Data Communications and Networking PDF

Because learning changes everything.® Chapter 02 Physical Layer Data Communications and Networking, With TCP/IP protocol suite Sixth Edition Behrouz A. Forouzan © 2022 McGraw Hill, LLC. All rights reserved. Authorized only for instructor use in the classroom. N...

Because learning changes everything.® Chapter 02 Physical Layer Data Communications and Networking, With TCP/IP protocol suite Sixth Edition Behrouz A. Forouzan © 2022 McGraw Hill, LLC. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill, LLC. Chapter 2: Outline 2.1 SIGNALS 2.2 SIGNAL IMPAIRMENT physical 2.3 DIGITAL TRANSMISSION 2.4 ANALOG TRANSMISSION Oliger 2.5 MULTIPLEXING 2.6 TRANSMISSION MEDIA © McGraw Hill, LLC 2 Figure 2.1 Communication at the physical layer O g R fob d8 Is ftpI Rooter Network wtf Data physical Loading… Access the text alternative for slide images. © McGraw Hill, LLC 3 2-1 SIGNALS What is exchanged between Alice and Bob is data, but what goes through the network at the physical layer is signals. I DI ft El H J fl I ge g wired 1 If I ft wireless lg't I It © McGraw Hill, LLC 4 Figure 2.2 Comparison of analog and digital signals f Digital blog s Gf 1111 00011111111 0000 I 111 volts I Il l l l s Hb G Loading… ll leu u t.ms el2e.P 1onet 1evelItgoo0v 000 O O da binarystring oHW fillet s A y Periodic Is aperiodic Igf ask.fi Ii is a2 a If 2 Access the text alternative for slide images. © McGraw Hill, LLC mum 5 IH my 2.1.1 Analog Signal An analog signal can take one of the two forms: periodic or aperiodic. In data communication, we normally use periodic signals. A simple periodic signal, a sine wave, cannot be decomposed into simpler signals. WEE Analog signal sine wave periodic signal simple © McGraw Hill, LLC 6 gift 4dB It How WY Figure 2.3 A sine wave www.sina sit no f god 5 hertz X Hgsf Ei ya HiFi Pangfffk 1 g I Too degrees IH e 1 period Seconnydj  Access the text alternative for slide images. © McGraw Hill, LLC 7 Peak Amplitude Mahl y axis I The peak amplitude of a signal is the absolute value of its highest 7 intensity. ix © McGraw Hill, LLC 8 T f Period and Frequency S JH J El T D Id 8 secoundsf I b w j The period (T) refers to the amount of time, in seconds, that a signal needs to complete one cycle. The frequency (f), measured in Hertz (Hz), refers to the number of periods in one second. Note that period and frequency are just one characteristic defined in two ways. Period and frequency are inverse of each other, in other words (f = 1/ T). zP period H freq I © McGraw Hill, LLC s Y 9 Phase a is OUTWITH The term phase describes the position of the waveform relative to time 0. If we think of the wave as something that can be shifted backward or forward along the time axis, phase describes the amount of that shift. © McGraw Hill, LLC 10 Wavelength aperiodic 1421 ble QING W 4 c of f It Is Wld Igf The wavelength is the distance a simple signal can travel in one period. Wavelength binds the period or the frequency of a simple sine wave to the propagation speed in the medium. If we represent wavelength by l, propagation speed by c, and frequency by f, and period by T, we get Loading… period fl WI 416 Chili frequency wired wireless smtgiaisted Hoxie's Effed 39.2 g as is TEST  3 10 l f © McGraw Hill, LLC 11 Time and Frequency Domain I M peak A sine waves is comprehensively defined by its amplitude, frequency, and phase. This can be done in both time and frequency domain. were © McGraw Hill, LLC 12 Figure 2.4 The time-domain and frequency-domain plots of a sine wave Ig 666W visualization I simple I If In g  L frecuencyh of J H © McGraw Hill, LLC Access the text alternative for slide images. jy.bg T.tl 13 His Composite Signal I Dated is So far, we have focused on simple sine waves. A composite signal is made of many simple sine waves. The range of frequencies contained in a composite signal is its bandwidth. The bandwidth of a signal is the difference between the lowest and highest frequencies in the signal. a simple j G.gsjqpj84 jo