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CHAPTER 1 INTRODUCTION Access to computers and the Internet has become a basic need for education in our society. Kent Conrad (US Senator) CHAPTER 1: INTRODUCTION 2 Chapter 1: Introduction 3 CHAPTER 1: INTRODUCTION 4 CHAPTER 1: INTRODUCTION 這個世界原本屬於一群高喊知識就是力量、重 視理性分析的特定族群──會寫程式的電腦工 程師,專搞訴狀的律師,和玩弄數字的MBA。 如今,世界將屬於具有高感性能力的另一族群 ──有創造力、具同理心、能觀察趨勢,以及 為事物賦予意義的人。 我們正從一個講求邏輯、循序性與計算機效能 的資訊時代,轉化為一個重視創新、同理心, 與整合力的感性時代。 5 CHAPTER 1: INTRODUCTION 六種攸關最近的未來有無前途的關鍵性能力 一、不只有功能,還重設計。 光是提供堪用的產品、服務、體驗或生活型態,已經不 夠了。如今無論為賺錢或為成就感,都必須創作出好看、 獨特,或令人感動的東西。 二、不只有論點,還說故事。 現代人面對過量資訊,一昧據理力爭是不夠的。總有人 會找到相反例證來反駁你的說法。想要說服別人、灌輸 資訊,甚至說服自己,都必須具備編織故事的能力。 6 CHAPTER 1: INTRODUCTION 六種攸關最近的未來有無前途的關鍵性能力 三、 不只談專業,還須整合。 工業時代和資訊時代需要專業和專才,但隨著白領工作 或被外包出去,或被軟體取代,與專業相反的才能也開 始受到重視:也就是化零為整的整合能力。今日社會最 需要的不是分析而是綜合──綜觀大趨勢、跨越藩籬、 結合獨立元素成為新好產品的能力。 四、不只講邏輯,還給關懷。 邏輯思考是人類專屬能力之一。不過在一個資訊爆炸、 分析工具日新月異的世界裡,光靠邏輯是不行的。想在 未來繼續生存,必須了解他人的喜好需求、建立關係, 並展現同理心。 7 CHAPTER 1: INTRODUCTION 六種攸關最近的未來有無前途的關鍵性能力 五、不只能正經,還會玩樂。 太多證據顯示多笑、保持愉悅心情、玩遊戲和幽默感, 對健康與工作都有極大好處。當然該嚴肅的時候要嚴肅, 不過太過正經對事業不見得有益,對健康更有害。在感 性時代,無論工作還是居家,都需要玩樂。 六、 不只顧賺錢,還重意義。 我們生活在一個物質極為充裕的世界。無數人因此掙脫 了營生桎梏,得以追求更深層的渴望:生命目的、出世 意義,以及性靈滿足。 8 CHAPTER 1: INTRODUCTION 這六種關鍵能力來自兩種感知:高感性(High Concept)與高體會(High Touch) 高感性,指的是觀察趨勢和機會,以創造優美或 感動人心的作品,編織引人入勝的故事,以及結 合看似不相干的概念,轉化為新事物的能力。 高體會,則是體察他人情感,熟悉人與人微妙互 動,懂得為自己與他人尋找喜樂,以及在繁瑣俗 務間發掘意義與目的的能力。 9 CHAPTER 1: INTRODUCTION Why is all this happening? Because of the Internet! 10 Chapter 1: Introduction Computer Networks Users make the decision. vs. Distributed Systems O.S. makes the decision. 11 Chapter 1: Introduction Middleware: The software layer that lies between the operating system and applications on a distributed computing system in a network. Middleware services provide a more functional set of application programming interfaces to allow an application to: 1. Locate transparently across the network, thus providing interaction with another service or application 2. Be independent from network services 3. Be reliable and available always when compared to the operating system and network services. 12 CHAPTER 1: INTRODUCTION A well-known example of a distributed system is the World Wide Web. It runs of top of the Internet and presents a model in which everything looks like a document (Web page). In a computer network, this coherence, model, and software are absent. 13 Chapter 1: Introduction 1.1 Uses of Computer Networks 1.1.1 Business Applications Goals: •Resource Sharing •High Reliability •Saving Money •Communication Medium (people to people, machine to machine) 14 Chapter 1: Introduction 1.1 Uses of Computer Networks 1.1.1 Business Applications Client-server model A network with two clients and one server. 15 Chapter 1: Introduction 1.1 Uses of Computer Networks 1.1.1 Business Applications The client-server model involves requests and replies. 16 Chapter 1: Introduction 1.1 Uses of Computer Networks 1.1.1 Business Applications Client-server model server type Concurrent server vs. Iterative server Stateful server vs. Stateless server Examples: 17 Chapter 1: Introduction 1.1 Uses of Computer Networks 1.1.2 Home Applications •Access to remote information World Wide Web •Person-to-person communication Electronic mail, IM, Videoconference •Interactive entertainment Video-on-Demand, Games •Electronic commerce •Social networks 18 Chapter 1: Introduction 1.1 Uses of Computer Networks 1.1.2 Home Applications In peer-to-peer system there are no fixed clients and servers. 19 CHAPTER 1: INTRODUCTION BitTorrent Instant Messaging Twitter Facebook, Google+ Wikipedia 20 Chapter 1: Introduction 1.1 Uses of Computer Networks 1.1.2 Home Applications Some forms of e-commerce. 21 CHAPTER 1: INTRODUCTION IPTV Ubiquitous Computing Sensor networks Power-line networks RFID (Radio Frequency Identification) 22 Chapter 1: Introduction 1.1 Uses of Computer Networks 1.1.3 Mobile Users Combinations of wireless networks and mobile computing. 