( Transmission media (chapter 4

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William Stallings Data and Computer Communications Chapter 4 Transmission Media 

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Overview I Guided - wire Unguided - wireless Characteristics and quality determined by medium and signal For guided, the medium is more important For unguided, the bandwidth produced by the antenna is more important Key concerns are data rate and distance oo نار بح oa 

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Design Factors 0 Bandwidth I Higher bandwidth gives higher data rate 0 Transmission impairments I Attenuation 0 Interference 0 Number of receivers I In guided media I More receivers (multi-point) introduce more attenuation 

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Electromagnetic Spectrum Frequency ‏”صر كمسر صر “مر حمر غوف اه‎ too?! ‏کر خر‎ OC STS 01 ‏آ‎ ‎4a‏ 4 ليم ‎Power and ielephone Radio Microwave ‏هه‎ | ‎owing erator Radios and wears agar ‏سس‎ 1 ‏ی ی و و جم + ‎Twisted‏ 3 ‏این ‎Tiber‏ ‎‘axial Cable >|‏ ۴ ‎<«t+>| «‏ ‎NwtRadio | Wat Rdio) Tereesctat‏ ‎and 1 | and Satelite‏ ‎Transmission‏ ‏1 1 | 1 1 | 1 | 1 1 1 1 ‏كر ۱0 مر ور حور كور “را لبر تا ‎oF‏ کر کر ‎Wavelength”‏ ‎inspace‏ ‎meters) ‎ELF =Extemely low fequoney MF =Madium froquency UE = Utteahigh ‏مسو‎ ‎VE_ = Yoive frequency HF =Hightrequency— SHP = Superhigh fegueney ‎VLE ‏عدوم ها و‎ VHF = Very high frequency EHF = Extremely ‏دسم كيلا‎ ‎LF = Low frequency ‎ ‎ ‎ ‎ ‎ ‎ ‎ 

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Guided Transmission Media 0 Twisted Pair 1 Coaxial cable 0 Optical fiber 

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Twisted Pair twist ton OO a cag cage —Often "bundled —Usually installed in building during construction (a) Twisted pair 

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Twisted Pair - Applications 0 Most common medium 0 Telephone network | Between house and local exchange (subscriber loop) 0 Within buildings I To private branch exchange (PBX) U For local area networks (LAN) 1 10Mbps or 100Mbps 

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Twisted Pair - Pros and Cons 0 Cheap 0 Easy to work with 0 Low data rate 0 Short range 

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Twisted Pair - Transmission Characteristics 0 Analog 1١ Amplifiers every 5km to 6km 0 Digital I Use either analog or digital signals I repeater every 2km or 3km 0 Limited distance 0 Limited bandwidth (1MHz) U Limited data rate (LOOMHz) 0 Susceptible to interference and noise 

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Unshielded and Shielded TP 0 Unshielded Twisted Pair (UTP) ! Ordinary telephone wire I Cheapest I Easiest to install | Suffers from external EM interference U Shielded Twisted Pair (STP) I Metal braid or sheathing that reduces interference I More expensive | Harder to handle (thick, heavy) 

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UTP Categories 0 Cat 3 I up to 16MHz I Voice grade found in most offices ۱ Twist length of 7.5 cm to 10 cm 0 Cat 4 I up to 20 MHz 0 Cat 5 I up to LOOMHz 1 Commonly pre-installed in new office buildings I Twist length 0.6 cm to 0.85 cm 

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Near End Crosstalk Coupling of signal from one pair to another Coupling takes place when transmit signal entering the link couples back to receiving pair i.e. near transmitted signal is picked up by near receiving pair ص ص ص 

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Coaxial Cable Outer conductor Outer sheath Insulatior Inner conductor —Outer conductor is braided shield —Inner conductor is solid metal ‘Separated by insulating material —Covered by padding 

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Coaxial Cable Applications 0 Most versatile medium 0 Television distribution I Ariel to TV | Cable TV 1 Long distance telephone transmission ! Can carry 10,000 voice calls simultaneously | Being replaced by fiber optic 0 Short distance computer systems links 0 Local area networks 

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Coaxial Cable - Transmission Characteristics 0 Analog I Amplifiers every few km ! Closer if higher frequency I Up to 500MHz 1 Digital ۱ Repeater every 1km I Closer for higher data rates 

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Optical Fiber Jacket Core Cladding —Glass or plastic core 4 —Laser or light emitting diode Light at less than incidence —Specially designed jacket ciritical angle is absorbed in jacket 

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Optical Fiber - Benefits 0 Greater capacity I Data rates of hundreds of Gbps 0 Smaller size & weight 0 Lower attenuation 0 Electromagnetic isolation 0 Greater repeater spacing I 10s of km at least 

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Optical Fiber - Applications Long-haul trunks Metropolitan trunks Rural exchange trunks Subscriber loops LANs 1 ا 1 1 1 

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Optical Fiber - Transmission Characteristics IT Act as wave guide for 1014 to 1015 Hz I Portions of infrared and visible spectrum 0 Light Emitting Diode (LED) ! Cheaper ! Wider operating temp range I Last longer 0 Injection Laser Diode (ILD) | More efficient ! Greater data rate 0 Wavelength Division Multiplexing 

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Optical Fiber Transmission Modes Input pulse ‏نویه بح‎ pulse (b) Graded-index multimode 

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Wireless Transmission 0 Unguided media 0 Transmission and reception via antenna 0 Directional I Focused beam ! Careful alignment required 0 Omnidirectional I Signal spreads in all directions I Can be received by many antennae 

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Frequencies ] 20۳2 ۵ 72 ! Microwave ! Highly directional I Point to point I Satellite 0 30MHz to 1GHz 1 Omnidirectional ! Broadcast radio 0 3x 1011 to 2 x 1024 ! Infrared ! Local 

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Terrestrial Microwave Parabolic dish Focused beam Line of sight Long haul telecommunications Higher frequencies give higher data rates 1 ا 1 1 1 

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Satellite Microwave 0 Satellite is relay station 0 Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency 0 Requires geo-stationary orbit I Height of 35,784km 0 Television 0 Long distance telephone 0 Private business networks 

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Broadcast Radio 0 Omnidirectional 0 FM radio 0 UHF and VHF television 0 Line of sight 0 Suffers from multipath interference I Reflections 

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Infrared 0 Modulate noncoherent infrared light 0 Line of sight (or reflection) 0 Blocked by walls 0 e.g. TV remote control, IRD port 

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Required Reading 0 Stallings Chapter 4