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Introduction to Networking. Introduction Elements of a Network Architecture Layered Architecture Internetworks: The Internet Brief History of Networking Summary. 1. Introduction. What is a Computer Network?. a set of computers and/or switches connected by communication links

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Introduction to Networking


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    1. Introduction to Networking • Introduction • Elements of a Network Architecture • Layered Architecture • Internetworks: The Internet • Brief History of Networking • Summary 1

    2. Introduction What is a Computer Network? • a set of computers and/or switches connected by communication links • many ``topologies'' possible: • local area networks (LAN) versus wide-area networks (WAN)‏ • many different media: fiber optic, coaxial cable, twisted pair, radio, satellite For us:topology and mediaunimportant 2

    3. Introduction (continue)‏ a software/hardware infrastructure of Computer Network: • original justification: allows shared access to computing resources (e.g., computers, files, data)‏ • a mediumthrough which geographically dispersed users communicate (e.g., email, teleconferencing)‏ • a medium through which distributed services/applications are implemented • an electronic village • an information highway, national information infrastructure • cyberspace: "a consensual [environment] experienced daily by billions of operators, in every nation, ...." 3

    4. Introduction (continue)‏ Packet-Switching • data entering network divided into chunks called "packets'' • packets traversing network share network resources (e.g., link bandwidth, buffers) with other packets • on demand resource use: statistical resource sharing 4

    5. Introduction (continue)‏ Packet-Switching • resources demands may exceed resources available: • e.g., A and B packets arrive at R1, destined for C • resource contention:queuing (waiting), delay, loss 5

    6. Introduction (continue)‏ Circuit-Switched Network • all resources (e.g. communication links) needed by call dedicated to that call for duration • example: telephone network 6

    7. Introduction (continue)‏ Circuit-Switched Network • resource demands may exceed resources available • A and B want to call C • resource contention: blocking (busy signal)‏ • drawbacks: ?? • advantages: ?? 7

    8. Introduction (continue)‏ Resources Statical Sharing: advantages • save/make money! • example: 1 Mbit/sec link; each user requires 100 Kbits/sec when transmitting; each user has data to send only 10% of time. • circuit-switching: give each caller 100 Kbits/sec capacity. Can support 10 callers. • packet-switching: with 35 ongoing calls, probability that 10 or more callers simultaneously active is less than 0.0004! • can support many more callers, with small probability of` "contention.'' • if users are ``bursty'' (on/off), then packet-switching is advantageous (Baran, 1965)‏ 8

    9. Elements of a Network • communication links: • point-point (e.g., A-to-B)‏ • broadcast (e.g.,: Ethernet LAN)‏ • host: computer running applications which use network (e.g.: H1 • router: computer (often w/o applications-level programs) routing packets from input line to output line. (e.g., A->C)‏ • gateway: router directly connected to 2+ networks (e.g. A)‏ • network: set of node (hosts/routers/gateways) within single administrative domain • internet:collection of interconnected networks 9

    10. Elements of a Network Protocols • protocol: rules by which active network elements (applications, hosts, routers) communicate with each other • protocols define : • format/order of messages exchanged • actions taken on receipt of message • rules by which two or more people communicate to provide a service, or to get something done • protocols in every day life: 10

    11. Layered Architecture • complex system architecture simplified by layering. • layer N relies on services of layer N-1 to provide a service to layer N+1 • service from lower layer independent of how that service implemented • information/complexity hiding • layer N change doesn't affect other layers • interfaces define how services requested 11

    12. Layered Architecture (continue)‏ Layered Network Architecture • the network consists of geographically distributed hardware/software components • a distributedlayered view 12

    13. Layered Architecture (continue)‏ Layering and protocols • peer entities (e.g., processes) in layer N provide service by communicating (sending "packets") with each other, using communication service provided by layer N-1. • logical versus physical communication: 13

    14. Layered Architecture (continue)‏ The Internet and ISO/OSI reference model 14

    15. Layered Architecture (continue)‏ Layers of a protocol architecture • application layer • process-to-process communication • examples: WWW, email, teleconferencing, info. Retrieval • socket layer (Internet only)‏ • buffering and delivery of data at end systems • presentation layer (OSI only)‏ • conversion of data to a common format (e.g., little endian versus big-endian byte orders, integer and floating point numbers). • Internet stack: data conversion a user-level concern 15

