1Review For Exam 2School of BusinessEastern Illinois University © Abdou Illia, Spring 2010March 9, 2010Fundamentals of Data & SignalsSchool of BusinessEastern Illinois University 3Summary Questions1. Distinguish between digital and analog signals in relation to noise.Answer: Digital signals are represented as discrete (i.e. non continuous) waveform, whereas digital signals are represented as continuous waveforms.2. Distinguish between digital and binary transmissionAnswer: In digital transmission, the state of the signal varies from 2 to 64 sates.. In binary transmission, there are exactly two states.3. What is the difference between the bit rate and the baud rate? Answer: see next slide.9-101216in Fundamentals of Data & Signals Notes24Bits and Baud Baud Rate = Number of clock cycles/sec– In this example, 4 baud (not 4 bauds/second)– Note: Number of clock cycles, not actual line changes Bit Rate = Number of bits/second– In this example, 8 bits/second Bit Rate = Baud Rate * Bits per clock cycle000110011 SecondPossible Change Not Made5Equations # of states– 2Bits per clock cycle= Number of possible states (Eq. 1) Bit rate– Bit rate = Baud Rate * Bits per clock cycle (Eq. 2) Exercise(See next slide)6ExerciseA) If a transmission line has a Baud rate of 10 000 baud, and if there are eight possible line states, what is the Bit rate? B) If you wish to send two bits per clock cycle, how many possible states must you have?37Translation Devices Source of Data versus LineAnalog Line Digital LineAnalog Device (e.g. Tel)CodecDigital Device (e.g. Computer)Modem DSUTranslatorTransmission LineSource of DataFundamentals of Data & Signals (Part 2)School of BusinessEastern Illinois University 9AttenuationOverall gain or loss = -10 dB + 20dB - 15dB = -5dB Attenuation = Loss of Signal Strength Function of Distance and Friction within the Medium If high signals get too weak, the receiver will not be able to detected it.  Decibel (dB) is a relative measure of signal loss or gain of strength. dB = 10 log10(P2 / P1), Where P2 & P1 are ending and beginning power levels (in watt)(Figure 2-10 in textbook)410Attenuation A signal starts at a transmitter with 10 watts of power and arrived at a receiver with 5 watts of power. Calculate the loss of power in dB.1. dB = 10 log10(P2 / P1) 2. dB = 10 log10(5/10)3. dB = 10 log10(0.5)4. dB = 10 (-0.3)5. dB = -3Q: What is the decibel loss of a signal that starts at 50 watts and experiences a 10-watt loss over a given section of cable ?Q:What is the decibel loss of a signal that loses half its power during the course of transmission ?11Summary Questions1. What is the main advantage of digital signals over analog signals in regards to noise?Answer: It’s easier to remove noise from digital signals (Slide #4 in Fundamentals of Data & Signals -continued)2. What are the three main characteristics of signals ? Answer: Amplitude, Frequency and Phase3. What is the bandwidth of a signal ? The spectrum?Bandwidth=absolute value of the difference between the maximum and the minimum frequenciesSpectrum=Range of frequencies from minimum to maximum4. (a) Name one technique for converting digital data into digital signals. (b) Name 3 techniques for converting digital data into analog signals4a) NRZ-L or Differential Manchester. 4b) Amplitude modulation, Frequency modulation, Phase modulationConducted MediaSchool of BusinessEastern Illinois University513Summary Questions What does cross talk interference mean ? How can crosstalk interference be reduced ?If transmission wires are placed side by side, electromagnetic radiation is emitted by one wire and picked up by the other. Twisting pair of wire reduce crosstalk interference. What categories of twisted pair are usually used in LANs ?Categories 3, 4, 5, 6, 7, 8 What are the advantages and disadvantages of STP compared to UTP ?Advantage: better level of isolation from interference. Disadvantage: cost What is the main difference between Baseband coaxial cable and Broadband coaxial cable ?Baseband transmit digital signal in a single channel, whereas broadband uses multiple channels to transmit digital or analog signals. What are the advantages of Optical fiber compared twisted pair and coaxial cable ?Speed, No significant noise, No interference, Long distance Can you transmit video signal over twisted pair wire ? ExplainYes, you can (e.g. Digital Video Service or DVS). Noise used to be a limitating factor.14Case study The following figure shows a common situation in LANs. Remember : – Using Category 5 UTP, the maximum segment length is 100 meters.– A wall jack is a passive device and does not regenerate a signalCat 5-UTPCrossover cable15Case studyCat 5-UTPCrossover cable What kind of problem there will be if the distance between the Workstation and the Hub is more than 100 meters? What solution can be applied ? If the cable that connects the workstation and the hub passes through a noisy environment (Heating or cooling mechanical room) what action could be taken to prevent interference?616Case studyCat 5-UTPCrossover cable If the needed data rate is higher than 100 Mbps, what are the possible solutions?Wireless MediaSchool of BusinessEastern Illinois University 18Wireless Media Use electromagnetic waves or electromagnetic radiation for data transmission Propagation through space, and indirectly, through solid objects Many problems:LaptopComm. TowerShadowZoneRadio waves tend to bounce off objects. Receiver can receive 2 or more signals.Thick objects can block the direct path. So, Receiver will be in a Shadow zone where it cannot well receive.Insecure: Easier to “intercept”messagesElectromagneticInterference (EMI) from Other stations,Microwave ovens, etcMultipathInterference+ Much more attenuation: Inverse Square law719Wireless LAN (802.11 standard)SwitchClient PCServerWired LANAccessPoint AAccessPoint BUTPRadio wavesHandoffIf mobile computermoves to anotheraccess point,it switches serviceto that access pointLaptopMAC protocol: CSMA/CA+ACK802.11 Frame802.3 Frame Typical physical typology: Point-to-Multipoint20Summary Questions a) Wireless transmission can experience propagation problems due to shadow zones and multipath interference. Explain. b) What does handoff refer to? c) Explain how attenuation occurs in wireless communications: Inverse square law.Local Area NetworksSchool of BusinessEastern Illinois