different es g Composit frequency signal I IT  tho 8 © McGraw Hill, LLC 14 Bandwidth 1 Maxfreq Min freq To The range of frequencies contained in a composite signal is its bandwidth. The bandwidth of a signal is the difference between the lowest and highest frequencies in the signal. The bandwidth of a composite signal is the difference between the highest and the lowest frequencies contained in that signal. is W frequengIIds I  misfffes © McGraw Hill, LLC W'fast 15 2.1.2 Digital Signal Kilo Information can also be represented by a digital signal. For example, a value 1 can be encoded as a positive voltage and a value 0 as zero voltage. A digital signal can have more than two levels. In this case, we can send more than 1 bit for each level. Figure 2.5 shows two signals, one with two levels and the other with four. A swim o tht 0144 period of go 66 i  p © McGraw Hill, LLC 16 Figure 2.5 Two digital signals, one with two and one with four bit- levels 2lends 2 2 4 levels To mmmm  s i Access the text alternative for slide images. © McGraw Hill, LLC 17 Bit Rate Most digital signal are nonperiodic, and thus period and frequency are not appropriate characteristics. Another term-bit rate (instead of frequency) is used. The bit rate is the number of bits sent in 1 second. O w gl Bit fast © McGraw Hill, LLC 18 Example 2.3 I s Iff Assume we have downloaded text documentation at the rate of 100 pages per second. A page is an average of 24 lines with 80 characters per line. If we assume that one character requires 8 bits, the bit rate is: l iE 100 * 24 * 80 * 8 = 1,536,000 bps = 1.536 Mbps char 1byte 8b  fine4 take Far Fts 153f ooo b ps t53bn © McGraw Hill, LLC 19 to Bit Length f Wi wavelength H ioDsi We discuss the concept of a wavelength for an analog signal. We can define something similar for a digital signal:9gintdj the bitffwo length. The bit length is the distance one bit occupy on the transmission medium. s.s bit length = 1 / bit rate bitRateJ l I J Hip © McGraw Hill, LLC 20 Example 2.4 The length of the bit in Example 2.3 is 1 / 1,536,000 = 0.651 microseconds b 1536000 Ho bitrate bit BED  microsecond l53 © McGraw Hill, LLC 21 Transmission of Digital Signal 561 6 Ilija A digital signal is a composite analog signal with frequency between zero and infinity. We can have two types of transmission: baseband and broadband. The first means sending the digital signal without changing it to analog signal. The second means changing the digital signal to analog signal and send the analog signal. Eat Igf Risk110 big Ff't a basebandx v yl broadband ga Id 0 s digital Ilf WFDigital Jfk signals Digital ATTIE g signal Data  d was © McGraw Hill, LLC 22 2-2 SIGNAL IMPAIRMENT 58881 Iast Signals travel through transmission media, which are not perfect. The imperfection causes signal impairment. This means that the signal at the beginning of the medium is not the same as the signal at the end of the medium. What is sent is not what is received. Three causes of impairment are attenuation, distortion, and noise. Edit 6 s Esto Em pm attenuation 306 distortion 7 oft noises IF © McGraw Hill, LLC 23 2.2.1 Attenuation and Amplification Attenuation means a loss of energy. To compensate for this loss we 25 need amplification. When a signal, simple or composite, travels through a medium, it loses some of its energy in overcoming the resistance of the medium. To compensate for this loss, we need amplification. Figure 2.6 shows the effect of attenuation and amplification. © McGraw Hill, LLC 24 Figure 2.6 Attenuation and amplification Hi FI 642 Attenuating a Amp e s w Il Iis 656 E Oj Lamptitude His Repeateerszg.is d IIIs  Access the text alternative for slide images. © McGraw Hill, LLC 25 ofpower j 4 Amplifier WHEN 61 Example 2.5 gain of Attenuation 81 bi loss power 6ft gig Suppose a signal travels i through a transmission medium and its power is reduced to one half. This means that P2 = 0.5 P1. In this case, the attenuation (loss of power) can be calculated as H Egan images loss of powerd f A