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Journey to the Center of the Internet

Journey to the Center of the Internet. John Kristoff jtk@depaul.edu +1 312 362-5878 DePaul University Chicago, IL 60604. Internet as a layered architecture. Application layer Web, email Transport layer Reliability, flow control Internet layer Routing, global addressing Link layer

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Journey to the Center of the Internet

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  1. Journey to the Center of the Internet • John Kristoff • jtk@depaul.edu • +1 312 362-5878 • DePaul University • Chicago, IL 60604

  2. Internet as a layered architecture • Application layer • Web, email • Transport layer • Reliability, flow control • Internet layer • Routing, global addressing • Link layer • Ethernet, PPP • Physical layer • Wires, radio, optical fiber

  3. Meet Ms. Dana Paquette • She has a high-speed Internet connection • She's browsing the web • She just clicked on a web link • Let's watch...

  4. Take me to www.isoc.org • Web site clicked is www.isoc.org • IP doesn't understand names • We must convert this to an IP address • TCP/IP software to DNS server: • "What is the IP address of www.isoc.org?" • DNS server replies: • "www.isoc.org = 206.131.249.182"

  5. Protocol stack, connect()! • Create destination TCP/IP packet using: • Destination host = 206.131.249.182 • Destination application = http (port 80) • Fill in source host information • Source IP address • Source application number • Other info (we'll return to specifics later) • Send connection request

  6. TCP/IP sends packet to adapter

  7. Ethernet card encapsulates data • Could be wireless, FDDI, cable modem, etc. • TCP/IP packet goes into payload • Ethernet dest. address = gateway router

  8. Out the card, onto the wire...

  9. Bit by bit...

  10. Into the walls and ceilings...

  11. Through the patch panel...

  12. Onto the Ethernet switch...

  13. To the campus router... • Peels off layer 2 info • Router performs lookup for IP dest. • Forwards towards destination network • Decrements time to live field • Re-computes IP checksum

  14. And out the Internet router...

  15. To the Internet towards ISOC.org!

  16. IP ties everything together • IP carries data end-to-end across links • Routers examine IP layer information • They forward towards the destination • Similar to the sorting process of postal service • Identifies both a source and destination • Unreliable - no guaranteed delivery! • Primary role of IP: to move packets around

  17. The IP datagram

  18. The case for reliability • Sometimes the network is offered more packets than it can handle • Can't queue forever • Might prefer to drop packets rather than delay them • Sender can easily re-send packets • Need a protocol to ensure reliability • The case for TCP! • Note: reliability is placed in the hands of end-points • We'll come back to this in a minute

  19. Congestion control and avoidance • TCP increases transmission rate over time • If TCP detects a packet loss it slows down • Competing TCPs lead to fairness over time

  20. The TCP segment

  21. The end-to-end picture

  22. Dana to ISOC.org TCP/IP packet

  23. End-to-end principle • Guiding principle of the Internet architecture • Considers where to put intelligence • Minimize functions and features within the communcations system • Need end-to-end functions anyway • Argues against fate-sharing and network statefulness

  24. Is the Internet broken? • E2E is being violated as standard practice • Network address translation (NAT) • Firewalls • Various middleboxes • New applications are difficult to deploy • IPv6 could shift move back towards E2E • Architecture has probably changed forever • ...won't come all the way back

  25. Anything else wrong with the 'net? • Security, security and security • There will continue to be major issues here • Internet is based on trust relationships • Host security is hard, net security doesn't work • Routing table growth • Not a critical problem, but causing some concern • Increase in multi-homing casing table bloat

  26. What's new and exciting?(or "the I finished too early slide") • Wireless • Interactive applications • Voice and games • IPv6 • DNS • High-speed technologies and testbeds

  27. References • http://www.reed.com/Papers/EndtoEnd.html • http://www.ietf.org • RFC 2775 Internet Transparency • RFC 1958 Architectural Principles of the Internet • http://www.nanog.org • http://networks.depaul.edu • http://condor.depaul.edu/~jkristof/

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