    16. Layered Architecture (continue)‏ Layers of a protocol architecture (continue)‏ • session layer (OSI only)‏ • session set up (e.g., authentication), recovery from failure (broken session)‏ • a "thin" layer • transport layer • transport service: end-to-end delivery of data • may multiplex several streams from higher layers • sender/receiver speed matching • Internet: TCP and UDP 16

    17. Layered Architecture (continue)‏ Layers of a protocol architecture (continue)‏ • network layer • at end hosts: start packets on their way • at routers: control packet routing • bottleneck avoidance, congestion control • Internet: IP packets, BGP, RIP 17

    18. Layered Architecture (continue)‏ Layers of a protocol architecture (continue)‏ • data link layer • point-to-point error free communication over a single link • multiaccess LAN protocols • speed matching between sender/receiver • Ethernet, HDLC, PPP • physical layer: stuff of EE's • transmitting raw bits (0/1) over wire 18

    19. Internetworks: the Internet • an internet: interconnection of many networks • a network of networks • each network administered separately • the Internet: each network runs same software: the Internet protocols 19

    20. Internetwork: The Internet (continue)‏ Protocol Packets • packet: unit of data exchanged between protocol entities in a given layer • data at one layer encapsulated in packet at lower layer • “envelope within envelope” 20

    21. Internetwork: The Internet (continue)‏ Generic Issues in a Layer • error control: make “channel” more reliable • flow control: avoid flooding slower peer • fragmentation: dividing large data chunks into smaller pieces; reassembly • multiplexing: several higher level sessions share single lower level connection • connection setup: handshaking with peer • addressing/naming: locating, managing identifiers associated with entities 21

    22. Internetwork: The Internet (continue)‏ Generic Issues ina Layer (continue)‏ • layering has conceptual, structuring advantages but … • layer N may duplicate lower level functionality, e.g., error recovery hop-hop versus end-end • different layers may need same info (e.g., timestamp)‏ • layer N may need layer N-2 information (e.g., lower layer packet sizes)‏ 22

    23. Internetwork: The Internet (continue)‏ Comparing network, distributed systems and parallel processors Distributed system • application-level concerns and semantics: distributed file system, atomic remote actions • relies on network communication service to implement higher-level services Multiprocessors • processors connected by high-speed interconnect • “finer-grained” communication than network communication • link length limited to several meters • network/multiprocessor distinction can be blurred: network of workstations with high-speed interconnect 23

    24. A Brief History of Networking 1830: telegraph 1876:telephone (circuit-switching)‏ 1960’s: packet switching (Baran, Davies)‏ • Arpanet has 4 nodes 1970’s: • companies: DECnet, IBM SNA • Arpanet has 100 nodes 24

    25. A Brief History of Networking (continue)‏ 1980’s: • local area networks • late 80’s: 100 Mbps • proliferation of wide area networks: CSNET, MILNET, NSFNET, ARPANET • Internet passes 100,000 nodes in 1989 25

    26. A Brief History of Networking (continue)‏ 1990’s: • Arpanet, NSFnet retired: gov’t no longer provides backbone service • explosive growth: 10 million hosts in 1996 • 150Mbps, 660 Mbps • wireless networks • WWW drives Internet mania Current trends: • continued expansion • commercialization • security 26

    27. Summary • packet-switching versus circuit-switching • the pieces of a network architecture • layering 27

    28. Literature • Jim F. Kurose and Keith W. Ross. Computer Networks: A Top-Down Approach Featuring Internet. Adisson-Wesley, second edition, 2002. • Andrew S. Tannenbaum. Computer Networks. Prentice Hall PTR, fourth edition, 2003. 28

    29. Lectures Schedule • 2. Physical Layer • 3. Data Link Layer • 4. The Network Layer • 5. The Transport Layer • 6. Presentation Layer • 7. QoS Guarantees • 8. Multimedia Networking • 9. Integrated and Differentiated Services • 10. Network Security • 11. Network Management 29