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Lecture 1: Design Principles of the Internet
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Lecture 1: Design Principles of the Internet Lecture 1: Design Principles of the Internet Presentation Transcript

  • David D. Clark’s paper" “The Design Philosophy of the DARPA Internet Protocols” 1988! 14 August 2009! CS5229 Semester 1, 2009/10! 1!
  • 14 August 2009! CS5229 Semester 1, 2009/10! 2!
  • Why the Internet is " the way it is?! 14 August 2009! CS5229 Semester 1, 2009/10! 3!
  • In the beginning..! 14 August 2009! CS5229 Semester 1, 2009/10! 4!
  • Need a communication network that will survive a war:" multipath between two hosts" divide messages into message blocks" deliver the message blocks using store- and-forward switching ! 14 August 2009! CS5229 Semester 1, 2009/10! 5!
  • http://www.rand.org/pubs/research_memoranda/RM3420/RM3420.chapter1.html! 14 August 2009! CS5229 Semester 1, 2009/10! 6!
  • ARPANET! host! host! packet switch! network over! phone lines! host! 14 August 2009! CS5229 Semester 1, 2009/10! 7!
  • ARPANET! From “An Atlas of Cyberspace”, A website by Martin Dodge! 14 August 2009! CS5229 Semester 1, 2009/10! 8!
  • “Come and write applications using our network!”! 14 August 2009! CS5229 Semester 1, 2009/10! 9!
  • Wait, we need to write our own packet switching software??! 14 August 2009! CS5229 Semester 1, 2009/10! 10!
  • Interface Message Processors (IMP)! IMP! IMP! packet switch! network over ! IMP! phone lines! 14 August 2009! CS5229 Semester 1, 2009/10! 11!
  • 14 August 2009! CS5229 Semester 1, 2009/10! 12! http://www.webstart.com/jed/service/vs-bbn-imp.jpg!
  • Services of IMP:" segmentation: break into 1Kb blocks" header: add header" routing" reliability: ACK, checksum" reassembly" flow control! 14 August 2009! CS5229 Semester 1, 2009/10! 13!
  • telnet! ftp! IMP! IMP! ftp! telnet! IMP! ftp! telnet! 14 August 2009! CS5229 Semester 1, 2009/10! 14!
  • Both applications need to establish connections! 14 August 2009! CS5229 Semester 1, 2009/10! 15!
  • Network Control Program! telnet! ftp! IMP! IMP! ftp! telnet! IMP! ftp! telnet! 14 August 2009! CS5229 Semester 1, 2009/10! 16!
  • Meanwhile.." PRNET" SATNET" being developed! 14 August 2009! CS5229 Semester 1, 2009/10! 17!
  • How to make disjoint networks talk to each other effectively ? ! 14 August 2009! CS5229 Semester 1, 2009/10! 18!
  • Choices! A.! Build a tightly integrated, unified network! B.! Interconnect existing network! 14 August 2009! CS5229 Semester 1, 2009/10! 19!
  • Why ?! More practical. Networks represent separately administered entities.! 14 August 2009! CS5229 Semester 1, 2009/10! 20!
  • Choices! A.! Packet Switching! B.! Circuit Switching! 14 August 2009! CS5229 Semester 1, 2009/10! 21!
  • Why ?! The networks to be integrated are packet switched network. Packet switch is natural choice for the applications at the time (remote login).! 14 August 2009! CS5229 Semester 1, 2009/10! 22!
  • 14 August 2009! CS5229 Semester 1, 2009/10! 23!
  • But, NCP assumes reliable network layer (IMP), PRNET is not reliable.! 14 August 2009! CS5229 Semester 1, 2009/10! 24!
  • Cerf & Kahn:! What’s the best design for an NCP replacement? ! How should the network be attached to each other?! 14 August 2009! CS5229 Semester 1, 2009/10! 25!
  • TCP replaces NCP! 14 August 2009! CS5229 Semester 1, 2009/10! 26!
  • Cerf & Kahn:! What’s the best design for an NCP replacement? ! How should the network be attached to each other?! 14 August 2009! CS5229 Semester 1, 2009/10! 27!
  • Introduces! Gateways! Addresses! IP! 14 August 2009! CS5229 Semester 1, 2009/10! 28!
  • Goals! Robust - work despite failure of networks or gateways! Versatile - support a variety of services and networks! Permit distributed management of resources! Cost effective ! Easy to add new hosts! Permit accounting of resources ! 14 August 2009! CS5229 Semester 1, 2009/10! 29!
  • Goal! “Survivability in the Face of Failure”! Communication between two entities should ! continue after temporary disruption without ! needing to reestablish connection states.! Or! Mask transient failure! 14 August 2009! CS5229 Semester 1, 2009/10! 30!
  • Store connection states in! A.! packet switching nodes! B.! end nodes! 14 August 2009! CS5229 Semester 1, 2009/10! 31!
  • Why ?! Easier to implement than replication. Replication only protects against finite number of node failures.! 14 August 2009! CS5229 Semester 1, 2009/10! 32!
