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Computer Networking

广西医科大学. Computer Networking. 网络课件. 双语教学. 模拟实验. 计算机网络教研室. DI. 1. 2. 3. CHAPTER 7 DATA LINK CONTROL PROTOCOL. The first section. Exercises. Online lecture. Chapter 7 Data Link Control Protocol. 7.1 INTRODUCTION

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Computer Networking

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  1. 广西医科大学 ComputerNetworking 网络课件 双语教学 模拟实验 计算机网络教研室

  2. DI 1 2 3 CHAPTER 7 DATA LINK CONTROL PROTOCOL The first section Exercises Online lecture

  3. Chapter 7 Data Link Control Protocol • 7.1 INTRODUCTION • A set of rules that define the exact format of messages exchanged between computers or between computers and people is called a protocol. • Data link protocols are necessary so that all of the devices on the network are operating by the same set of rules and are able to communicate with each other. www.gxmu.edu.cn

  4. Chapter 7 Data Link Control Protocol • 7.2 DATA LINK PROTOCOLS FUNCTIONS • Communication startup • Character identification and framing • Message identification The DTE must separate the characters on the communications line into messages. www.gxmu.edu.cn

  5. Chapter 7 Data Link Control Protocol • 7.2 DATA LINK PROTOCOLS FUNCTIONS • Line Control • The part of a protocol consisting of the rules that specify the way the receiving terminal signals the sending terminal if it has received data correctly, how and under what circumstances the line will be turned around, and whether the receiving terminal can accept more data is called line control. www.gxmu.edu.cn

  6. Chapter 7 Data Link Control Protocol • 7.2 DATA LINK PROTOCOLS FUNCTIONS • Error Control The part of the protocol consisting of rules specifying what happens when an error is detected, what to do if communications suddenly and unexplainably cease, and the way communications are reestablished after they are broken is called error control. • Termination The part of a protocol consisting of rules for ending the communications under normal and abnormal circumstances is called termination. www.gxmu.edu.cn

  7. Chapter 7 Data Link Control Protocol • 7.3 DESIRABLE ATTRIBUTES OF DATA LINK PROTOCOLS • Transparency The ability of data terminal equipment (DTE) to be able to transmit and receive any bit pattern as data is called transparency . www.gxmu.edu.cn

  8. Chapter 7 Data Link Control Protocol • 7.3 DESIRABLE ATTRIBUTES OF DATA LINK PROTOCOLS • Code independence The protocol allow the transmission of data from any data coding system. • Efficiency The protocol should use as few characters as possible to control the data transmission so that most of the line capacity can be used for actual data transmission. www.gxmu.edu.cn

  9. Chapter 7 Data Link Control Protocol • 7.4 PROTOCOL IMPLEMENTION • A data link protocol is implemented by transmitting certain bit patterns or characters on the communications circuit. • 7.5 PREDETERMINED COMMUNICATIONS PARAMETERS • Predetermined communication parameters are those that are set manually by switches or specified as parameters in software. www.gxmu.edu.cn

  10. Chapter 7 Data Link Control Protocol • 7.7 LINE ACCESS • When two stations on a circuit transmit at the same time, a(n) collision occurs. • There are three primary ways that circuit access can be obtained:contention,polling,and token passing. • 7.7.1 Contention • When any station that has traffic looks to see if the circuit is free, and if it is, begins sending its traffic the line control technique is called contention. www.gxmu.edu.cn

  11. Chapter 7 Data Link Control Protocol • Contention systems work best _____. • a. on circuits that have only two DTEs • b. when the speed of the circuit is relatively fast • c. on circuits that have not too heavy message traffic • 7.7.2 Polling • When a central or control station asks each station on the circuit or network if it has traffic to send it is using a line control technique called polling. www.gxmu.edu.cn

  12. Chapter 7 Data Link Control Protocol • 7.7.2 Polling • Roll call polling • Roll call polling is the most common implementation of a polling system. • In order to know what stations to poll and in what sequence, the master station uses a polling list. www.gxmu.edu.cn

  13. Chapter 7 Data Link Control Protocol • 7.7.2 Polling • Fast select polling • Fast select polling speeds up the polling process because a slave station that doesn’t have traffic isn’t required to return a character to the master station. • Hub polling P128 7.7.3 Token passing www.gxmu.edu.cn

  14. Chapter 7 Data Link Control Protocol • 7.8 MESSAGE FORMAT • Data messages normally consist of three parts: the header, text, and trailer. • The header of a message contains and conveys information about the message, such as the destination node’s address, a sequence number, and perhaps a date and time. www.gxmu.edu.cn

  15. Chapter 7 Data Link Control Protocol Figure 7-1 Message format showing examples of the kinds of control characters the protocol might employ. www.gxmu.edu.cn

  16. Chapter 7 Data Link Control Protocol 7.9 FLOW CONTROL Techniques to ensure that a fast transmitting node does not send data faster than the receiving node can receive and process it are called flow control. 7.9.1 Stop-and-wait Flow Control Stop-and-wait Flow Control is the simplest form control. www.gxmu.edu.cn

