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3. transmission media


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3. transmission media

  1. 1. Transmission Media ( Guided and Wireless Transmission ) Pg 128
  2. 2. Overview <ul><li>Guided – provide a physical path along which the signals are propagated </li></ul><ul><ul><li>Wire: Coaxial Cable, Optical Fiber, Twisted Pair </li></ul></ul><ul><li>Unguided –employ an antenna for transmitting through air, vacuum or water. </li></ul><ul><ul><li>wireless </li></ul></ul><ul><li>Characteristics and quality determined by medium and signal </li></ul><ul><ul><li>For guided, the medium is more important </li></ul></ul><ul><ul><li>For unguided, the bandwidth produced by the antenna is more important </li></ul></ul><ul><li>Key concerns are data rate and distance </li></ul>Key Points
  3. 3. Design Factors <ul><li>Bandwidth </li></ul><ul><ul><li>Higher bandwidth gives higher data rate </li></ul></ul><ul><li>Transmission impairments </li></ul><ul><ul><li>Attenuation </li></ul></ul><ul><li>Interference </li></ul><ul><li>Number of receivers </li></ul><ul><ul><li>In guided media </li></ul></ul><ul><ul><li>More receivers (multi-point) introduce more attenuation </li></ul></ul>
  4. 4. Electromagnetic Spectrum
  5. 5. 2.2.1 Guided Transmission Media <ul><li>To become part of network, a PC uses a network interface card (NIC). </li></ul><ul><li>(For portable comp., NIC can be in form of a PC Card/ USB adapter ) </li></ul><ul><li>Backbone ,connection leading to and from it might use: </li></ul><ul><li>Twisted Pair </li></ul><ul><li>Coaxial cable </li></ul><ul><li>Optical fiber </li></ul>PC’s RAM NIC LAN’s backbone signal signal
  6. 6. Transmission Characteristics of Guided Media     Frequency Range Typical Attenuation Typical Delay Repeater Spacing Twisted pair (with loading) 0 to 3.5 kHz 0.2 dB/km @ 1 kHz 50 µs/km 2 km Twisted pairs (multi-pair cables) 0 to 1 MHz 0.7 dB/km @ 1 kHz 5 µs/km 2 km Coaxial cable 0 to 500 MHz 7 dB/km @ 10 MHz 4 µs/km 1 to 9 km Optical fiber 186 to 370 THz 0.2 to 0.5 dB/km 5 µs/km 40 km
  7. 7. Twisted Pair – Physical Description
  8. 8. Twisted Pair - Applications <ul><li>Most common transmission medium for analog/digital signal </li></ul><ul><li>Telephone network </li></ul><ul><ul><li>Between house and local tel. exchange (subscriber loop) </li></ul></ul><ul><li>Com. within buildings </li></ul><ul><ul><li>To private branch exchange (PBX) </li></ul></ul><ul><li>For local area networks (LAN) </li></ul><ul><ul><li>10Mbps or 100Mbps </li></ul></ul>
  9. 9. Twisted Pair - Pros and Cons <ul><li>Pros </li></ul><ul><li>Cheap </li></ul><ul><li>Easy to work with </li></ul><ul><li>Cons </li></ul><ul><li>Low data rate </li></ul><ul><li>Short range </li></ul>
  10. 10. Twisted Pair - Transmission Characteristics <ul><li>Analog </li></ul><ul><ul><li>Amplifiers every 5km to 6km </li></ul></ul><ul><li>Digital </li></ul><ul><ul><li>Use either analog or digital signals </li></ul></ul><ul><ul><li>repeater every 2km or 3km </li></ul></ul><ul><li>Limited distance </li></ul><ul><li>Limited bandwidth (1MHz) </li></ul><ul><li>Limited data rate (100MHz) </li></ul><ul><li>Susceptible to interference and noise </li></ul>
  11. 11. Coaxial Cable - Physical Description
  12. 12. Coaxial Cable - Applications <ul><li>Most versatile medium </li></ul><ul><li>Television distribution </li></ul><ul><ul><li>Arial to TV </li></ul></ul><ul><ul><li>Cable TV </li></ul></ul><ul><li>Long distance telephone transmission </li></ul><ul><ul><li>Can carry 10,000 voice calls simultaneously </li></ul></ul><ul><ul><li>Being replaced by fiber optic </li></ul></ul><ul><li>Short distance computer systems links </li></ul><ul><ul><li>Connections between devices </li></ul></ul><ul><li>Local area networks </li></ul>
  13. 13. Coaxial Cable - Benefits <ul><li>Less susceptible to interference and crosstalk** </li></ul><ul><li>Longer distance** </li></ul><ul><li>**(compared to twisted pair) </li></ul><ul><li>Wide variety of application </li></ul>
