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Overview of Transmission Media: Guided and Unguided Technologies in Data Communication

This chapter provides a comprehensive overview of transmission media used in data communication, distinguishing between guided (e.g., copper twisted pair, coaxial cable, optical fiber) and unguided (wireless) mediums. It discusses key design factors impacting data rates and distance, such as bandwidth, transmission impairments, and interference. The characteristics of each type of guided medium, including twisted pairs, coaxial cables, and optical fiber, are examined, highlighting their transmission abilities, attenuation, and applications. This guide is essential for understanding the choice of medium in communication systems.

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Overview of Transmission Media: Guided and Unguided Technologies in Data Communication

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  1. Chapter 4 – Transmission Media 1/21

  2. Overview • guided – copper twisted pair, coaxial cable optical fiber • unguided – wireless; through air, vacuum, or water • characteristics and quality determined by medium and transmitted signal • in unguided media - bandwidth of signal produced by the antenna is more important • in guided media - medium is more important • key concerns are data rate and distance 2/21

  3. Design Factors • A number of design factors relating to the transmission media and the signal determine the data rate and distance • bandwidth • higher bandwidth gives higher data rate • transmission impairments • e.g. attenuation limit the distance • Interference • from other signals in overlapping frequency bands • number of receivers in guided media • more receivers introduces more attenuation 3/21

  4. Electromagnetic Spectrum 4/21

  5. Transmission Characteristics of Guided media Frequency Range Typical Attenuation Typical Delay Repeater Spacing 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 5/21

  6. Twisted pair • Twisting tends to decrease the crosstalk interference between adjacent pairs in a cable. • Neighboring pairs in a bundle typically have somewhat different twist lengths to reduce the crosstalk interference • On long-distance links, the twist length varies from 5 to 15 cm 6/21

  7. Twisted Pair: Transmission Characteristics • Analog Transmission • needs amplifiers every 5km to 6km • Digital Transmission • can use either analog or digital signals • needs a repeater every 2-3km • Limited distance • Limited bandwidth (1MHz) • Limited data rate (few Mbps) • Susceptible to interference and noise • e.g., 50/60 Hz power line frequency • Less expensive that coaxial cables and fiber 7/21

  8. Attenuation vs frequency for the guided media 8/45

  9. Unshielded vs Shielded twisted pairs • 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) • In a variety of categories - see the Electronic Industry Association standard EIA-568 9/21

  10. Twisted Pair Categories and Classes UTP = Unshielded Twisted Pair FTP = Foil Twisted Pair (Foil قصدير) SSTP = Shielded Screen Twisted Pair 10/21

  11. Comparison Between Unshielded and Shielded Twisted Pair A t t e n u a ti o n (d B p e r 100 m ) F re qu e n cy Ca t egory 3 Ca t egory 5 ( M H z ) UT P UT P 150 - oh m S T P 1 2 . 6 2 . 0 1 . 1 4 5 . 6 4 . 1 2 . 2 16 13 . 1 8 . 2 4 . 4 25 — 10 . 4 6 . 2 100 — 22 . 0 12 . 3 300 — — 21 . 4 11/21

  12. Coaxial Cable 12/21

  13. Coaxial Cable: Transmission characteristics • superior frequency characteristics to TP • performance limited by attenuation & noise • analog signals • amplifiers every few Km • closer when using higher frequencies • up to 500MHz • digital signals • repeater every 1km • closer for higher data rates 13/21

  14. Coaxial Cable : Applications • Television Distribution (cable TV) • Long distance telephone transmission • Short-run computer system links • Local area networks 14/21

  15. Optical Fiber 15/21

  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 16/21

  17. Optical Fiber: Transmission Characteristics • 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 17/21

  18. Optical Fiber Transmission Modes 18/21

  19. Frequency Utilization for Fiber Application 19/21

  20. Optical Fiber : Applications • Long-haul trunks (1500Km, high capacity: typically 20000-60000 voice channels) • Metropolitan trunks (12 Km, 100000 voice channel in a trunk group) • Rural exchange trunks (40-160 Km, 5000 voice channels) • Subscriber loops (replace twisted pair and coaxial cables, carry voice, data, image and video) • Local area networks (100Mbps-10Gbps) 20/21

  21. Optical Fiber : Applications 21/21

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