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Computer Networks

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  1. Computer Networks Introduction Introduction -- February 2006

  2. User view Network hardware Network architecture Reference models Connections? Sliding window protocols Local area networks Routing Internet Security Performance Overview Introduction -- February 2006

  3. Models for computer usage 1960 ... 1970 ... Old, obsolete model mainframe Non graphical terminals Introduction -- February 2006

  4. server PC or workstation Models for computer usage 1980 ... Introduction -- February 2006

  5. Why Networks? • Business Applications • Home Applications • Mobile users • Resource sharing • Data • Equipment • programs • Communication medium • E-mail • Tools for cooperation • Videoconferencing • E-commerce Introduction -- February 2006

  6. Why Networks? • Business Applications • Home Applications • Mobile users • Access to remote information • WWW: newspapers, digital library • Person-to-person communication • E-mail • Instant messaging • Peer-to-peer communication • Interactive entertainment • E-commerce Introduction -- February 2006

  7. Why Networks? • Business Applications • Home Applications • Mobile users • Mobile <> wireless • Current usage: • portable office • computer conferences • wireless campus network • New: • wireless parking meters • vending machines • utily meter reading • merger of PDAs and cell phones • wearable computers Introduction -- February 2006

  8. User view • Communication subnet = communication infrastructure • Computer network = communication infrastructure+interconnected computers • Distributed system= computer network + transparency Introduction -- February 2006

  9. User view Network hardware Network architecture Reference models Connections? Sliding window protocols Local area networks Routing Internet Security Performance Overview Introduction -- February 2006

  10. Network hardware • Taxonomy: 2 dimensions • Technology: • broadcast, • point-to-point • Scale … Introduction -- February 2006

  11. Network hardware • Broadcast networks • Single shared channel • Address field to indicate destination • Easy broadcast to all destinations • Point-to-point networks • Routers, switches • Point-to-point lines • Routing Store and forward Introduction -- February 2006

  12. Network hardware • Scale: • local area networks • metropolitan area networks • wide area networks • wireless networks • home networks Introduction -- February 2006

  13. Network hardware • Within one building • No routers • Interface board in PC • Bus- of ring network • Shared medium Local area networks Introduction -- February 2006

  14. Network hardware • Covers a city • Cable TV + … • Shared medium Metropolitan area networks Introduction -- February 2006

  15. S1 S2 S3 S4 A B Network hardware Wide area networks • Routers, switches • Communication lines Routing A  B S1  S3 S1  S4  S3 S1  S2  S4  S3 Introduction -- February 2006

  16. Network hardware Wireless networks • System interconnection • Wireless LANs • Wireless WANs • System interconnection: • components of a computer • short-range radio • Bluetooth • configuration? NO Introduction -- February 2006

  17. Network hardware Wireless networks • System interconnection • Wireless LANs • Wireless WANs • Wireless LANs: • no cabling • base station or peer-to-peer • IEEE 802.11a: - 11Mbps • IEEE 802.11g: - 54 Mbps Introduction -- February 2006

  18. Opportunities: Computers: PC, notebook, PDA,… Entertainment: TV, DVD, VCR, camcorder, mp3 Telecommunications: Telephone, mobile, fax Appliances: Microwave, clock,… Telemetry: Smoke alarm, thermostat Challenges: Easy to install Foolproof in operation Low price Sufficient capacity Scalable , stable interfaces Secure en reliable Network hardware Home Networks Introduction -- February 2006

  19. User view Network hardware Network architecture Reference models Connections? Sliding window protocols Local area networks Routing Internet Security Performance Overview Introduction -- February 2006

  20. Network architecture • Communication rather complex • Reliable bit transport • Finding appropriate route • Fragmentation of packets • … • Systematic approach • Protocol + layered architecture Introduction -- February 2006

  21. Network architecture • Protocol • “rules” • kind of messages, composition of a message • Permitted responses to a message (= another message!) • Service • For the users of an “entity” • ex. reliable transport of a packet entity entity Introduction -- February 2006

  22. Network architecture • Layered architecture Logical comm. protocol 2 entity entity layer 2 service service protocol 1 entity entity layer 1 Introduction -- February 2006

  23. Network architecture • Layered architecture protocol 2 entity entity Layer 2 service service protocol 1 entity entity Layer 1 Introduction -- February 2006

  24. Ik vind dat menmensen niet magklonen. Filosoof (Tokio) taal Tolk • telefoon • fax • (brief) comm. kanaal telefoonnetwerk Secretaresse Network architecture • Ex1.: Communication between people Filosoof (Gent) Tolk Secretaris Introduction -- February 2006

  25. Ik vind dat menmensen niet magklonen. Filosoof (Tokio) taal Tolk • telefoon • fax • (brief) comm. kanaal telefoonnetwerk Secretaris Network architecture • Ex1.: Communication between people Introduction -- February 2006

