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Introduction to computer networking

Introduction to computer networking. Internet: the global communications network. Internet. Text, audio, image and video: multimedia communications in the Internet.

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Introduction to computer networking

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  1. Introduction to computer networking

  2. Internet: the global communications network Internet

  3. Text, audio, image and video: multimedia communications in the Internet bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits and more bits… Browser “www.youtube.com” server

  4. Coding black and white images pixel grey level = luminance

  5. Coding black and white images 1 bit/pixel 21levels 2 bits/pixel 22levels

  6. Coding black and white images 3 bits/pixel 23levels 4 bits/pixel 24levels

  7. Coding black and white images pixel luminance (8 bits/pixel = 256 grey levels) 576 lines X 720 columns = 414720 pixels 414720 pixels X 8 bits/pixel = 3.318 Megabits

  8. Colour and motion – video coding Luminance + (two) Chrominances = 576 X 720 + 2 X 576 X 360 = 829440 pixels 829440 pixels X 8 bits/pixel X 25 images/s = 166 Mbits/s

  9. Compression is needed… and possible! Video at 166 Mbit/s Music at 1.4 Mbit/s Voice at 64 Kbits/s Compression explores redundancy and irrelevancein multimedia information

  10. Compression is needed … and possible

  11. Compression systems

  12. Internet: a packet switching network 0 1 1 0 0 1 0 1 packet 1 0 1 0 Internet 0 1 1 0

  13. “Surfing the net” Internet Packet 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110

  14. Routing packets link router 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110

  15. Routing packets link router 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110 00001010100100101101101001101110

  16. Internet structure: network of networks Internet Mobile network ISP Router ISP Domestic network Organizational network

  17. roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage treat each other as equals Tier-1 providers interconnect (peer) privately Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

  18. POP: point-of-presence to/from backbone peering … …. … … … to/from customers Tier-1 ISP: e.g., Sprint

  19. “Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier-2 ISPs also peer privately with each other. • Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet • tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

  20. “Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems) 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 Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

  21. a packet passes through many networks! Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

  22. Internet addressing Internet 153.3.2.1 153.4.2.1 11.15.2.33 153.3.2.2 11.23.35.2 20.18.3.2 153.4.2.2 128.45.138.1 15.53.19.21 15.54.18.20 20.18.3.1 192.26.12.1 192.26.1.1 128.45.233.8 192.26.5.1 192.26.1.29 Matilde 128.45.233.7 192.26.12.1 192.26.1.30 128.45.233.6 192.26.5.84 192.26.5.83 Run ipconfig IP address Pedro Rui João Teresa Rosário 232 = 4.294.967.296 addresses!

  23. Internet names - DNS hawai.com 153.3.2.1 153.4.2.1 www.ist.utl.pt 11.15.2.33 153.3.2.2 praia.edu 11.23.35.2 20.18.3.2 153.4.2.2 128.45.138.1 alameda.ist.utl.pt 15.53.19.21 taguspark.ist.utl.pt 15.54.18.20 20.18.3.1 192.26.12.1 192.26.1.1 128.45.233.8 192.26.5.1 bronze.praia.pt 192.26.1.29 beethoven.ist.utl.pt 128.45.233.7 192.26.12.1 192.26.1.30 128.45.233.6 surf.praia.pt stravinsky.ist.utl.pt 192.26.5.84 192.26.5.83 cromo.praia.pt ravel.ist.utl.pt Run nslookup

  24. Testing Internet destinations: the ping command ICMP Echo Reply ICMP Echo Request Run ping

  25. Discovering Internet routes: traceroute ICMP Echo Request ICMP Echo Request ICMP Echo Reply ICMP Time Exceeded ICMP Time Exceeded ICMP Echo Request Do a visual traceroute @ www.yougetsignal.com

  26. Internet crossing oceans

  27. Internet crossing oceans

  28. Internet paintings www.visualcomplexity.com

  29. Internet paintings www.visualcomplexity.com

  30. Internet paintings Convergence, JacksonPollock (1912-1956)

  31. Internet access Internet 24 Mbits/s 8X4X109 bits Download duration = 24X106 bits/s

  32. Internet access “The Cry”, Edvard Munch (1863-1944) Internet If after half an hour the download has not ended, what went wrong? 24 Mbits/s

  33. Internet access Internet If after half an hour the download has not ended, what went wrong? 2 Mbits/s server’s access network 24 Mbits/s

  34. Internet access 1 Mbits/s Internet If after half an hour the download has not ended, what went wrong? 24 Mbits/s server’s access network 24 Mbits/s

  35. Internet access: p2p 1 Mb/s 1 Mb/s 1 Mb/s 1 Mb/s Internet Internet 1 Mb/s 1 Mb/s 24 Mbits/s 24 Mbits/s

  36. 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 Packet-switching: store-and-forward L R R R more on delay shortly …

  37. Now break up the message into 5000 packets Packet Switching: Message Segmenting • Each packet 1,500 bits • 1 msec to transmit packet on one link • pipelining: each link works in parallel • Delay reduced from 15 sec to 5.002 sec

  38. Communication links Two types of “links”: • point-to-point • PPP for dial-up access • point-to-point link between Ethernet switch and host • broadcast (shared wire or medium) • old-fashioned Ethernet • upstream HFC • 802.11 wireless LAN humans at a cocktail party (shared air, acoustical) shared wire (e.g., cabled Ethernet) shared RF (e.g., 802.11 WiFi) shared RF (satellite)

  39. Communication links – antenna transmission systems

  40. Communication links – optical transmission systems

  41. Errors in communication links • Signal degrade due to: • Attenuation • Distortion • Noise • Interference

  42. What’s a protocol? Got the time? 2:00 time • a human protocol and a computer network protocol: Hi Hi Q: Other human protocols?

  43. What’s a protocol? • human protocols: • “what’s the time?” • “I have a question” • introductions • … specific msgs sent • … specific actions taken when msgs received, or other events • network protocols: • machines 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

  44. TFTP – an example of a network application protocol for file transfer • Internet standard defined in RFC (Request for Comment) by the IETF (Internet Engineering Task Force) • Includes an initial handshake • Files are segmented into messages • It is not efficient to transfer a large file in a single message • TFTP uses the Stop-and-Wait protocol for error control • Messages can be lost, corrupted or received out of order in the network • How is the end of a file transfer signaled?

  45. Stop-and-wait (SW) Operation without errors

  46. Stop-and-wait (SW) Error recovery

  47. Stop-and-wait (SW) DATA messages need to be numbered

  48. Stop-and-wait (SW) ACK messages need to be numbered

  49. Stop-and-wait (SW) Ok!

  50. TFTP message format ERROR CODE: 00 – Not defined 01 – File not found 02 – Access violation 03 – Disk full 04 – Invalid operation code 05 – Unknown port number06 – File already exists 07 – No such user

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