near End Crosstalk coupling of signal from one pair to another occurs when transmit signal entering the link couplesback to receiving pair ie. near transmitted signal is picked up by nearreceiving pair 18. Categories of unshielded twisted-pair cables 19. UTP Categories 20. Guided Media UTPUTP Connector 21. Guided Media - UTP Applications: Telephone lines connecting subscribers to the central office DSL lines LAN 10Base-T and 100Base-T 22. Twisted Pair - Applications Most common medium Telephone network Within buildings For local area networks (LAN) 23. Twisted Pair - Pros and Cons Cheap Easy to work with Low data rate Short range 24. Guided Media Coaxial CableCoaxial Cable 25. Coaxial Cable 26. Coaxial cable Inner conductor is asolid wire outerconductor serves bothas a shield against noise and asecond conductor 27. Coaxial Cable Applications Most versatile medium Television distribution Long distance telephone transmission Can carry 10,000 voice calls simultaneously Short distance computer systems links Local area networks 28. Coaxial Cable - TransmissionCharacteristics superior frequency characteristics to TP performance limited by attenuation & noise analog signals amplifiers every few km closer if higher frequency up to 500MHz digital signals repeater every 1km closer for higher data rates 29. Guided Media Coaxial CableCategories of coaxial cables 30. Guided Media Coaxial CableBNC Connectors 31. BNC connectors BNC = Bayone-Neill-Concelman BNC Connector is used toconnect the end of thecable to a device BNC T is used in networksto branch out a cable forconnection to a computeror other device BNC Terminator is used atthe end of the cable toprevent the reflection ofsignal. 32. Coaxial cable performance 33. Guided Media Coaxial Cable Applications: Analog telephone networks Cable TV networks Traditional Ethernet LAN 10Base2,10Base5 34. Guided Media Fiber-Optic CableFiber-optic cable transmit signals in the form of light. Bending of light ray 35. Bending of light ray Angle of Incidence (I): the angle the ray makeswith the line perpendicular to the interfacebetween the two substances Critical Angle: the angle of incidence whichprovides an angle of refraction of 90-degrees. 36. Guided Media Fiber-Optic Cable Optic Fiber 37. Optical fiber Uses reflection toguide light through achannel Core is of glass orplastic surrounded byCladding Cladding is of lessdense glass or plastic 38. Optical Fiber 39. Optical Fiber - Benefits greater capacity data rates of hundreds of Gbps smaller size & weight lower attenuation electromagnetic isolation greater repeater spacing 10s of km at least 40. Optical Fiber - Benefits The following characteristics distinguish optical fiber from twisted pair or coaxial cable: Greater capacity: The potential bandwidth, and hence data rate, of optical fiber isimmense; data rates of hundreds of Gbps over tens of kilometers have beendemonstrated. Compare this to the practical maximum of hundreds of Mbps overabout 1 km for coaxial cable and just a few Mbps over 1 km or up to 100 Mbps to 10Gbps over a few tens of meters for twisted pair. Smaller size and lighter weight: Optical fibers are considerably thinner than coaxialcable or bundled twisted-pair cable. For cramped conduits in buildings andunderground along public rights-of-way, the advantage of small size is considerable.The corresponding reduction in weight reduces structural support requirements. Lower attenuation: Attenuation is significantly lower for optical fiber than for coaxialcable or twisted pair, and is constant over a wide range. Electromagnetic isolation: Optical fiber systems are not affected by externalelectromagnetic fields. Thus the system is not vulnerable to interference, impulsenoise, or crosstalk. By the same token, fibers do not radiate energy, so there is littleinterference with other equipment and there is a high degree of security fromeavesdropping. In addition, fiber is inherently difficult to tap. Greater repeater spacing: Fewer repeaters mean lower cost and fewer sources oferror. The performance of optical fiber systems from this point of view has beensteadily improving. Repeater spacing in the tens of kilometers for optical fiber iscommon, and repeater spacings of hundreds of kilometers have been demonstrated. 