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Introduction to Information Technologies
Fall 2004 Lektion 4 Forts kapitel 4: Digital transmission. History of Internet
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Introduction to Information Technologies
Fall 2004 Chapter 4 Digital Baseband Transmission Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure DC component Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Lack of synchronization Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Example 3 In a digital transmission, the receiver clock is 0.1 percent faster than the sender clock. How many extra bits per second does the receiver receive if the data rate is 1 Kbps? How many if the data rate is 1 Mbps? Solution At 1 Kbps: 1000 bits sent 1001 bits received1 extra bps At 1 Mbps: 1,000,000 bits sent 1,001,000 bits received1000 extra bps Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Lack of synchronization Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Example 3 In a digital transmission, the receiver clock is 0.1 percent faster than the sender clock. How many extra bits per second does the receiver receive if the data rate is 1 Kbps? How many if the data rate is 1 Mbps? Solution At 1 Kbps: 1000 bits sent 1001 bits received1 extra bps At 1 Mbps: 1,000,000 bits sent 1,001,000 bits received1000 extra bps Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Line coding schemes Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Note: Unipolar encoding uses only one voltage level. Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Unipolar encoding Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Note: Polar encoding uses two voltage levels (positive and negative). Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Types of polar encoding Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Note: In NRZ-L the level of the signal is dependent upon the state of the bit. Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Note: In NRZ-I the signal is inverted if a 1 is encountered. Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure NRZ-L and NRZ-I encoding Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure RZ encoding Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Note: A good encoded digital signal must contain a provision for synchronization. Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Manchester encoding Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Note: In Manchester encoding, the transition at the middle of the bit is used for both synchronization and bit representation. Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Differential Manchester encoding Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Note: In differential Manchester encoding, the transition at the middle of the bit is used only for synchronization. The bit representation is defined by the inversion or noninversion at the beginning of the bit. Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Note: In bipolar encoding, we use three levels: positive, zero, and negative. Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Bipolar AMI encoding Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Mulilevel pulse amplitude modulation (PAM) Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Mulilevel PAM A signal has M data levels with a pulse duration of T PulseRate fs = 1 / T pulses/s Bit Rate R = fs x log2 M Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Example A signal has four data levels with a pulse duration of 1 ms. We calculate the pulse rate and bit rate as follows: Pulse Rate = = 1000 pulses/s Bit Rate = PulseRate x log2 L = 1000 x log2 4 = 2000 bps Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Data transmission and modes Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Parallel transmission Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Serial transmission Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Note In asynchronous transmission, we send 1 start bit (0) at the beginning and 1 or more stop bits (1s) at the end of each byte. There may be a gap between each byte. Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Note Asynchronous here means “asynchronous at the byte level,” but the bits are still synchronized; their durations are the same. Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Asynchronous transmission Computer Networks History of Internet
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Exempel på asynkron serie-kommunikation: RS232C (”com-porten”)
Introduction to Information Technologies Fall 2004 Exempel på asynkron serie-kommunikation: RS232C (”com-porten”) Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Note In synchronous transmission, we send bits one after another without start or stop bits or gaps. It is the responsibility of the receiver to group the bits. Computer Networks History of Internet
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Introduction to Information Technologies
Fall 2004 Figure Synchronous transmission Computer Networks History of Internet
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