23 CHAPTER 1: INTRODUCTION Wi-Fi (Wireless Fidelity) (from Hi-Fi) (IEEE 802.11 standard) Hopspots Mobile phones SMS, MMS (Short Message Service, Multimedia MS) Texting, Intexicated, Sexting, Smart phones 24 CHAPTER 1: INTRODUCTION GPS (Global Positioning System) Location-based services (can you give some examples?) M-commerce (mobile-commerce) RFID (Radio Frequency Identification) again NFC (Near Field Communication) Wearable Computers 25 CHAPTER 1: INTRODUCTION Social Issues Network Neutrality DMCA (Digital Millennium Copyright Act), DRM (Digital Rights Management) Profiling and cookies Botnet (DDoS) Phishing CAPTCHA 26 Chapter 1: Introduction 1.1 Uses of Computer Networks 1.1.4 Social Issues Privacy Copyright Pornography Anonymity Security Worms and Virus freedom of speech vs. censorship responsibility of the service providers … 27 Chapter 1: Introduction 1.2 Network Hardware Broadcast Networks shared link (may be wireless) 28 Chapter 1: Introduction 1.2 Network Hardware Point-to-point Networks point to point link 29 CHAPTER 1: INTRODUCTION Packet Unicast, Multicast, Broadcast PAN, LAN, MAN, WAN Interplanetary Internet 30 Chapter 1: Introduction 1.2 Network Hardware Classifying by scales Classification of interconnected processors by scale. 31 CHAPTER 1: INTRODUCTION Personal Area Networks Bluetooth RFID Bluetooth PAN configuration 32 Chapter 1: Introduction 1.2 Network Hardware Local Area Networks IEEE的定義: A LAN (Local Area Network) is a data communication system allowing a number of independent devices to communicate directly with each other, within a moderately sized geographic area over a physical communication channel of moderate data rates. 33 Chapter 1: Introduction 1.2 Network Hardware Local Area Networks LAN: •short geographical distance (a few kilometers) •high speed (Larger than 10 Mbps) •multiple access (Many can use it at the same time) •sharing (hardware, software, idea, feeling, emotion...) 34 Chapter 1: Introduction 1.2 Network Hardware Local Area Networks Ethernet Token Ring Two broadcast networks (a) Bus Wireless and wired LANs. (a) (b) Ring 802.11. (b) Switched Ethernet 35 Chapter 1: Introduction 1.2 Network Hardware Local Area Networks Standardization Body IEEE (Institute of Electric and Electronic Engineers) 802 group For example: 802.3: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) (Ethernet is one of them.) 802.11: Wireless LANs (Wi-Fi: Wireless Fidelity) 36 CHAPTER 1: INTRODUCTION Home network The networked devices have to be very easy to install The network and devices have to be foolproof in operation Low price is essential for success It must be possible to start out with one or two devices and expand the reach of network gradually (no format wars) Security and reliability will be very important 37 CHAPTER 1: INTRODUCTION Virtual LAN 38 Chapter 1: Introduction 1.2 Network Hardware Metropolitan Area Networks A metropolitan area network based on cable TV. 39 CHAPTER 1: INTRODUCTION Wireless MAN 3G->4G WiMax (Worldwide Interoperability for Microwave Access) LTE (Long Term Evolution) 40 CHAPTER 1: INTRODUCTION WAN using a virtual private network WAN using an three ISP network WANWAN that connects branch offices in Australia 41 Chapter 1: Introduction 1.2 Network Hardware Wide Area Networks Relation between hosts on LANs and the subnet. 42 Chapter 1: Introduction 1.2 Network Hardware Wide Area Networks A stream of packets from sender to receiver. 43 Chapter 1: Introduction 1.2 Network Hardware Wide Area Networks store-and-forward network B A A sends a message to C through B. C B must store this message until B is sure that C has received it. Store first, then forward. But when to start forwarding? 44 Chapter 1: Introduction 1.2 Network Hardware Wide Area Networks store-and-forward network B A A sends a message to C through B. C When to starting forwarding? 