access to computers and the internet has become a basic need for education in our society. kent...
TRANSCRIPT
CHAPTER 1 INTRODUCTION
Access to computers and the Internet has become a basic need for education in our society. Kent Conrad (US Senator)
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CHAPTER 1: INTRODUCTION
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Chapter 1: Introduction
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CHAPTER 1: INTRODUCTION
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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。
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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。
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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。
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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。
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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。
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CHAPTER 1: INTRODUCTION
Why is all this happening? Because of the Internet!
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Chapter 1: Introduction
Computer Networks vs. Distributed Systems
Users make the decision. O.S. makes the decision.
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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.
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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.
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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)
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Chapter 1: Introduction
1.1 Uses of Computer Networks
Client-server model
1.1.1 Business Applications
A network with two clients and one server.
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Chapter 1: Introduction
1.1 Uses of Computer Networks
1.1.1 Business Applications
The client-server model involves requests and replies.
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Chapter 1: Introduction
1.1 Uses of Computer Networks
Client-server model server type
Concurrent server vs. Iterative server
Stateful server vs. Stateless server
1.1.1 Business Applications
Examples:
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Chapter 1: Introduction
1.1 Uses of Computer Networks
1.1.2 Home Applications
• Access to remote informationWorld Wide Web• Person-to-person communicationElectronic mail, IM, Videoconference• Interactive entertainmentVideo-on-Demand, Games• Electronic commerce• Social networks
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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.
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CHAPTER 1: INTRODUCTION
BitTorrent Instant Messaging Twitter Facebook, Google+ Wikipedia
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Chapter 1: Introduction
1.1 Uses of Computer Networks
1.1.2 Home Applications
Some forms of e-commerce.
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CHAPTER 1: INTRODUCTION
IPTV Ubiquitous Computing Sensor networks Power-line networks RFID (Radio Frequency Identification)
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Chapter 1: Introduction
1.1 Uses of Computer Networks
1.1.3 Mobile Users
Combinations of wireless networks and mobile computing.
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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
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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
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CHAPTER 1: INTRODUCTION
Social Issues Network Neutrality DMCA (Digital Millennium Copyright Act),
DRM (Digital Rights Management) Profiling and cookies Botnet (DDoS) Phishing CAPTCHA
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Chapter 1: Introduction
1.1 Uses of Computer Networks
1.1.4 Social Issues
PrivacyCopyrightPornographyAnonymitySecurityWorms and Virusfreedom of speech vs. censorshipresponsibility of the service providers…
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Chapter 1: Introduction
1.2 Network Hardware
Broadcast Networks
shared link (may be wireless)
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Chapter 1: Introduction
1.2 Network Hardware
Point-to-point Networks
point to point link
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CHAPTER 1: INTRODUCTION
Packet Unicast, Multicast, Broadcast PAN, LAN, MAN, WAN Interplanetary Internet
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Chapter 1: Introduction1.2 Network Hardware
Classifying by scales
Classification of interconnected processors by scale.
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CHAPTER 1: INTRODUCTION
Personal Area Networks Bluetooth RFID
Bluetooth PAN configuration
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Chapter 1: Introduction
1.2 Network Hardware
Local Area Networks
IEEE 的定義：A LAN (Local Area Network) is a data communication systemallowing a number of independent devices to communicate directly with each other, within a moderately sized geographicarea over a physical communication channel of moderate datarates.
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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...)
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Chapter 1: Introduction
1.2 Network Hardware
Local Area Networks
Ethernet
Token Ring
Two broadcast networks(a) Bus(b) RingWireless and wired LANs. (a)
802.11. (b) Switched Ethernet
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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)
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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
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CHAPTER 1: INTRODUCTION
Virtual LAN
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Chapter 1: Introduction
1.2 Network Hardware
Metropolitan Area Networks
A metropolitan area network based on cable TV.
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CHAPTER 1: INTRODUCTION
Wireless MAN 3G->4G WiMax (Worldwide Interoperability for
Microwave Access) LTE (Long Term Evolution)
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CHAPTER 1: INTRODUCTION
WAN
WAN that connects three branch offices in Australia
WAN using a virtual private network
WAN using an ISP network
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Chapter 1: Introduction
1.2 Network Hardware
Wide Area Networks
Relation between hosts on LANs and the subnet.
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Chapter 1: Introduction
1.2 Network Hardware
Wide Area Networks
A stream of packets from sender to receiver.
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Chapter 1: Introduction
store-and-forward network
A
B
CA sends a message to C through B.
B must store this message until B is sure that C has received it.
Store first, then forward. But when to start forwarding?
1.2 Network Hardware
Wide Area Networks
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Chapter 1: Introduction
A
B
CA sends a message to C through B.