  14. 14. Coaxial Cable - Transmission Characteristics <ul><li>Analog </li></ul><ul><ul><li>Amplifiers every few km </li></ul></ul><ul><ul><li>Closer if higher frequency </li></ul></ul><ul><ul><li>Up to 500MHz </li></ul></ul><ul><li>Digital </li></ul><ul><ul><li>Repeater every 1km </li></ul></ul><ul><ul><li>Closer for higher data rates </li></ul></ul>
  15. 15. Optical Fiber - Physical Description
  16. 16. Optical Fiber - Benefits <ul><li>Greater capacity </li></ul><ul><ul><li>Data rates of hundreds of Gbps </li></ul></ul><ul><li>Smaller size & weight </li></ul><ul><li>Lower attenuation </li></ul><ul><li>Electromagnetic isolation </li></ul><ul><ul><li>Not affected by external electromagnetic fields </li></ul></ul><ul><li>Greater repeater spacing </li></ul><ul><ul><li>10s of km at least </li></ul></ul>
  17. 17. Optical Fiber - Applications <ul><li>Tel. network </li></ul><ul><li>Long-haul trunks (laluan) </li></ul><ul><ul><li>aver. 1500 km, 20k-60k voice channels </li></ul></ul><ul><li>Metropolitan trunks </li></ul><ul><li>aver. 12 km, 100k voice channels </li></ul><ul><li>Rural exchange trunks </li></ul><ul><ul><li>Links town-village 40-160 km </li></ul></ul><ul><li>Subscriber (Pelanggan) loops </li></ul><ul><ul><li>Central exchange - subsciber </li></ul></ul><ul><li>LANs </li></ul><ul><ul><li>100 Mbps to 1Gbps </li></ul></ul>
  18. 18. Optical Fiber Transmission Modes
  19. 19. Wireless Transmission Frequencies <ul><li>2GHz to 40GHz </li></ul><ul><ul><li>Microwave frequencies </li></ul></ul><ul><ul><ul><li>Highly directional (one way) </li></ul></ul></ul><ul><ul><ul><li>Point to point transmission </li></ul></ul></ul><ul><ul><ul><li>Satellite </li></ul></ul></ul><ul><li>30MHz to 1GHz ( radio range ) </li></ul><ul><ul><li>Omnidirectional </li></ul></ul><ul><ul><li>Broadcast radio </li></ul></ul><ul><li>3 x 10 11 to 2 x 10 14 Hz </li></ul><ul><ul><li>Infrared </li></ul></ul>
  20. 20. Antennas <ul><li>Electrical conductor (or system of conductor) used to radiate electromagnetic energy or collect electromagnetic energy </li></ul><ul><li>Transmission of signal </li></ul><ul><ul><li>Radio-frequency electrical energy from transmitter </li></ul></ul><ul><ul><li>Converted to electromagnetic energy </li></ul></ul><ul><ul><li>By antenna </li></ul></ul><ul><ul><li>Radiated into surrounding environment; atmosphere, space, water </li></ul></ul><ul><li>Reception of signal </li></ul><ul><ul><li>Electromagnetic energy impinging(melanggar) on antenna </li></ul></ul><ul><ul><li>Converted to radio-frequency electrical energy </li></ul></ul><ul><ul><li>Fed to receiver </li></ul></ul><ul><li>Same antenna often used for both </li></ul>
  21. 21. Terrestrial Microwave <ul><li>Parabolic dish </li></ul><ul><li>Long haul telecommunications (application) </li></ul><ul><ul><li>alternative to coaxial cable or optical fiber. </li></ul></ul><ul><ul><li>requires far fewer amplifiers/repeaters than coaxial cable over the same distance but requires LOS (line-of -sight) transmission. </li></ul></ul><ul><li>Higher frequencies give higher data rates </li></ul><ul><ul><li>common frequencies used for transmission are in the range 1 to 40GHz. </li></ul></ul>
  22. 22. Satellite Microwave <ul><li>Satellite is relay station </li></ul><ul><li>Satellite receives on one frequency (uplink), amplifies or repeats signal and transmits on another frequency (downlink) </li></ul><ul><li>Applications </li></ul><ul><ul><li>Television </li></ul></ul><ul><ul><li>Long distance telephone </li></ul></ul>
  23. 23. Satellite Point to Point Link Uplink Downlink
  24. 24. Satellite Broadcast Link
  25. 25. Broadcast Radio <ul><li>Omnidirectional </li></ul><ul><li>FM radio </li></ul><ul><li>UHF and VHF television </li></ul><ul><li>Suffers from multipath interference </li></ul><ul><ul><li>Reflections </li></ul></ul>
