1/21 Chapter 4 – Transmission Media

2/21 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

3/21 Design Factors  A number of design factors relating to the transmission media and the signal determine the data rate and distance 1.bandwidth  higher bandwidth gives higher data rate 2.transmission impairments  e.g. attenuation limit the distance 3.Interference  from other signals in overlapping frequency bands 4.number of receivers in guided media  more receivers introduces more attenuation

4/21 Electromagnetic Spectrum

5/21 Transmission Characteristics of Guided media 186 to 370 THz 0.2 to 0.5 dB/km Frequency Range Typical Attenuation Typical Delay Repeater Spacing Twisted pairs (multi-pair cables) 0 to 1 MHz0.7 1 kHz 5 µs/km2 km Coaxial cable0 to 500 MHz7 10 MHz 4 µs/km1 to 9 km Optical fiber5 µs/km40 km

6/21 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

Twisted Pair: Transmission Characteristics 7/21  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

8/45 Attenuation vs frequency for the guided media

9/21 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

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

11/21 Comparison Between Unshielded and Shielded Twisted Pair

12/21 Coaxial Cable

13/21 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

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

15/21 Optical Fiber

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

17/21 Optical Fiber: Transmission Characteristics  uses total internal reflection to transmit light  effectively acts as wave guide for to 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

18/21 Optical Fiber Transmission Modes

19/21 Frequency Utilization for Fiber Application

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

21/21 Optical Fiber : Applications