1. 1 Introduction 4 Information transfer between two computers occurs in one of two types signals: digital or analog. Chapter 2 Introduction to Data Communication

2. 2 2.5 Transmission Modes 4 When data is transferred, the receiving computer must determine when one signal ends and when the next one begins 4 Two types: Asynchronous transmission and Synchronous transmission. Chapter 2 Introduction to Data Communication

3. 3 AsynchronousAsynchronous transmissiontransmission AsynchronousAsynchronous transmissiontransmission 4 adds a start bit, one or two end bits and a parity bit (for error detection) to achieve synchronizationparity 4 Occurs character by character and used for serial communication, such as by modem. 2.5 Transmission Modes

4. 4 SynchronousSynchronous transmissiontransmission SynchronousSynchronous transmissiontransmission 4 use a clock pulse for synchronization 4 Transfer large blocks of data and used for parallel transmission, such as reading a file or printing information. 2.5 Transmission Modes

5. 5 2.6 Transmission Methods 4 Serial communication is a method by which data is transmitted one bit at a time over a single transmission media 4 Parallel transmission is a method by which data is transmitted byte by byte (eight bits). Chapter 2 Introduction to Data Communication

6. 6 2.7 Communication Modes 4 Simplex Mode ： one direction only 4 Half-Duplex Mode ： two devices exchange information in only one direction at a time 4 Full-Duplex Mode ： both computers can send and receive information simultaneously. Chapter 2 Introduction to Data Communication

7. 7 2.8 Bandwidth and Signal Transmission 4 bandwidth in communication is the range of frequencies that signal occupies. Chapter 2 Introduction to Data Communication

8. 8 Signal transmission 4 Baseband mode uses the bandwidth of a transmission media to carry only one signal (Use digital signals) 4 Broadband mode uses the bandwidth of a transmission media to carry several signals (Use analog signals). 2.8 Bandwidth and Signal Transmission

9. 9 2.9 Digital signal encoding 4 Digital information can be represented by several forms of digital signal, such as NRZ (WAN), NRZ-I, Manchester and Differential Manchester (LAN). Chapter 2 Introduction to Data Communication

10. 10 Encoding and Modulation 4 Analog Signal 4 Modulation : AM 、 FM 、 PM 4 Encoding ： PCM 4 Digital Signal 4 Encoding ： NRZ 、 Manchester 4 Modulation ： ASK 、 FSK 、 PSK. 2.9 Digital signal encoding

11. 11 Manchester Encoding 4 The clock pulse is embedded into the signal 4 Manchester Encoding ： 4 One bit is divided into two parts, the first part is not changed, the second part is changed(0->1,1->0). 2.9 Digital signal encoding

12. 12 Manchester Encoding 2.9 Digital signal encoding

13. 13 Manchester Differential Encoding 4 The first bit is the same as Manchester Encoding 4 From the second bit: 4 1->the first part is the same as the second part of previous;0-> the first part is opposite to the second part of previous 4 the second part is opposite to the first part. 2.9 Digital signal encoding

14. 14 Manchester Differential Encoding 2.9 Digital signal encoding

15. 15 2.10 Error detection methods 4 When the transmitter sends a frame to the receiver, the receiver must first check it. Chapter 2 Introduction to Data Communication

16. 16 Methods to detect error 4 Parity Check 4 BCC 4 One’s complement of sum (checksum) 4 CRC. 2.10 Error detection methods

17. 17 Parity Check 4 Simplest error detection method 4 Can detect one error 4 Before transmitting to the receiver, a parity bit (an extra bit) adds to the information 4 The receiver checks it. 2.10 Error detection methods

18. 18 Even Parity 4 1000011 ： parity bit is 1 4 0101101 ： parity bit is 0 4 Used in serial communication, limited to detection only one error and is used for transmitting single characters. 2.10 Error detection methods

19. 19 Block Check Character 4 When a block of characters is transmitted, BCC can be used to detect two errors 4 BCC uses vertical and horizontal parity bits in order to detect double errors. 2.10 Error detection methods

20. 20 TABLE 2.6

21. 21 One’s Complement of the Sum 4 Used for error detection of TCP header and IP header 4 Disadvantage ： 2.10 Error detection methods 00010011 00100000 00110001 000100110111

22. 22 Cyclic Redundancy Check 4 If frame M = 10010110 (K=8 bits) M(X)=X 7 +X 4 +X 2 +X （ K-1=7 ） 4 If divisor P =1010101 (N+1 bits) P(X)=X 6 +X 4 +X 2 +1 （ N=6) 4 Modulo-2 addition to calculate FCS ： 2 n *M= X 6 M = X 13 +X 10 +X 8 + X 7 （ 10010110000000 ）. 2.10 Error detection methods

23. 23 FCS 4 FCS= 2 n *M/P= X 3 +X 2 +X+1 4 0-1=1 4 1-0=1 4 0-0=0 4 1-1=0 CRC 10110011 1010101|10010110000000 1010101 1111000 1010101 1011010 1010101 1111000 1010101 1011010 1010101 FCS----1111

24. 24 The transmit frame 4 Transmit frame T = 2 n *M+FCS ： 4 2 n *M= X 13 +X 10 +X 8 + X 7 4 FCS= 2 n *M/P= X 3 +X 2 +X+1 4 T(X)=X 13 +X 10 +X 8 +X 7 + X 3 +X 2 +X+1 10010110001111. CRC

25. 25 Check 4 Divides T by P using modulo-2 division, if FCS=0, no error CRC 10110011 1010101|10010110001111 1010101 1111000 1010101 1011010 1010101 1111111 1010101 0

26. 26 P(X) 4 IEEE and ITU standards: 4 CRC 12 =X 12 +X 11 +X 3 +X 2 +1 4 CRC 16 =X 16 +X 15 +X 2 +1 4 CRC-ITU =X 16 +X 12 +X 5 +1 4 CRC 32 =X 32 +X 26 +X 23 +X 22 + X 16 +X 11 +X 10 +X 8 + X 7 +X 5 +X 4 +X 2 +X +1. CRC

27. 27 Short answer questions 4 27, 28, 31, 33 4 36, and the transmits frame T Chapter 2 Introduction to Data Communication