Ch.1: Introduction Computer Networking Eliezer Dor (eliezer dor@ Teaching...

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Transcript of Ch.1: Introduction Computer Networking Eliezer Dor (eliezer dor@ Teaching...

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  • Ch.1: Introduction Computer Networking Eliezer Dor (eliezer dor@ Teaching Assistant: Allon Wagner 1
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  • Ch.1: Introduction Course Information Lectures: Thursday 5 8 Dach 005 Recitation: Tuesday 16 17, 17 18 Dan David 001 Web site: 1.Keshav : An Engineering Approach to Computer Networking 2.Tanenbaum : Computer Networks 3.Bertsekas and Gallager : Data Networks Kurose-Ross: A Top-down Approach to Computer Networking Main Book: 2/71 Additional Books:
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  • Ch.1: Introduction Practical Information Homework assignment: Mandatory Both theoretical and programming Grades: Final Exam: 60% theory exercises: 20% Programming exercises: 20% 3/71
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  • Ch.1: Introduction Chapter 1 4 Introduction
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  • Ch.1: Introduction Motivation 1 st stage society: Agriculture, handicraft 2 nd stage society: Industrial, labor intensive Today s society: automated industry with sophisticated logistics information intensive: business, knowledge, advertising, news, social interaction, recreation Future society is likely to be even more information-dominated 5/71
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  • Ch.1: Introduction The Purpose of the Network t serves network applications residing in hosts t applications at distinct hosts need to co-ordinate actions / co-operate t thus they need to communicate information to each other t network must deliver that information t to the right host t to the right application process / thread t network serves applications which serve users 6/71
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  • Ch.1: Introduction Information A representation of knowledge Examples: text, music, video, technical specifications software, instructions, reports, alarms Can be represented in two ways analog (pictures / ideograms) digital (bits) the Digital Revolution convert information as pictures to information as bits networks move around bits instead of pictures 7/71
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  • Ch.1: Introduction Challenges t make order in the jungle of applications t organize information into manageable units t keep track of info units sent/ moving/ received t take account of errors / misunderstandings etc. t move the bits through the network u find the destination host in the network jungle u using an efficient path u learn automatically the current network topology u make efficient use of link / router capacities u resolve competition for use of same resource u Cheaply, Securely, with Quality of Service, 8/71
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  • Ch.1: Introduction Internet Physical Infrastructure 9/71
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  • Ch.1: Introduction This course s Challenge To discuss this complexity in an organized way, so that we understand the issues / alternatives can follow/design/troubleshoot processes Need to divide the job into functional layers Understand the interrelation between them These problems are beyond a specific technology 10/71
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  • Ch.1: Introduction Early communications systems telegraph, telephone first used direct point to point links when number of users grew: introduced switching points/ configurable circuits each call had a dedicated circuit for its duration 11/71 Switched connection phone line trunk group
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  • Ch.1: Introduction Data Networks set of interconnected nodes exchanging information links are common usage switching node must: choose for each data unit a link bringing it closer to dest. schedule their transmission on the common usage links (resolve the competition for the usage of the link) 12/71
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  • Ch.1: Introduction Qwest backbone 13/71
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  • Ch.1: Introduction Networking Tasks phone net. soln Addressing - identify the end user phone number 1-201-222-2673 = country code + region code + exchange + number Routing Find route from source to destination. t determined from phone number by static routing tables Forwarding how information is moved t circuit switching::a fixed circuit along path to destination Information Units - How information is sent v oice samples; no addressing attached t samples sent continuously, 8000/sec t network must prepare source-dest. circuit in advance 14/71
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  • Ch.1: Introduction Networking Tasks Internet Solution Addressing - identify the end user IP addresses, = network number || host # Routing- How to get from source to destination routers learn automatically network topology build routing tables / updated frequently Forwarding how information is moved packet switching: move packets 1 by 1 through routers. Information Units - How information is sent. self-descriptive packet = data + header header contains destination address 15/71
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  • Ch.1: Introduction Telephone networks support a high end-to-end quality of service, but is expensive Internet supports no quality of service but is flexible and cheap Future networks will have to support a wide range of service qualities at a reasonable cost 16/71
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  • Ch.1: Introduction History 1961: Kleinrock shows effectiveness of packet-switching 1964: Baran - packet-switching concept in military networks 1967: ARPAnet by Advanced Research Projects Agency 1972: ARPAnet demonstrated publicly (15 nodes total) first transport. email, protocols 1970: ALOHAnet satellite network in Hawaii 1973: Metcalfe s PhD thesis proposes Ethernet 1974: Cerf and Kahn - architecture for internetworking late70 s: proprietary architectures: DECnet, SNA, XNA 1982-5: TCP/IP, SMTP mail, DNS, FTP 1988: TCP congestion control 1991: ARPAnet commercialized: NSFnet, Internet 1989-93: WWW, browser, http, html, URL 17/71 LAN idea
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  • Ch.1: Introduction Cerf and Kahn s internetworking principles: autonomy - no internal changes required to interconnect networks best effort service model stateless routers decentralized control Defines today s Internet architecture 18/71
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  • Ch.1: Introduction Why do we need Protocols Communication is between applications or other S/W entities Its objective: enable cooperation on a common task Need protocols to understand each other Semantics: what I report/ want of you to do Syntax/ format: how write/ read this info 19/71
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  • Ch.1: Introduction Open/ Proprietary Protocols Open protocol can be used by anyone it is published by a standards organization or a public consortium e.g. draft standard. standard Proprietary protocol is owned by a company may be used subject to companys agreement 20/71
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  • Ch.1: Introduction Why do we need Standards Communication happens between entities Hosts (personal computers, servers) Routers H/W entities produced by different vendors S/W applications/ OS entities also Need agreement to ensure correct, efficient and meaningful communication this is called Interworking 21/71
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  • Ch.1: Introduction Organizations that Issue Standards IETF (Internet Engineering Task Force) IEEE (Institute for Electrical and Electronic Engineers) ITU (International Telecommunications Union) ISO (International Organization for Standardization) W3C (World Wide Web Consortium) 22/71
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  • Ch.1: Introduction Why Layering Communication is a very complex task What we need is: communication btw applications at distant hosts What is reasonably feasible in one piece is: the ability to transfer a series of bits over a link We need to bridge between very sophisticated applications and very primitive physical layer What is needed is to divide the tasks functionality into well chosen parts each part should be reasonably easy to do they should work well together 23/71
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  • Ch.1: Introduction How to do Layering Define a conceptual Layering Model means: what is the function of each layer how they cooperate / use each others services Set principles for proper usage of the model Build protocols for each layer protocol is between same layer entities @ distinct nodes there may be several protocols in each layer providing different type service for the layers function Define interfaces between layers interface (here) is between distinct layer entities at same node (computing device) 24/71
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  • Ch.1: Introduction Layering Principles Modularity each layer works independently of the others information exchange only according to Interfaces defined in the Model analogous to the Object Oriented principle in S/W eng. this means: dont change/peek into internal variables of other layers modularity is bypassed very seldom only when there is no other solution to a problem Transparency layering should be invisible to user 25/71
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  • Ch.1: Introduction Layering Benefits Layering enables: discussion/understanding of the issues enables clear visualizing of relationships btw. functions its impossible to think about all layers @ once efficient development of protocols each layer has a different functional focus no need to think other layers when designing it easy replacement/maintenance of protocols as long as modularity & interfaces are adhered to Layering is a good reference model for discussion 26/71
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  • Ch.1: Introduction A mail system layering model 27/71
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