41. Optical Fiber - TransmissionCharacteristics uses total internal reflection to transmit light effectively acts as wave guide for 1014 to 1015 Hz can use several different light sources Light Emitting Diode (LED) cheaper, wider operating temp range, lasts longer Injection Laser Diode (ILD) more efficient, has greater data rate relation of wavelength, type & data rate 42. Guided Media Fiber-Optic CablePropagation Modes 43. Guided Media Fiber-Optic CablePropagation Modes 44. Optical Fiber Transmission Modes 45. Guided Media Fiber-Optic CableFiber Construction 46. Guided Media Fiber-Optic CableFiber-optic Cable Connectors 47. Guided Media Optical Fiber Cable Applications: Backbone networks SONET Cable TV backbone LAN 100Base-FX network (Fast Ethernet) 100Base-X 48. Transmission Characteristics ofGuided MediaFrequency TypicalTypicalRepeaterRange Attenuation Delay SpacingTwisted pair 0 to 3.5 kHz 0.2 dB/km @50 s/km2 km(with loading)1 kHzTwisted pairs0 to 1 MHz 0.7 dB/km @5 s/km 2 km(multi-pair 1 kHzcables)Coaxial cable0 to 500 MHz 7 dB/km @ 10 4 s/km 1 to 9 kmMHzOptical fiber186 to 370 0.2 to 0.5 5 s/km 40 km THzdB/km 49. Comparison of Physical Media 50. Electromagnetic Spectrum 51. Wireless Transmission Frequencies 2GHz to 40GHz microwave highly directional point to point satellite 30MHz to 1GHz omnidirectional broadcast radio 3 x 1011 to 2 x 1014 infrared local 52. Unguided Media Propagation Methods 53. Bands 54. Unguided MediaWireless transmission waves 55. Broadcast Radio radio is 3kHz to 300GHz use broadcast radio, 30MHz - 1GHz, for: FM radio UHF and VHF television is omnidirectional still need line of sight suffers from multipath interference reflections from land, water, other objects 56. Unguided Media Radio WavesOmnidirectional Antenna Frequencies between 3 KHz and 1 GHz. are used for multicasts communications, such as radio and television, and paging system. 57. Terrestrial Microwave used for long haul telecommunications and short point-to-point links requires fewer repeaters but line of sight use a parabolic dish to focus a narrow beam onto areceiver antenna 1-40GHz frequencies higher frequencies give higher data rates main source of loss is attenuation distance, rainfall also interference 58. Unguided Media Microwaves Frequencies between 1 and 300 GHz. Used for unicast communication such as cellular phones, satellitenetworks and wireless LANs. Unidirectional Antenna 59. Satellite Microwave satellite is relay station typically requires geo-stationary orbit height of 35,784km spaced at least 3-4 apart typical uses television long distance telephone private business networks global positioning 60. Unguided Media Infrared Frequencies between 300 GHz to 400 THz. Can not penetrate walls.Used for short-range communication in aclosed area using line-of-sight propagation. 61. Infrared modulate noncoherent infrared light end line of sight (or reflection) are blocked by walls no licenses required typical uses TV remote control IRD port 62. Antennas electrical conductor used to radiate or collectelectromagnetic energy transmission antenna radio frequency energy from transmitter converted to electromagnetic energy byy antenna radiated into surrounding environment reception antenna electromagnetic energy impinging on antenna converted to radio frequency electrical energy fed to receiver same antenna is often used for both purposes 63. Radiation Pattern power radiated in all directions not same performance in all directions as seen in a radiation pattern diagram an isotropic antenna is a (theoretical) point in space radiates in all directions equally with a spherical radiation pattern 64. Antenna Gain measure of directionality of antenna power output in particular direction verses thatproduced by an isotropic antenna measured in decibels (dB) results in loss in power in another direction effective area relates to size and shape related to gain 65. Satellite Point to Point Link 66. Satellite Broadcast Link 67. Wireless PropagationGround Wave 68. Wireless PropagationSky Wave 69. Wireless PropagationLine of Sight 70. Line of Sight Transmission Free space loss loss of signal with distance Atmospheric Absorption from water vapour and oxygen absorption Multipath multiple interfering signals from reflections Refraction bending signal away from receiver 71. Multipath Interference 72. Comparison of Media Medium Cost Speed Atten Interfere Security UTPLow 1-100M High High Low STP Medium 1-150M High MediumLow Coax Medium 1M1G Medium Medium Low Fibre High 10M2G Low Low High Radio Medium 1-10M Varies High Low Microw High 1M10G Varies High Medium Satellite High 1 M10G Varies HighMedium Cellular High 9.619.2K Low MediumLow