1. After the message is completely received 2. Start forwarding after a fixed amount of information(bits) received 3. Start forwarding immediately after receiving data (cut-through) 45 Chapter 1: Introduction 1.2 Network Hardware Wide Area Networks store-and-forward network B A A sends a message to C through B. C If a message takes 1 minute to travel a link: A B C 0 m1 0.25 m2 m1 0.5 m3 m2 m1 0.75 m4 m3 m2 1.0 m4 m3 1.25 m4 (1) A to B, then B to A: 2 minutes (2) message is decomposed into 4 parts: 1.25 minutes (each part is called a packet) 46 Chapter 1: Introduction 1.2 Network Hardware Wide Area Networks The concept of pipelining If the message is decomposed into N packets, each packet takes 1/N minutes to travel a link. It takes 2 N 1 minutes. N N 但分的愈細愈好嗎? bits h header t user information trailer overhead for N packets=N(h+t) overhead for 1 message=h+t 47 Chapter 1: Introduction 1.2 Network Hardware Wide Area Networks B Switching D G A E H C F (1) circuit switching (in telephone) (2) packet switching (3) message switching Wide Area Networks: Dod: ARPANET in 1960s (become Internet) IBM: SNA in 1974 DEC: DECNET in 1975 CCITT X.25 in 1970s Current Internet practice: store-and-forward packet switching 48 Chapter 1: Introduction 1.2 Network Hardware Wide Area Networks Switching Bottleneck in current store-and-forward packet switching network: ROUTING router packets delayed (or even discarded) in routers 49 Chapter 1: Introduction 1.2 Network Hardware Wireless Networks The fast-growing segment of the industry: •notebook computers •personal digital assistants •cellular phones Before long, we would have: •palmtop computers •wristwatch computers •… 50 Chapter 1: Introduction 1.2 Network Hardware Wireless Networks Categories of wireless networks: 1. (used for) System interconnection 2. Wireless LANs 3. Wireless WANs 51 Chapter 1: Introduction 1.2 Network Hardware Wireless Networks (a) Bluetooth configuration (b) Wireless LAN 52 Chapter 1: Introduction 1.2 Network Hardware Wireless Networks (b) is more efficient and economical. NEMO: NEtwork MObility 53 Chapter 1: Introduction 1.2 Network Hardware Home Networks 1. 2. 3. 4. 5. Computers (desktop PC, PDA, shared peripherals Entertainment (TV, DVD, VCR, camera, stereo, MP3) Telecomm (telephone, cell phone, intercom, fax) Appliances (microwave, fridge, clock, furnace, airco, lights) Telemetry (utility meter, smoke/burglar alarm, thermostat, babycam). 54 Chapter 1: Introduction 1.2 Network Hardware Internetworks Networking is a world wide phenomenon. NII: National Information Infrastructure -> GII (Global II) Information Superhighway Internet Internet II Next Generation Internet 55 Internet Usage 56 Chapter 1: Introduction 1.3 Network Software 1. 2. 3. 4. 5. Protocol Hierarchies Design Issues for the Layers Connection-Oriented and Connectionless Services Service Primitives The Relationship of Services to Protocols 57 Chapter 1: Introduction 1.3 Network Software peers 1.3.1 Protocol Hierarchies 58 Chapter 1: Introduction 1.3 Network Software 1.3.1 Protocol Hierarchies A set of layers and protocols is called a network architecture. A list of protocols used by a certain system, one protocol per layer, is called a protocol stack. 59 An analogy French The common Dutch can be replaced with another. Email can be used instead of fax. 60 Chapter 1: Introduction 1.3 Network Software Example information flow supporting virtual communication in layer 5 61 Chapter 1: Introduction 1.3 Network Software Relations between layers at an interface 62 Chapter 1: Introduction 1.3 Network Software 1.3.2 Design Issues for the Layers •A mechanism for identifying senders and receivers (naming and addressing) •rules of transfer (simplex, half-duplex, full-duplex) •error control (error correction and error detection) •ordering and sequencing •flow control, congestion control, quality of service •message or packet size (disassembling and reassembling) •multiplexing and demultiplexing •Routing, scalability •Security (confidentiality, authentication, integrity) 63 Chapter 1: Introduction 1.3 Network Software 1.3.3 Connection-Oriented and Connectionless Services Six different types of service 64 Chapter 1: Introduction 1.3 Network Software 1.3.3 Connection-Oriented and Connectionless Services Issue Initial Destination Packet Error Flow Option setup address sequence control control negotiation only needed by by guaranteed during setup network network layer layer Connection Oriented required Connectionless needed for by by not not possible every packet guaranteed transport transport layer layer Yes No 65 Chapter 1: Introduction 1.3 Network Software 1.3.4 Service Primitives Five service primitives for implementing a simple connection-oriented service 66 Chapter 1: Introduction 1.3 Network Software 1.3.4 Service Primitives A simple client-server interaction using acknowledged datagrams. 