loss of 3 dB (−3 dB) is equivalent to losing one-half the power. out a log m Cyan a'Eod  dB v www.g to log ima © McGraw Hill, LLC 26 2.2.2 Distortion GIG IoT Distortion means that the signal changes its form or shape. mg Distortion can occur in a composite signal made up of different frequencies. whee phase gagging's SigingfkaJlJg Him offsite timesignals via si Isl requency nmptitud Simple 1 jg if J g s s impf Its IG distortion Isd 8 Tfs I  I © McGraw Hill, LLC 27 Gdb It wireless y Noise a I its Ig egg did9 composite is signal Noise is another cause of impairment. Several type of noise may occur during the signal transmission. frequency w m j Signal-to-Noise Ratio (SNR) is defined as SNR = (average signal power) / (average noise power)  © McGraw Hill, LLC 28 2.2.3 Data Rate Limits A very important consideration in data communications is how fast we can send data, in bits per second, over a channel. Data rate depends on three factors: Nyquist 1. The bandwidth availableq BitRateh 2.shannon Loading… The level of the signals we use 9 Bit Rate 9 3. The quality of the channel (the level of noise) noised Bitrate Two theoretical formulas were developed to calculate the data rate: one by Nyquist for a noiseless channel, another by Shannon for a  noisy channel. © McGraw Hill, LLC 29 Noiseless Channel: Nyquist Bit Rate For a noiseless channel, the Nyquist bit rate formula defines the theoretical maximum bit rate. levels job upper limit p named D od O 04 Is FIFI Bandwidth Dotty Digital © McGraw Hill, LLC 30 Example 2.6 We need to send 265 kbps over a noiseless (ideal) channel with a bandwidth of 20 kHz. How many signal levels do we need? We can use the Nyquist formula as shown: Since this result is not a power of 2, we need to either increase the number of levels or reduce the bit rate. If we have 128 levels, the  bit rate is 280 kbps. If we have 64 levels, the bit rate is 240 kbps. 27 2 128a rate 2 0 10219 Bit 1000 280 KBps Bitrate 2 20 18 1 7 7 40 © McGraw Hill, LLC 31 i Noisy Channel: Shannon Capacity For a noisy channel, we have x 9 ot signalto noiseratio WI Bandwidth BitRat's of Bitsper 4W Seconds © McGraw Hill, LLC 32 Example 2.7 Consider an extremely noisy channel in which the value of the signal-to-noise ratio is almost zero. In other words, the noise is so In strong that the signal is faint. For this channel the capacity C is calculated as shown below. This means that the capacity of this channel is zero regardless of the bandwidth. In other words, the data is so corrupted in this  channel that it is useless when received. © McGraw Hill, LLC 33 Example 2.8 We can calculate the theoretical highest bit rate of a regular telephone line. A telephone line normally has a bandwidth of 3000 Hz (300 to 3300 Hz) assigned for data communications. The signal-to-noise ratio is usually 3162. For this channel the capacity is calculated as shown below. This means that the highest bit rate for a telephone line is 34.881  kbps. If we want to send data faster than this, we can either increase the bandwidth of the line or improve the signal-to noise ratio. © McGraw Hill, LLC 34 Using Both Limits In practice, we need to use both limits. © McGraw Hill, LLC 35 Example 2.9 We have a channel with a 1-MHz bandwidth. The SNR for this channel is 63. What are the appropriate bit rate and signal level? Solution First, we use the Shannon formula to find the upper limit. BitRate upperlimitfor C a The Shannon formula gives us 6 Mbps, the upper limit. For better performance  we choose something lower, 4 Mbps, for example. Then we use the Nyquist formula to find the number of signal levels. 