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Computer Network and Infrastructure Transmission Media

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  1. Computer Network and InfrastructureTransmission Media Dr. E.C. Kulasekere

  2. Section Objectives • Understand the principles behind media selection. • The different types of guided media • The different types of unguided media • Understand the uses and applications of such media. APIIT - 2004

  3. Transmission Media • The characteristics and quality of a data transmission is determine by both the characteristics of the medium and the characteristics of the signal. • The key concerns of transmission • Data rate • Distance of tx. APIIT - 2004

  4. Media Design Factors • Bandwidth • Higher bandwidth gives higher data rate • Transmission impairments • Attenuation limits the distance of transmission • Interference • Particularly for unguided media with overlapping frequencies. • Number of receivers • In guided media • More receivers (multi-point) introduce more attenuation APIIT - 2004

  5. Classification of Media • Guided Transmission Media • Conductive Metal • Glass or Plastic • Wireless Transmission Media • Ground wave • Sky wave • Line-of-sight APIIT - 2004

  6. Electromagnetic Spectrum APIIT - 2004

  7. Guided Transmission MediaConductive Metal • Twisted Pair Cables (TP) • Shielded Twisted Pair (STP) • Unshielded Twisted Pair (UTP) • UTP Data Transmission Categories • Category 3 (up to 16 MHz) • Category 4 (up to 20 MHz) • Category 5 (up to 100 MHz) APIIT - 2004

  8. Conductive MetalTwisted Pair Cables UTP STP APIIT - 2004

  9. Conductive MetalShielded Twisted Pair Cables APIIT - 2004

  10. Conductive MetalTwisted Pair … • The twisting is done to reduce cross talk. • Neighboring pairs may have different twist lengths. APIIT - 2004

  11. Twisted Pair Applications • Most common medium • Telephone network • Between house and local exchange (subscriber loop) • Within buildings • To private branch exchange (PBX) • For local area networks (LAN) • 10Mbps or 100Mbps APIIT - 2004

  12. Conductive MetalCoaxial Cables • Functionally Grouped into: • Baseband: cable dedicated for only one channel • Broadband: cable can carry several analog signals (at different frequencies) simultaneously. APIIT - 2004

  13. Conductive MetalCoaxial Cable Physical Layout APIIT - 2004

  14. Coaxial Cable Applications • Most versatile medium • Television distribution • Ariel to TV • Cable TV • Long distance telephone transmission • Can carry 10,000 voice calls simultaneously • Being replaced by fiber optic • Short distance computer systems links • Local area networks APIIT - 2004

  15. Optical Fiber APIIT - 2004

  16. 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 APIIT - 2004

  17. Wireless Transmission • Unguided media • Transmission and reception via antenna • Directional • Focused beam • Careful alignment required • Omnidirectional • Signal spreads in all directions • Can be received by many antennae APIIT - 2004

  18. Wireless Transmission MediaTerrestrial Microwave APIIT - 2004

  19. Wireless Transmission MediaSatellites APIIT - 2004

  20. Wireless Transmission MediaGeostationary Satellites APIIT - 2004

  21. Wireless Transmission MediaOther Media • Broadcast Radio • Covers VHF and part of the UHF • Covers FM radio and UHF television • Infrared • Line of sight • Omni directional • Lasers APIIT - 2004

  22. Review Questions • What are some major advantages and disadvantages of microwave transmission? • Point-to-point microwave transmission has a high data rate and less attenuation than twisted pair or coaxial cable. It is affected by rainfall, however, especially above 10 GHz. It is also requires line of sight and is subject to interference from other microwave transmission, which can be intense in some places. APIIT - 2004

  23. Review Questions • Why must a satellite have distinct uplink and downlink frequencies? • In order to avoid interference from the uplink and downlink signals • Indicate some significant differences between broadcast radio and microwave. • Broadcast is omnidirectional, does not require dish shaped antennas, and the antennas do not have to be rigidly mounted in precise alignment. APIIT - 2004

  24. Review Problems • Given a 100W power source, what is the maximum allowable length for the following transmission media if a signal of 1W is to be received? • 24-gauge (0.5mm) twisted wire operating at 300kHz • 24-gauge (0.5mm) twisted wire operating at 1MHz • 0.375in (9.5mm) coaxial cable operating at 1MHz • 0.375in (9.5mm) coaxial cable operating at 25MHz • Optical fiber operating at its optimal frequency. APIIT - 2004

  25. Review Problems The allowable power loss is 10 ´ log 100 = 20 dB a. From Figure in next page, the attenuation is about 13 dB per km. Length = (20 dB)/(13 dB per km) = 1.5 km b. Length = (20 dB)/(20 dB per km) = 1 km c. Length = (20 dB)/(2.5 dB per km) = 8 km d. Length = (20 dB)/(10 dB per km) = 2 km e. Length = (20 dB)/(0.2 dB per km) = 100 km APIIT - 2004

  26. APIIT - 2004