  26. Network architecture • Ex2.: Communication between 2 Processes • Process A on computer x requests process B on computer y to send “letter.doc” Process A Process B letter.doc x y Introduction -- February 2006

  27. Network architecture Example • Protocol Send “letter.doc” B A 1200 bytes OK Dear rector, ... OK x y Introduction -- February 2006

  28. Network architecture Example • Protocol: “dialogue” • How messages are transmitted important • Transport layer: comm. between. processesidentification: (system name, process name) • Network layer: transport through networkidentification: system name Introduction -- February 2006

  29. Processes A B Processes B C D Processen B D Transport Transport Transport Network Network Network Network architecture Example x y Communicatie-netwerk z Introduction -- February 2006

  30. send “letter.doc” x, A y, B send “letter.doc” send “letter.doc” send “letter.doc” B, A Network architecture Example Process A Process B Transport layer on x Transport layer on y Introduction -- February 2006

  31. y x B, A y, x Y, X B, A B, A B, A Network architecture Example Transport layer on x Transport layer on y Network layer on x Network layer on y Introduction -- February 2006

  32. B, A B, A send “letter.doc” Network architecture Example send “letter.doc” Represent by : Introduction -- February 2006

  33. B, A send “letter.doc” B, A B, A send “letter.doc” send ... y, x B, A send “letter.doc” Network architecture Example Process A send “letter.doc” Process B y, B send “letter.doc” send “letter.doc” x, A Transport-layer on x Transport-layer on y y x Network-layer on x Network-layer op y Introduction -- February 2006

  34. process data transportheader process data networkheader transportheader process data Network architecture Example Introduction -- February 2006

  35. User view Network hardware Network architecture Reference models OSI Internet Connections? Sliding window protocols Local area networks Routing Internet Security Performance Overview Introduction -- February 2006

  36. OSI Reference model • Network design = complex • Decomposition:  ways • OSI: Open System Interconnection • open: comm. between different systems • reference: framework for new protocols • functionality of each layer defined • various protocols can realise the functionality of a layer Introduction -- February 2006

  37. S1 S2 S3 S4 y OSI Reference model • 7 layers: • Top 4 : between interconnected end systems • Lower 3: between end system and network x Introduction -- February 2006

  38. protocol application layer application application protocol presentation layer presentation presentation protocol session layer protocol transport layer session session transport transport protocol netw. layer protocol data link network network N N protocol phys. layer data link Data link D D system x S1 S4 system y physical physical F F OSI Reference model Introduction -- February 2006

  39. OSI Reference model • Physical layer transport of bits over physical cable • kind of cable • characteristics of connectors • presentation of bits on cable • data rate Introduction -- February 2006

  40. From data link layer To data link layer L2 data L2 data Physical layer Physical layer 101010000010111 101010000010111 OSI - Physical layer Introduction -- February 2006

  41. OSI Reference model • Data link layer creation of an error free comm. channel • framing • detection of errors • flow control • Access control Introduction -- February 2006

  42. H2 H2 T2 T2 OSI – Data link layer From network layer To network layer L3 data L3 data Data link layer Data link layer L2 data L2 data To physical layer From physical layer Introduction -- February 2006

  43. End system End system End system Intermediate system Intermediate system Intermediate system C B E D F A B OSI – Data link layer A E F Data link layer Physical layer Hop-to-hop delivery Hop-to-hop delivery Hop-to-hop delivery Introduction -- February 2006

  44. OSI Reference model • Network layer traffic of packets through 1/# networks • 2 kinds of service: • virtual connections • datagram service • Routing • Accounting • Interconnection of networks+ routing through these networks Introduction -- February 2006

  45. OSI – Network layer From transport layer To transport layer L4 data L4 data Network layer Network layer H3 H3 L3 data L3 data To data link layer From data link layer Introduction -- February 2006

  46. End system End system End system Intermediate system Intermediate system Intermediate system E C B F A D A B E F Data link layer Physical layer End-to-end delivery OSI – Network layer Network layer Introduction -- February 2006

  47. OSI Reference model • Transport layer communication channel between processes • Services – service-point addressing • Reliable transport • Datagram service • Broadcast/multicast • Make efficient use of networks • Multiplexing: multiple transport connections on a single network connection • Multiple connections between end systems • Segmentation + reassembly • Flow control Introduction -- February 2006

  48. OSI Reference model • Session layer Support the cooperation between processes using a reliable communication channel • Dialogue control: • ex. one sender at a time • Synchronisation (to restart dialogue after errors) Introduction -- February 2006

  49. OSI Reference model • Presentation layer preserve semantics of information • Choice of representation of data “on the wire” • ASCII or EBCDIC • 16-bit, 32-bit, … integers with 2-complement representation • ... • Encryption of data • Compression of data Introduction -- February 2006

  50. OSI Reference model • Application layer highest layer • applications, written by users • driving of a robot, electronic money transfer, … • standard applications • Electronic mail (X400) • Transfer of files (FTAM) • Subproblems: RPC (remote procedure call) Introduction -- February 2006