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DATA COMMUNICATION ( ela …)

DATA COMMUNICATION ( ela …). TRANSMISSION MEDIA. Transmission Media - Overview. Transmission Medium Physical path between transmitter and receiver Guided Media Waves are guided along a solid medium Unguided Media Provides means of transmission but does not guide electromagnetic signals

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DATA COMMUNICATION ( ela …)

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  1. DATA COMMUNICATION(ela…) TRANSMISSION MEDIA

  2. Transmission Media - Overview • Transmission Medium • Physical path between transmitter and receiver • Guided Media • Waves are guided along a solid medium • Unguided Media • Provides means of transmission but does not guide electromagnetic signals • Employ an antenna for transmission

  3. Transmission Media - Overview • Characteristics and quality determined by medium and signal • For guided • For unguided • Key concerns are

  4. Design Factors • Bandwidth • All other factors remaining constant, higher bandwidth gives higher data rate • Transmission impairments • Attenuation • Interference • Number of receivers • In guided media • More receivers (multi-point) introduce more attenuation

  5. Electromagnetic Spectrum

  6. Transmission Characteristics • Guided Media

  7. Transmission Media • Guided media • Twisted-pair • Coaxial Cable • Optical Fiber • Unguided media • Satellites • Terrestrial Microwave • Broadcast Radio

  8. Guided Transmission Media • Transmission Capacity • Either in terms of • Bandwidth, or • Data Rate • Depends critically on • Distance • Type of medium • Point-to-point • Mutipoint

  9. Twisted Pair • Most common medium • Two insulated wires twisted together in a helical manner (like DNA) • Advantages • Disadvantages

  10. Twisted Pair • Separately insulated • Often bundled into cables • Usually installed in buildings during construction

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

  12. Twisted Pair - Transmission Characteristics • Analog • Amplifiers every 5 km to 6 km • Digital • Use either analog or digital signals • Repeater every 2 km or 3 km • Limited in • Distance • Bandwidth (1 MHz) • Data rate (100 Mbps) • Susceptible to interference and noise

  13. Unshielded and Shielded TP • Unshielded Twisted Pair (UTP) • Ordinary telephone wire • Cheapest • Easiest to install • Suffers from external Electromagnetic (EM) interference • Shielded Twisted Pair (STP) • Metal braid or sheathing that reduces interference • More expensive • Harder to handle (thick, heavy)

  14. UTP vs. STP

  15. UTP Categories • Cat 3 • Up to 16 MHz • Voice grade found in most offices • Twist length of 7.5 cm to 10 cm • Cat 4 • Up to 20 MHz • Cat 5 • Up to 100 MHz • Commonly pre-installed in new office buildings • Twist length 0.6 cm to 0.85 cm

  16. Comparison of UTP & STP

  17. http://www.cabletesting.com Near End Crosstalk (NEXT) • Coupling of signal from one pair to another • The tighter the twist in the cable, the more effective the cancellation

  18. Coaxial Cable Applications • Most versatile medium

  19. Coaxial Cable Applications • Television distribution • Cable TV • Long distance telephone transmission • Can carry 10,000 voice calls simultaneously • Being replaced by fiber optic • Short distance computer systems links • LANs

  20. Coaxial Cable - Transmission Characteristics • Analog • Amplifiers every few km • Closer if higher frequency • Up to 500 MHz • Digital • Repeater every 1 km • Closer for higher data rates

  21. Optical Fiber • Greater capacity • Data rates of hundreds of Gbps • Smaller size & weight • Lower attenuation • Electromagnetic isolation • Greater repeater spacing • 10s of km at least

  22. Optical Fiber • System components: • Transmission medium - fiber optic cable • Light source - LED or laser diode • Detector - photodiode

  23. Optical Fiber - Applications • Telephone Network Applications • Long-haul, metropolitan, rural, and subscriber loop circuits • Local Area Networks • Optical fiber networks • Data rates from 100 Mbps to 1 Gbps • Support hundreds (or even thousands) of stations

  24. Optical Fiber - Transmission Characteristics • Light Sources • Light Emitting Diode (LED) • Cheaper • Wider operating temp range • Last longer • Injection Laser Diode (ILD) • More efficient • Greater data rate • Wavelength Division Multiplexing

  25. Attenuation in Guided Media

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