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Transmission Media

Transmission Media. Wired Coaxial Twisted Pair (UTP / STP) Optical Fibres Wireless IR Microwave signals Radio Frequency. Wired LAN (Coaxial cable) high capacity communication cable using BNC Connector 2 concentric conductor one inner (inner core) one outer (metal mesh)

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Transmission Media

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  1. Transmission Media • Wired • Coaxial • Twisted Pair (UTP / STP) • Optical Fibres • Wireless • IR • Microwave signals • Radio Frequency

  2. Wired LAN (Coaxial cable) • high capacity communication cable • using BNC Connector • 2 concentric conductor • one inner (inner core) • one outer (metal mesh) • nowadays mostly for cable TV transmission • disadv : • much thicker • not flexible • more expensive (c.f. UTP / STP)

  3. Wired LAN (Twisted pair) • Using ordinary copper wire • the copper wires are twisted together • to reduce crosstalk / electromagnetic interference • by electrical appliances (motors, transformers) • radio frequency interference • if the twisted pair is • enclosed inside a shield • STP • not enclosed inside a shield (unshield) • UTP • nowadays mostly for networking cabling

  4. Wired LAN (Twisted pair) … cont’d • Using RJ45 connector • Adv : • more flexible • less expensive (c.f. coaxial cable) • Categories • Cat. 1 --- for analogue voice (old telephone system) • Cat. 2 • Cat. 3 --- 10baseT Ethernet (16Mbps) • Cat. 4 • Cat. 5 --- 100baseT Ethernet (100Mbps) • Ref : http://www.siemon.com/us/standards/13-10_twisted-pair_balanced_cabling.asp

  5. Wired LAN (Twisted pair) … cont’d • Types of cables • Straight through cable • connecting PC to network devices (hub / switch) • Crossover cable • connection between PC & PC • connection between network device with network device • Rollover cable • with connector • RJ45 to DB-9 converter then to COM 1 or COM 2 of PC

  6. Wired LAN (Optical fibres) • made up of a bundle of thin tubes of glass • thinner than a human hair • do not conduct or transmit electrical signals • not interfere by electromagnetic wave • Transmission of info via light pulse • Carry more info than copper wire at the same period of time • signal can travel a very long distance • because no / little attenuation • But fragile … need more protection • installation .. More labour intensive

  7. Interference • Original Signal

  8. Noise

  9. When signal and noise combined together

  10. Resulting Signal detected

  11. Wireless LAN • use electromagnetic waves to transmit and receive data from one device to another • suitable to env. where cabling is difficult / not practical / not economical • construction site • warehouse • school campus • hospitals • usually as an extension or an alternative for a wired LAN • transmitter : Access Point (AP)

  12. Wireless LAN … cont’d • Using IR / radio signals / microwaves • Some of them require direct line of sight (e.g. : IR) • Signal travels in straight line • Stations using antenna & satellite • To avoid the • curvature of the Earth • Mountains • Tall buildings • Other signal obstacles • Advanced wireless technology • Eliminate the limitation of direct line-of-sight • More flexible

  13. Wireless LAN … cont’d • Problems faced by wireless transmission • Signals can be weakened by bad weather and solar activity • A satellite can be used for around 7-10 years • Anyone can detect the signal (Security problem) • Signal / data must be encrypted before sending

  14. Wireless LAN … cont’d • Advantages • Easy installation • Flexibility in usage • Economical • Expandability • http://iclassroom.hkedcity.net/directory/index.phtml?iroom_id=1387&tool_id=853&folder_id=1520

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