  26. 26. Infrared <ul><li>Achieved using transmitter/receivers (transceiver) that modulate non-coherent infrared light </li></ul><ul><li>Transceivers must be within the line of sight of each other either directly or via reflection form a light-colored surface such as the ceiling of a room. </li></ul><ul><li>Blocked by walls </li></ul><ul><li>e.g. TV remote control </li></ul>
  27. 27. Wireless Propagation <ul><li>Signal travels along three routes </li></ul><ul><ul><li>Ground wave </li></ul></ul><ul><ul><ul><li>Follows contour of earth </li></ul></ul></ul><ul><ul><ul><li>Up to 2MHz </li></ul></ul></ul><ul><ul><ul><li>Best-known example of ground wave communication is AM radio </li></ul></ul></ul><ul><ul><li>Sky wave </li></ul></ul><ul><ul><ul><li>Used for amateur radio, BBC world service, Voice of America </li></ul></ul></ul><ul><ul><ul><li>A signal from an earth-based antenna is reflected from ionosphere layer of upper atmosphere back down to earth. </li></ul></ul></ul><ul><ul><li>Line of sight (LOS) </li></ul></ul><ul><ul><ul><li>Above 30Mhz, neither ground wave or sky wave propagation modes operate, and communication must be by LOS. </li></ul></ul></ul>
  28. 28. Line of Sight Transmission’s Impairment <ul><li>Free space loss </li></ul><ul><ul><li>Signal disperses with distance (signal spread over a larger and larger area) </li></ul></ul><ul><li>Atmospheric Absorption </li></ul><ul><ul><li>Water vapour and oxygen absorb radio signals </li></ul></ul><ul><ul><li>Water greatest at 22GHz, less below 15GHz </li></ul></ul><ul><ul><li>Oxygen greater at 60GHz, less below 30GHz </li></ul></ul><ul><ul><li>Rain and fog scatter radio waves that results in attenuation. </li></ul></ul><ul><li>Multipath </li></ul><ul><ul><li>Better to get line of sight if possible </li></ul></ul><ul><ul><li>Signal can be reflected causing multiple copies to be received </li></ul></ul><ul><ul><li>May be no direct signal at all </li></ul></ul><ul><ul><li>May reinforce or cancel direct signal </li></ul></ul><ul><li>Refraction </li></ul><ul><ul><li>May result in partial or total loss of signal at receiver </li></ul></ul>END!!
  29. 29. Ground Wave Propagation
  30. 30. Sky Wave Propagation
  31. 31. Line of Sight Propagation
  32. 32. Free Space Loss
  33. 33. Multipath Interference
  34. 34. Key Points <ul><li>Transmission media – guided and unguided </li></ul><ul><li>For guided transmission: </li></ul><ul><ul><li>Twisted pair has been the workhorse for com. of all sorts. </li></ul></ul><ul><ul><li>Higher data rates over longer distances can be achieved with coaxial cable, so coaxial cable has been often been used for high-speed LAN and for high-capacity long-distance trunk applications. </li></ul></ul>
  35. 35. Key Points(2) <ul><ul><li>However, tremendous capacity of optical fiber has made that medium more attractive than coaxial cable, and thus optical fiber has taken over much of the market for high-speed LANs and for long-distance applications. </li></ul></ul><ul><li>For unguided transmission: </li></ul><ul><ul><li>Commonly used for info. com. including broadcast radio, terrestrial ( daratan ) microwave, and satellite. Infrared transmission is used in some LAN applications. </li></ul></ul>
  36. 36. Local Telephone Exchange <ul><li>A telephone exchange is the place that users voice and broadband is delivered to and from to their address. </li></ul><ul><li>The exchange splits the signals that it receives so it can then send them on to the correct part of the exchange. Voice calls are sent to the PSTN ( P ublic S witched T elephone N etwork) network and broadband/ADSL signals is sent to the DSLAM ( D igital S ubscriber L ine A ccess M ultiplexer). </li></ul>
  37. 37. private branch exchange <ul><li>A PBX (private branch exchange) is a telephone system within an enterprise that switches calls between enterprise users on local lines while allowing all users to share a certain number of external phone lines. The main purpose of a PBX is to save the cost of requiring a line for each user to the telephone company's central office. </li></ul>