4 2 B FL © McGraw Hill, LLC 36 2.2.4 Performance Up to now, we have discussed the tools of transmitting data (signals) over a network and how the data behave. One important issue in networking is the performance of the network—how good is it? © McGraw Hill, LLC 37 Bandwidth 2 One characteristic that measure network performance is bandwidth. © McGraw Hill, LLC 38 Example 2.10 The bandwidth of a subscriber line is 4 kHz for voice or data. The bit rate of this line for data transmission can be up to 56 kbps, using a sophisticated modem to change the digital signal to analog. If the telephone company improves the quality of the line and O O increases the bandwidth to 8 kHz, we can send 112 kbps. ti Britate f Bandwidth do lil  2 9 Bit Rate 2 Bligh © McGraw Hill, LLC 39 Throughput Esa Bitrate The throughput is the measure of how fast we can actually send data through a network. latency f transmission E r  Y l pg Delay 19 Delay i l essing Delay Delay © McGraw Hill, LLC 40 Latency (Delay) zgion oftwHB destination A w mg The latency or delay defines how long it takes for an entire message to completely arrive at the destination from the time the first bit is sent out from the source. We say that normally have four types of delay: propagation delay, transmission delay, queuing delay, and processing delay. The latency or total delay is 915AM'T Is Aff toeamount f delay I g T I g ly Latency = propagation delay + transmission delay + queuing delay g b He get dJ6 Html P Roat + processing delay th Routers 14pm's GE o of sifpaeketdys 1 7 It E bitrate's gq T tension YI's.FIgPpyK taisaw1Fiiasislm puyg.q P 4f transmission I sonata HEY so packet's 6h404g t Ws6isI2 InIANEIlidEa.s.Eigawe.a queuingdelay Idiot Fmd is © McGraw Hill, LLC 41 bitts s Bit Bandwidth-Delay Product Biff Bandwidth and delay are two performance metric of a link. However, what is very important in data communications is the product of the two, the bandwidth-delay product. © McGraw Hill, LLC 42 Example 2.12 JEDI We can think about the link between two points as a pipe. We can say that the volume of the pipe defines the bandwidth-delay product © McGraw Hill, LLC 43 Figure 2.7 Bandwidth-delay product  0 Access the text alternative for slide images. © McGraw Hill, LLC 44 if HI IN Jitter packet Another performance issue that is related to delay is jitter. We can roughly say that jitter is a problem if different packets of data encounter different delays and the application using the data at the receiver site is time-sensitive (audio and video data, for example). If the delay for the first packet is 20 ms, for the second is 45 ms, and for the third is 40 ms, then the real-time application that uses the packets endures jitter. © McGraw Hill, LLC 45 if Ms Is sad sense us mstream eFm son 2-5 MULTIPLEXING251 F I W r deCalisto Link freq deferentRange w 6 Is Is food Data binary Analog channel Ato s s g tangyt.mg is freezing 29 streams loused In real life, we have links with limited bandwidths. Sometimes we need to combine several low-bandwidth channels to make use of one channel with a larger bandwidth. Sometimes we need to i expand the bandwidth of a channel to achieve goals such as privacy and anti-jamming. Multiplexing  fqt C 3 Is 1h pm g a if J th'llgT g 30kHz 311 1619 signal o o w qew 10k hz.fi © McGraw Hill, LLC 46 Figure 2.17 Dividing a link into channels  circuit T demultipkxing.SI Access the text alternative for slide images. © McGraw Hill, LLC 47 2.5.1 Frequency-Division Multiplexing Frequency-division multiplexing is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidth of the signals to be transmitted together. PW multiplexing a  Digital Angb9wfannawian Mlk's tremquidefein'T H I Time decision 3 channel Bandwidth T different frequency © McGraw Hill, LLC 48 Figure 2.18 Frequency-division multiplexing f DM  oh boasts d y security fig 44 frequing hopping if frequency MAH F 2 frequency Access the text alternative for slide images. © McGraw Hill, LLC 49 2.5.2 Time-Division Multiplexing digital EDM Time-division multiplexing (TDM) is a digital technique that allows several connections to share the high bandwidth of a link. © McGraw Hill, LLC 50 Figure 2.19 Time division multiplexing (TDM) e  goyim s I IT user J IF 100ms cycle B Access the text alternative for slide images. © McGraw Hill, LLC 51 2-6 TRANSMISSION MEDIA We discussed many issues related to the physical layer in this chapter. In this section, we