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Petros KAVASSALIS

Computer Networks and Communications [Δίκτυα Υπολογιστών και Επικοινωνίες] Lectures 2&3: What is the Internet? Univ. of the Aegean Financial and Management Engineering Dpt. Petros KAVASSALIS. What you will learn in this course.

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Petros KAVASSALIS

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  1. Computer Networks and Communications[Δίκτυα Υπολογιστών και Επικοινωνίες]Lectures 2&3: What is the Internet?Univ. of the Aegean Financial and Management Engineering Dpt Petros KAVASSALIS

  2. What you will learn in this course • A set of fundamental concepts for understanding Data Networks and the Internet • What is the Internet? • Internet architecture and layers • Internet applications and services • New concepts in the evolution of the Internet • The Internet goes Wireless… • Familiarization with the structure and organization of Digital Networks • Business and Social Networks • Electronic Markets and Online Feedback Mechanisms

  3. Who am I? • PhDinEconomicsandManagement (Univ. ParisDauphine & Ecolepolytechnique) • Research experience • Ecolepolytechnique, Paris • MIT CenterofTechnologyPolicyandIndustrialDevelopment, MIT CTPID (MIT Internet TelecommunicationsConvergenceConsortium) • Current positions • Univ. of the Aegean (FME): Assoc. Professor • RACTI: Director of ATLANTIS Group

  4. Communication tools • e-mail: pkavassalis [at] atlantis-group.gr • Course web site: see fme website

  5. Course Textbook[http://books.google.gr/books?id=Pd-z64SJRBAC&dq=tanenbaum+networks&printsec=frontcover&source=bn&hl=el&ei=ml-dSfH9L4S2jAeJ5L3ZBQ&sa=X&oi=book_result&resnum=4&ct=result]

  6. Supplementary Texts & References William Stallings, Computer Networking with Internet Protocols, Prentice Hall, 2004 James F. Kurose and Keith W. Ross, Computer Networking: A Top-Down Approach, Addison-Wesley, 2008

  7. Students evaluation • Class Participation (20%) + • Assignments (20%) + • Final Exam (60%)

  8. What is a network? • A hardware and software communications system formed by the interconnection of three or more devices • Devices may include: • Telephones • PCs • Routers • Other communications devices (please give examples)

  9. The geography of the Internet

  10. Mobile network Global ISP Home network Regional ISP Institutional network Internet in a nutshell • Protocols control sending, receiving of msgs • e.g., TCP, IP, HTTP, IM, Ethernet • Composition: “network of networks” • loosely hierarchical • public Internet versus private intranet • Standards • RFC: Request for comments • IETF: Internet Engineering Task Force

  11. Overview of the Internet The structure of the Internet is roughly hierarchical

  12. Tier-1 providers interconnect (peer) privately A multilevel structure: Tier 1 Tier 1 ISP Tier 1 ISP Tier 1 ISP • At center: “Tier-1” ISPs (e.g., Verizon, France Telecom, Deutche Telecom etc.), national/international coverage • Treat each other as equals / interconnect privately

  13. A multilevel structure: Tier 2 • Tier-2” ISPs: smaller (regional) ISPs (OTEnet, Forthnet) • Connect to one or more tier-1 ISPs, possibly other Tier 2 ISPs

  14. Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP A multilevel structure: Tier 3 Tier 1 ISP Tier 1 ISP Tier 1 ISP • “Tier-3” ISPs and local ISPs • Last hop (“access”) network (closest to end systems)

  15. Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP As a result, packet passes through many network infrastructures local ISP local ISP Tier 1 ISP Tier 3 ISP local ISP local ISP Tier 1 ISP Tier 1 ISP local ISP local ISP local ISP local ISP Which networks? Let’s discover the Internet…

  16. Mobile network Global ISP Home network Regional ISP Institutional network The essential of Internet: infrastructures but also applications… • Communication infrastructure enables various distributed applications • E-mail, Web browsing, Skypying, file sharing, online games • Communication applications are supported by • reliable data delivery from source to destination • “best effort” (unreliable) data delivery

  17. … “separated” in two blocks • IP (spanning-layer) separates information bitways from applications • Applications may work over multiple substrates (network techs) and these substrates do not pre-specify the development of new applications • [I will come back!]

  18. What is a protocol? • Human protocols • “what’s the time?” • “I have a question” • Introductions (“this is…”) • Specific msgs sent • Specific actions taken when msgs received, or other events • Machine protocols • Machines “talk each other” (rather than humans) • All communication activity in Internet governed by protocols • Protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

  19. Human and Computer protocols http:www.atlantis-group.gr Make possible a series of interactions

  20. The Internet path of a communication (defined with the use of a protocol): end-core-end • Internet end and core • mesh of interconnected routers • how is data transferred through net? • circuit switching: dedicated circuit per call: telephone net • packet-switching: data sent thru net in discrete “chunks

  21. Transmission speed • Measured in bits per second (bps) • Increasing factors of 1,000 … • Not factors of 1,024 • Kilobits per second (kbps) - note the lowercase k • Megabits per second (Mbps) • Gigabits per second (Gbps) • Terabits per second (Tbps) • The rule for writing speeds (and metric numbers in general) in proper form is that there should be 1 to 3 places before the decimal point • 23.72 Mbps is correct (2 places before the decimal point).\ • 2,300 Mbps has four places before the decimal point, so it should be rewritten as 2.3 Gbps (1 place)

  22. Circuit-switching (1) • End-end resources reserved for “call” • Link bandwidth, switch capacity • Dedicated resources: no sharing • Circuit-like (guaranteed) performance • Call setup required

  23. Example: 4 users FDM frequency time TDM frequency time Circuit-switching (2) • Network resources (e.g., bandwidth) divided into “pieces” • Pieces allocated to calls • Resource piece idle if not used by owning call (no sharing) • Dividing link bandwidth into “service lines” • Frequency division (FDM) • Time division (TDM)

  24. Packet-switching (1) • Each end-end data stream divided into packets • User A, B packets share network resources • Each packet uses full link bandwidth • Resources used as needed • Resource contention: • Aggregate resource demand can exceed amount available • Congestion: packets queue, wait for link use • Mechanism: store and forward: packets move one hop at a time • Node receives complete packet before forwarding

  25. D E Packet-switching (2): statistical sharing 100 Mb/s Ethernet C A statistical multiplexing 1.5 Mb/s B queue of packets waiting for output link Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand

  26. Packet-switching (3): store-and-forward L R R R • Takes L/R seconds to transmit (push out) packet of L bits on to link at R bps • Store and forward: entire packet must arrive at router before it can be transmitted on next link • Delay = 3L/R (assuming zero propagation delay) • Example: • L = 7.5 Mbits, R = 1.5 Mbps • Transmission delay = 15 sec

  27. Packet-switching v. Circuit-switching N users 1 Mbps link • 1 Mb/s link • Each user: • 100 kb/s when “active” • active 10% of time • Circuit-switching: 10 users • Packet switching: more users can share the network

  28. Packet-switching: pros and cons • Great for bursty data • Resource sharing • Simpler, no call setup • Excessive congestion: packet delay and loss • Protocols needed for reliable data transfer, congestion control • How to provide circuit-like behavior? • Bandwidth guarantees needed for audio/video apps • (Still) a not fully unsolved problem

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