When to starting forwarding?
1. After the message is completely received2. Start forwarding after a fixed amount of information(bits) received3. Start forwarding immediately after receiving data (cut-through)
store-and-forward network
1.2 Network Hardware
Wide Area Networks
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Chapter 1: Introduction
A
B
CA sends a message to C through B.
If a message takes 1 minute to travel a link:
(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)
0 m10.25 m2 m10.5 m3 m2 m10.75 m4 m3 m21.0 m4 m31.25 m4
A B Cstore-and-forward network
1.2 Network Hardware
Wide Area Networks
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Chapter 1: Introduction
The concept of pipeliningIf the message is decomposed into N packets, each packet takes1/N minutes to travel a link. It takes 2 1
N
N
N
minutes.
但分的愈細愈好嗎 ?
bits
header user information trailer
h t
overhead for N packets=N(h+t)overhead for 1 message=h+t
1.2 Network Hardware
Wide Area Networks
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Chapter 1: Introduction
SwitchingA
B
C
D
E
F
G
H
(1) circuit switching (in telephone)(2) packet switching(3) message switching
Current Internet practice: store-and-forward packet switching
Wide Area Networks:Dod: ARPANET in 1960s (become Internet)IBM: SNA in 1974DEC: DECNET in 1975CCITT X.25 in 1970s
1.2 Network Hardware
Wide Area Networks
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Switching
Chapter 1: Introduction
Bottleneck in current store-and-forward packet switching network:ROUTING
router
packets delayed (or even discarded) in routers
1.2 Network Hardware
Wide Area Networks
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1.2 Network Hardware
Wireless Networks
Chapter 1: Introduction
The fast-growing segment of the industry:• notebook computers• personal digital assistants• cellular phones
Before long, we would have:• palmtop computers• wristwatch computers• …
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1.2 Network Hardware
Wireless Networks
Chapter 1: Introduction
Categories of wireless networks:1. (used for) System interconnection2. Wireless LANs3. Wireless WANs
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1.2 Network Hardware
Wireless Networks
Chapter 1: Introduction
(a) Bluetooth configuration(b) Wireless LAN
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1.2 Network Hardware
Wireless Networks
Chapter 1: Introduction
(b) is more efficient and economical.
NEMO: NEtwork MObility
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1.2 Network Hardware
Home Networks
Chapter 1: Introduction
1. Computers (desktop PC, PDA, shared peripherals2. Entertainment (TV, DVD, VCR, camera, stereo, MP3)3. Telecomm (telephone, cell phone, intercom, fax)4. Appliances (microwave, fridge, clock, furnace, airco, lights)5. Telemetry (utility meter, smoke/burglar alarm, thermostat, babycam).
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1.2 Network Hardware
Internetworks
Chapter 1: Introduction
NII: National Information Infrastructure -> GII (Global II)
Information Superhighway
Networking is a world wide phenomenon.
Internet
Next Generation Internet
Internet II
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Internet Usage
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Chapter 1: Introduction1.3 Network Software
1. Protocol Hierarchies2. Design Issues for the Layers3. Connection-Oriented and Connectionless Services4. Service Primitives5. The Relationship of Services to Protocols
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Chapter 1: Introduction1.3 Network Software
1.3.1 ProtocolHierarchies
peers
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Chapter 1: Introduction1.3 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.
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French
The common Dutchcan be replaced with another.
Email can be usedinstead of fax.
An analogy
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Chapter 1: Introduction1.3 Network Software
Example information flow supporting virtual communication in layer 5
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Chapter 1: Introduction1.3 Network Software
Relations between layers at an interface
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Chapter 1: Introduction1.3 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)
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Chapter 1: Introduction1.3 Network Software
1.3.3 Connection-Oriented and Connectionless Services
Six different types of service
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Chapter 1: Introduction1.3 Network Software
1.3.3 Connection-Oriented and Connectionless Services
Initial Destination Packet Error Flow Optionsetup address sequence control control negotiationIssue
Connection Oriented
Connection-less
required
notpossible
only neededduring setup
needed forevery packet
guaranteed
notguaranteed
by networklayer
by transportlayer
by transportlayer
by networklayer
Yes
No
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Chapter 1: Introduction1.3 Network Software
1.3.4 Service Primitives
Five service primitives for implementing a simple connection-oriented service
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Chapter 1: Introduction1.3 Network Software
1.3.4 Service Primitives
A simple client-server interaction using acknowledged datagrams.
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Chapter 1: Introduction1.3 Network Software
1.3.5 The Relationship of Services to Protocols
The relationship between a service and a protocol
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Chapter 1: Introduction1.3 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.