67 Chapter 1: Introduction 1.3 Network Software 1.3.5 The Relationship of Services to Protocols The relationship between a service and a protocol 68 Chapter 1: Introduction 1.3 Network Software 1.3.5 The Relationship of Services to Protocols A service defines what operations the layer is prepared to perform on behalf of its users, but it says nothing at all about how these operations are implemented. A protocol, in contrast, is a set of rules governing the format and meaning of the frames, packets, or messages that are exchanged by the peer entities within a layer. Entities use protocols in order to implement their service definitions. 69 Chapter 1: Introduction 1.4 Reference Models 1.4.1 The OSI Reference Model In the late 1970s, to promote the compatibility of network designs, the International Organization for Standardization (ISO) proposed an architecture model called the open systems interconnection references model (OSI model). services layer N PDUs (protocol data unit) layer N-1 layer N-1 layer N actual data flow on the lowest level 70 Chapter 1: Introduction 1.4 Reference Models 1.4.1 The OSI Reference Model What a mess! Much better! Note: May not be the most efficient! 71 Chapter 1: Introduction 1.4 Reference Models 1.4.1 The OSI Reference Model 72 Chapter 1: Introduction 1.4 Reference Models 1.4.1 The OSI Reference Model 7 application 6 presentation 5 session 4 3 transport 2 1 data link network physical network services (email, file transfer) formatting, encryption, and compression setup and management of end-to-end conversation end-to-end delivery of messages end-to-end transmission of packets transmission of packets on one given link transmission of bits 73 Chapter 1: Introduction 1.4 Reference Models 1.4.1 The OSI Reference Model 7 application 6 presentation 5 session 4 3 transport 2 data link 1 network physical Encapsulation H: header T: trail Each may be empty. data AH data PH AH data SH PH AH data TH SH PH AH data NH TH SH PH AH data DH NH TH SH PH AH data DT bit streams 74 Chapter 1: Introduction 1.4 Reference Models (Transmission Control Protocol/Internet Protocol 1.4.2 The TCP/IP Reference Model 75 Chapter 1: Introduction 1.4 Reference Models 1.4.2 The TCP/IP Reference Model The TCP/IP reference model with some protocols we will study 76 CHAPTER 1: INTRODUCTION Model used in this book 77 Chapter 1: Introduction 1.4 Reference Models A Comparison of the OSI and TCP/IP Reference Model The OSI reference model was devised before the (OSI) protocols were invented. •Not biased toward any one particular set of protocols •The designers did not have much experience with the subject and did mot have a good idea of which functionality to put in which layer 78 Chapter 1: Introduction 1.4 Reference Models A Comparison of the OSI and TCP/IP Reference Model With the TCP/IP, the protocols came first, and the model was really just a description of the existing protocols. The model did not fit any other protocol stacks. 7 layers versus 4 connection-oriented versus connectionless 79 Chapter 1: Introduction 1.4 Reference Models A Critique of the OSI Model and Protocols 1. Bad timing 2. Bad technology 3. Bad implementation 4. Bad politics 80 Chapter 1: Introduction 1.4 Reference Models A Critique of the OSI Model and Protocols Bad timing The apocalypse of the two elephants 81 Chapter 1: Introduction 1.4 Reference Models A Critique of the TCP/IP Reference Model 1. The model does not clearly distinguish the concepts of service, interface, and protocol. 