1Fundamentals of Data & SignalsSchool of BusinessEastern Illinois University © Abdou Illia, Fall 2014(September 29, 2014)2Learning Objectives Distinguish between Data and Signals Understand transmission speed Distinguish between Bit Rate and Baud Rate3Data and Signals Ingredients of computer networks– Computers– Transmission media– Hubs/Switches– Routers, bridges– Etc. Other ingredients– Software– Data– Signals24Data Data = Entities that convey meaning within a computer system Examples of data (captured and stored on storage devices)– Files on a hard drive– Movie on a DVD– Music on a CD For transmission, Data (static entities) need to be converted into signals (dynamic entities)5Signals Signal = Electric or electromagnetic encoding of data for transmission– Using a physical transmission medium– Using airwaves Examples of signals (situations)– Telephone conversation over a telephone line– Live television news interview from Europe– Web page download over your telephone line via the Internet6Data and Signals Both Data (sources of data) and Signals can be– either analog– or digital Four combinations– Transmitting digital data using digital signals– Transmitting digital data using analog signals– Transmitting analog data using analog signals– Transmitting analog data using digital signals Need Translation devices37Translation Devices Source of Data versus LineAnalog Line Digital LineAnalog Device (e.g. Tel)CodecDigital Device (e.g. Computer)Modem DSUTranslatorTransmission LineSource of Data8DSU (Data Service Unit) DSU translates between different digital formats– Device and line are both digital, but still might need translator because Different bit rates Different number of possible states Different voltage levels for the states Different ways to represent ones and zeros9Analog signals Represented as continuous waveforms In analog transmission, the state of the signal (voltage level, etc.) varies continuously and smoothly among an infinite number of states– States could be signal strength, voltage level, or other measurable conditions410Digital signals Represented as discrete (non-continuous) waveform In digital transmission, time is divided into periods of fixed length called clock cycles The state of the signal (voltage level, etc.) remain constant during each clock cycle.– Typically, there are between two and 64 possible states.– Here, only two states are shownClock CycleTimeVoltage11Digital Signals At the end of each clock cycle, the state maychange abruptly to another of the few possible states– Can also stay the sameClock CycleTimeAbruptChangeStays SameVoltage12Digital Versus Binary Transmission Digital transmission: a few states Binary transmission: exactly two states (1 and 0)– Binary is a special case of digitalDigital BinaryTwo StatesFew States01513States and Bits 2Bits per clock cycle=Number of states– For 1 bit per clock cycle,– 2 states are required (One for 1, one for 0)– 21=2– Binary100001Clock CycleStates14States and Bits 2Bits/clock cycle=States– For 2 bits per clock cycle, 4 states are required (22=4)– For 3 bits per clock cycle, 8 states are needed (23=8)– For 4 bits per clock cycle, 16 states are needed (24=16)3 (11)2 (10)1 (01)0 (00)00011011Clock CycleStates15States and Bits 2Bits per clock cycle=States– With 4 states, send two bits per clock cycle (22=4)– With 8 states, send 3 bits per clock cycle (23=8)– With 16 states, send 4 bits per clock cycle (24=16)3 (11)2 (10)1 (01)0 (00)00011011Clock CycleStates616Bits 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 Made17Equations # 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)18ExerciseA) 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?719Summary Questions1. Distinguish between digital and analog signals2. Distinguish between digital and binary transmission3. What is the difference between the bit rate and the baud rate?
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