  17. Chapter 7 Data Link Control Protocol Figure 7-2 The data flow of stop-and-wait flow control. www.gxmu.edu.cn

  18. Chapter 7 Data Link Control Protocol 7.9.2 Sliding WindowFlow Control The flow control technique that allows multiple frames to be in transit on the line at one time is called sliding window. There are two common implementations of sliding window flow control:go-back-n and selective repeat. www.gxmu.edu.cn

  19. Chapter 7 Data Link Control Protocol Figure 7-3 The data flow in a simple sliding window flow control. www.gxmu.edu.cn

  20. Chapter 7 Data Link Control Protocol 7.10 ASYNCHRONOUS DATA LINK PROTOCOLS Asynchronous data link protocols deal with individual characters rather than blocks of data. 7.10.1 Point-to-Point Protocol(PPP) A protocol that is primarily used by PC workstations to send IP over dial-up lines, typically when dialing in to an ISP for connection to the Internet, is called PPP. PPP has largely replaced the SLIP protocol because it has better error detection. www.gxmu.edu.cn

  21. Chapter 7 Data Link Control Protocol Figure 7-4 PPP’s frame format. www.gxmu.edu.cn

  22. Chapter 7 Data Link Control Protocol 7.10.2 XMODEM Protocol The XMODEM protocol was developed for use between PCs, especially for transfers of data files between them. 7.10.3 Other Asynchronous Protocols A sophisticated check character at the end of each block of data is called a cyclic redundancy check(CRC). www.gxmu.edu.cn

  23. Chapter 7 Data Link Control Protocol 7.11 SYNCHRONOUS DATA LINK PROTOCOLS • Synchronous data link protocols typically deal with blocks of data,not individual characters. • The three types are character-oriented protocol,byte-count-oriented protocol,and bit-oriented protocols. www.gxmu.edu.cn

  24. Chapter 7 Data Link Control Protocol 7.11.1 Character-Oriented Protocols • A character-oriented protocol uses special characters to indicate the beginnings and ends of messages. • The best known character-oriented protocol is the Binary Synchronous Communications Protocol(BSC),also known as BISYNC. • BISYNC is defined to only support the 6-bit transcode (SBT), EBCDIC, and ASCII. www.gxmu.edu.cn

  25. Chapter 7 Data Link Control Protocol 7.11.2 Byte-Count-Oriented Protocols • Byte-count-oriented protocols have a special characters to mark the beginning of the header,followed by a count field that indicates how many characters are in the data portion of the messages. • The best known byte-count-oriented protocol is the Digital Data Communications Message Protocol(DDCMP). www.gxmu.edu.cn

  26. Chapter 7 Data Link Control Protocol 7.11.3 Bit-Oriented Protocols • A bit-oriented protocol uses only one special character,called the flag character,which marks the beginning and end of parts of the message. • The best known bit-oriented protocols are the ISO’s High-Level Data Link Control (HDLC) protocol. • SDLC is a subset of HDLC. • 7.12 OTHER DATA LINK PROTOCOLSP143 www.gxmu.edu.cn

  27. Chapter 7 Data Link Control Protocol • 7.13 PROTOCOL CONVERSION • A protocol converter changes one protocol to another, when, for example, a message is sent between two networks that use different protocols. www.gxmu.edu.cn

  28. Chapter 7 Data Link Control Protocol 课后习题 1.When an HDLC node receives a flag character, it knows that （　　）. C × A、 an error has occurred × B、 it should signal the sender to stop sending traffic C、 a frame is beginning or ending √ × D、 it should switch to transparent mode Redo Next Answer

  29. Chapter 7 Data Link Control Protocol 课后习题 2.When two stations on a circuit transmit at the same time, a(n) （　　）occurs. D × A、 division × B、 polling × C、 bit stuffing D、 collision √ Redo Next Answer

  30. Chapter 7 Data Link Control Protocol 课后习题 3.In order to know what stations to poll and in what sequence, the master station uses a （　　）. B A、 message header × B、 polling list √ × C、 start of header character × D、 cyclic redundancy check Redo Next Answer

  31. Chapter 7 Data Link Control Protocol 课后习题 4. Go-back-n and selective repeat are two common implementations of （　　）. D × A、 bit oriented protocols × B、 byte protocols × C、 byte-count oriented protocols D、 sliding window flow control √ Redo Next Answer

  32. Chapter 7 Data Link Control Protocol 课后习题 5. When a receiver must acknowledge every block of data before the next block is sent, the （　　） type of flow control is being used. A A、 stop-and-wait √ B、 stop-and-check × C、 sliding frame × × D、 sliding window Redo Next Answer

  33. Chapter 7 Data Link Control Protocol 课后习题 • HDLC 6.SDLC is a subset of ________. Answer 7.BISYNC is defined to only support the 6-bit transcode (SBT), EBCDIC, and _________ . ASCII Answer 8.A set of rules that define the exact format of messages exchanged between computers or between computers and people is called a ______________ . protocol Answer

  34. Chapter 7 Data Link Control Protocol 课后习题 9.A technique used to ensure that a fast transmitting node does not send data faster than a receiving node can receive and process it is called ___________ . flow control Answer 10.A protocol that is primarily used by PC workstations to send IP over dial-up lines, typically when dialing in to an ISP for connection to the Internet, is called _____. PPP Answer

  35. Chapter 7 Data Link Control Protocol Thank You ! www.gxmu.edu.cn

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