discuss transmission media. Transmission media are located below the physical layer and are directly controlled by the physical layer. © McGraw Hill, LLC 52 Figure 2.20 Transmission media and physical layer  Binary or digita Analog Access the text alternative for slide images. © McGraw Hill, LLC 53 2.6.1 Guided Media Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and Lows fiber-optic cable. Ee ai  as unguided 7 wireless Eid Him 8 3 10 © McGraw Hill, LLC 54 Twisted-Pair Cable A twisted-pair cable consists of two conductors, each with its own plastic insulation, twisted together as shown in Figure 2.21. ssb  Itb i W © McGraw Hill, LLC 55 Figure 2.21 Twisted-pair cable j I 43 ai'S g g  unshale d if 0 If Wig W Hark so fol Attenuation 4W To _sheilted Omiya lectromagnatenic nterferance Access the text alternative for slide images. FH.mg © McGraw Hill, LLC 56 WIS Coaxial Cable Es Coaxial cable carries signals of higher frequency ranges more than those in twisted-pair cable. Coaxial cable has a central core enclosed in an insulating sheath as shown in Figure 2.22.  qa.EE f0in.nnw.ao ovffu dinEi SH 81 56W uneild © McGraw Hill, LLC 57 Figure 2.22 Coaxial cable Attenuating  wi Atty igf Ej mega HE igoimf.ge 4 e Bandwidths qjf h.IE Access the text alternative for slide images. © McGraw Hill, LLC 58 Fiber-Optic Cable A fiber-optic cable is made of glass or plastic and transmits signal in the form of light. If a light traveling in a substance enters another substance, the raysowchanges direction as shown in Figure 2.23. Figure 2.24 shows how a beam of light travels through an  optical fiber. I IT 06h most expensive SAH g't © McGraw Hill, LLC jyp 59 Figure 2.23 Bending of light ray Big  SHIFU SHIJI Ssl Ids Access the text alternative for slide images. © McGraw Hill, LLC 60 Figure 2.24 Optical fiber EHIWL.GS E  Gif I1 off If Access the text alternative for slide images. © McGraw Hill, LLC 61 2.6.2 Unguided Media: Wireless Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Signals are normally broadcast through free space and thus are available to anyone who has a  device capable of receiving them. Figure 2.25 shows part of the electromagnetic spectrum from 3KHz to 800 THz used for wireless communication. w llss.fi b © McGraw Hill, LLC 62 Figure 2.25 Electromagnetic spectrum for wireless communication it is I xi dy s GHZ 300 400 900 KHZpag.ro Tt T GHz Issy  IF HT f Access the text alternative for slide images. © McGraw Hill, LLC 63 Radio Waves miasma Although there is no clear-cut demarcation between radio waves and microwaves, electromagnetic waves ranging in frequencies between 3 kHz and 1 GHz are normally called radio waves; waves ranging in frequencies between 1 and 300 GHz are called O  microwaves. However, the behavior of the waves, rather than the frequencies, is a better criterion for classification. Radio waves, for the most part, are omnidirectional. bat 1 Microwaves Radio I digits w omnidirectional C © McGraw Hill, LLC j uaIII5gtiId o 64 Microwaves Electromagnetic waves having frequencies between 1 and 300 GHz are called microwaves. Microwaves are unidirectional. When an antenna transmits microwaves, they can be narrowly focused. This a  I means that the sending and receiving antennas need to be aligned. The unidirectional property has an obvious advantage. A pair of antennas can be aligned without interfering with another pair of aligned antennas. © McGraw Hill, LLC 65 Infrared Infrared waves, with frequencies from 300 GHz to 400 THz (wavelengths from 1 mm to 770 nm), can be used for short-range communication. Infrared waves, having high frequencies, cannot  penetrate walls. This advantageous characteristic prevents interference between one system and another; a short-range E communication system in one room cannot be affected by another system in the next room. © McGraw Hill, LLC 66 End of Main Content Because learning changes everything.® www.mheducation.com © 2022 McGraw Hill, LLC. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill, LLC.