2. The model is not general and is poorly suited to describing andother protocol stack. 3. The model does not distinguish (or even mention) the physical and data link layer. 4. Only TCP and IP are carefully thought out and implemented. Many other protocols are ad hoc. 82 CHAPTER 1: INTRODUCTION Example networks Internet ARPANET NSFNET Third-generation mobile phone networks Wireless LANs: 802.11 RFID and sensor networks 83 Chapter 1: Introduction 1.5 Example Networks 1.5.1 The Internet (a) Structure of the telephone system. (b) Baran’s proposed distributed switching system 84 Chapter 1: Introduction 1.5 Example Networks The ARPANET IMP: Interface Message Processor The original ARPANET design 85 Chapter 1: Introduction 1.5 Example Networks 1.5.1 The Internet Growth of the ARPANET (a) December 1969. (b) July 1970. (c) March 1971. (d) April 1972. (e) September 1972 86 Chapter 1: Introduction 1.5 Example Networks The NSFNET backbone in 1988 87 Chapter 1: Introduction 1.5 Example Networks Architecture of the Internet 88 Chapter 1: Introduction 1.5 Example Networks The Internet Society http://www.isoc.org A brief history of the Internet http://www.isoc.org/internet/history/brief.html Hobbes' Internet Timeline http://www.isoc.org/guest/zakon/Internet/History/HIT.html 89 Chapter 1: Introduction 1.5 Example Networks Ethernet Architecture of the original Ethernet 90 THIRD-GENERATION MOBILE PHONE NETWORKS (1) Cellular design of mobile phone networks Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education-Prentice Hall, 2011 91 THIRD-GENERATION MOBILE PHONE NETWORKS (2) Architecture of the UMTS 3G mobile phone network. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education-Prentice Hall, 2011 92 THIRD-GENERATION MOBILE PHONE NETWORKS (3) Mobile phone handover (a) before, (b) after. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education-Prentice Hall, 2011 93 Chapter 1: Introduction 1.5 Example Networks Wireless LANs: 802.11 (a) Wireless networking with a base station. (b) Ad hoc networking 94 CHAPTER 1: INTRODUCTION Signal Fading Multipath fading 95 Chapter 1: Introduction 1.5 Example Networks Wireless LANs The range of a single radio may not cover the entire system Hidden terminal problem 96 Chapter 1: Introduction 1.5 Example Networks Wireless LANs A multicell 802.11 network 97 RFID AND SENSOR NETWORKS (1) RFID used to network everyday objects. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education-Prentice Hall, 2011 98 RFID AND SENSOR NETWORKS (2) Multihop topology of a sensor network Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education-Prentice Hall, 2011 99 Chapter 1: Introduction 1.6 Network Standardization Benefits of standards De facto (from the fact) De jure (by law) standard 100 Chapter 1: Introduction 1.6 Network Standardization 1.6.1 Who’s Who in the Telecommunications World 101 Chapter 1: Introduction 1.6 Network Standardization 1.6.2 Who’s Who in the International Standards World 102 Chapter 1: Introduction 1.6 Network Standardization 1.6.2 Who’s Who in the International Standards World ITU • Main sectors • Radio communications • Telecommunications Standardization • Development • Classes of Members • National governments • Sector members • Associate members • Regulatory agencies 103 Chapter 1: Introduction 1.6 Network Standardization 1.6.2 Who’s Who in the International Standards World 104 Chapter 1: Introduction 1.6 Network Standardization 1.6.2 Who’s Who in the International Standards World The 802 working groups. The important ones are marked with *. The ones marked with are hibernating. The one marked with † gave up and disbanded itself. 105 Chapter 1: Introduction 1.6 Network Standardization 1.6.3 Who’s Who in the Internet Standards World 106 Chapter 1: Introduction 1.7 Metric Units The principal metric prefixes 107 Chapter 1: Introduction Exercises: 1. Compare the cost of Internet access at home between Taiwan and USA. Chapter Problems: 4, 8, 25, 35 108