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Chapter 1: Introduction1.4 Reference Models
1.4.1 The OSI Reference Model
In the late 1970s, to promote the compatibility of networkdesigns, the International Organization for Standardization(ISO) proposed an architecture model called the opensystems interconnection references model (OSI model).
layer N
layer N-1
layer N
layer N-1PDUs (protocol data unit)
actual data flow on the lowest level
services
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Chapter 1: Introduction1.4 Reference Models
1.4.1 The OSI Reference Model
What a mess! Much better!
Note: May not be themost efficient!
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Chapter 1: Introduction1.4 Reference Models
1.4.1 The OSI Reference Model
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Chapter 1: Introduction1.4 Reference Models
1.4.1 The OSI Reference Model
applicationapplication
presentation
session
transport
network
data link
physical
7
6
5
4
3
2
1 transmission of bits
transmission of packets on one given link
end-to-end transmission of packets
end-to-end delivery of messages
setup and management of end-to-end conversation
formatting, encryption, and compression
network services (email, file transfer)
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Chapter 1: Introduction1.4 Reference Models
1.4.1 The OSI Reference Model
applicationapplication
presentation
session
transport
network
data link
physical
7
6
5
4
3
2
1
Encapsulation data
dataAH
dataAHPH
dataAHPHSH
dataAHPHSHTH
dataAHPHSHTHNH
dataAHPHSHTHNH
bit streams
DT
H: headerT: trailEach may be empty.
DH
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Chapter 1: Introduction1.4 Reference Models
1.4.2 The TCP/IP Reference Model
(Transmission Control Protocol/Internet Protocol
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Chapter 1: Introduction1.4 Reference Models
1.4.2 The TCP/IP Reference Model
The TCP/IP reference model with some protocols we will study
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CHAPTER 1: INTRODUCTION
Model used in this book
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Chapter 1: Introduction1.4 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
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Chapter 1: Introduction1.4 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 4connection-oriented versus connectionless
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Chapter 1: Introduction1.4 Reference Models
A Critique of the OSI Model and Protocols
1. Bad timing2. Bad technology3. Bad implementation4. Bad politics
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Chapter 1: Introduction1.4 Reference Models
A Critique of the OSI Model and Protocols
Bad timing
The apocalypse of the two elephants
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Chapter 1: Introduction1.4 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.
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CHAPTER 1: INTRODUCTION
Example networks Internet ARPANET NSFNET Third-generation mobile phone networks Wireless LANs: 802.11 RFID and sensor networks
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Chapter 1: Introduction1.5 Example Networks
1.5.1 The Internet
(a) Structure of the telephone system.(b) Baran’s proposed distributed switching system
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Chapter 1: Introduction1.5 Example Networks
The ARPANET
The original ARPANET design
IMP: Interface Message Processor
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Chapter 1: Introduction1.5 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
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Chapter 1: Introduction1.5 Example Networks
The NSFNET backbone in 1988
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Chapter 1: Introduction1.5 Example Networks
Architecture of the Internet
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Chapter 1: Introduction1.5 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
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Chapter 1: Introduction1.5 Example Networks
Ethernet
Architecture of the original Ethernet
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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
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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
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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
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Chapter 1: Introduction1.5 Example Networks
Wireless LANs: 802.11
(a) Wireless networking with a base station.(b) Ad hoc networking
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CHAPTER 1: INTRODUCTION
Signal Fading
Multipath fading
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Chapter 1: Introduction1.5 Example Networks
Wireless LANs
The range of a single radio may not cover the entire system
Hidden terminal problem
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Chapter 1: Introduction1.5 Example Networks
Wireless LANs
A multicell 802.11 network
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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
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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
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Chapter 1: Introduction1.6 Network Standardization
De facto (from the fact)De jure (by law)
Benefits of standards
standard
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Chapter 1: Introduction1.6 Network Standardization
1.6.1 Who’s Who in the Telecommunications World
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Chapter 1: Introduction1.6 Network Standardization
1.6.2 Who’s Who in the International Standards World
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ITU• Main sectors
• Radio communications• Telecommunications Standardization• Development
• Classes of Members• National governments• Sector members• Associate members• Regulatory agencies
Chapter 1: Introduction1.6 Network Standardization
1.6.2 Who’s Who in the International Standards World
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Chapter 1: Introduction1.6 Network Standardization
1.6.2 Who’s Who in the International Standards World
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Chapter 1: Introduction1.6 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.
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Chapter 1: Introduction1.6 Network Standardization
1.6.3 Who’s Who in the Internet Standards World
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Chapter 1: Introduction1.7 Metric Units
The principal metric prefixes
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Chapter 1: Introduction
Exercises:
1. Compare the cost of Internet access at home between Taiwan and USA.
Chapter Problems:4, 8, 25, 35