  • “Fate-Sharing”! The only way the states are lost is the failure of end hosts.! 14 August 2009! CS5229 Semester 1, 2009/10! 33!
  • Consequences! Stateless packet switchers.! Need to trust end hosts.! 14 August 2009! CS5229 Semester 1, 2009/10! 34!
  • Need to support ! a variety of services! 14 August 2009! CS5229 Semester 1, 2009/10! 35!
  • Services! Remote login - low delay, reliable! File transfer - delay not important, reliable! Teleconferencing - reliability not important, low delay! 14 August 2009! CS5229 Semester 1, 2009/10! 36!
  • Choice! A.! Introduces UDP.! 14 August 2009! CS5229 Semester 1, 2009/10! 37!
  • Protocols! IP - datagram-based, best effort! TCP - reliable service over IP! UDP - unreliable service over IP ! 14 August 2009! CS5229 Semester 1, 2009/10! 38!
  • Compared to! X.25 - provides reliable services (that cannot be switched off!) ! 14 August 2009! CS5229 Semester 1, 2009/10! 39!
  • Need to support ! a variety of networks! 14 August 2009! CS5229 Semester 1, 2009/10! 40!
  • Make minimal assumptions! Can transport packets! Best effort delivery! Addressing! Minimum packet size! 14 August 2009! CS5229 Semester 1, 2009/10! 41!
  • Not assuming! Reliability! Ordered delivery! Packet prioritization! Broadcast/multicast! Knowledge of network stats! 14 August 2009! CS5229 Semester 1, 2009/10! 42!
  • Application-driven! TCP designed for dominant application at the time -- telnet! e.g. stream-oriented seq no! 14 August 2009! CS5229 Semester 1, 2009/10! 44!
  • David D. Clark’s paper" “The Design Philosophy of the DARPA Internet Protocols” 1988! 14 August 2009! CS5229 Semester 1, 2009/10! 45!
  • Another David D. Clark’s paper" “End-to-End Arguments in System Design” 1984" (with Saltzer and Reed)! 14 August 2009! CS5229 Semester 1, 2009/10! 46!
  • E2E Argument! A tool to guide designers: which layer to implement a given functionality?! 14 August 2009! CS5229 Semester 1, 2009/10! 47!
  • Example! Reliable file transfer between host A and host B! 14 August 2009! CS5229 Semester 1, 2009/10! 48!
  • Steps! 1. A reads file from disk! 2. A transmits file as packets! 3. Network delivers packets! 4. B receives packets! 5. B write data to disk! 14 August 2009! CS5229 Semester 1, 2009/10! 49!
  • Possible Errors! 1. Disk fault! 2. Software bugs! 3. Packet loss! 4. Processor/Memory errors! 5. OS crashes! 14 August 2009! CS5229 Semester 1, 2009/10! 50!
  • Choices! A.! Make sure every step is reliable! B.! End-to-end check and retry (compare checksum, resend if error)! 14 August 2009! CS5229 Semester 1, 2009/10! 51!
  • The Argument! To achieve careful file transfer, the transfer application must apply application-specific, end-to-end reliability guarantee.! 14 August 2009! CS5229 Semester 1, 2009/10! 52!
  • The Argument! “! The end-to-end check of the file transfer application must still be implemented no matter how ”! reliable the communication system becomes.! 14 August 2009! CS5229 Semester 1, 2009/10! 53!
  • Conclusion! No need to provide reliability guarantee at lower level (e.g. network, OS, hardware)! 14 August 2009! CS5229 Semester 1, 2009/10! 54!
  • Actually,! Lower level reliability can improve performance. ! 14 August 2009! CS5229 Semester 1, 2009/10! 55!
  • To implement at low- level?! Additional cost for applications that do not require the feature.! Less information than the “end”, less efficient. ! 14 August 2009! CS5229 Semester 1, 2009/10! 56!
  • Other Example:! Data Encryption! 14 August 2009! CS5229 Semester 1, 2009/10! 57!
  • Choices! A.! Encrypt at the network- level! B.! Encrypt in the application! 14 August 2009! CS5229 Semester 1, 2009/10! 58!
  • Why?! Intercept before reaching the network! Need to trust the network! Still need to authenticate! 14 August 2009! CS5229 Semester 1, 2009/10! 59!
  • Other Example:! Duplicate Messages! 14 August 2009! CS5229 Semester 1, 2009/10! 60!
  • Other Example:! Delivery Guarantees! 14 August 2009! CS5229 Semester 1, 2009/10! 61!
  • Other Example:! RISC! 14 August 2009! CS5229 Semester 1, 2009/10! 62!
  • Other Example:! Recovery in ! Telephony Exchange! 14 August 2009! CS5229 Semester 1, 2009/10! 63!
  • The Argument! Any attempt by the computer designer to anticipate the client’s requirements will probably miss the target and the client will end up re-implementing it anyway.! 14 August 2009! CS5229 Semester 1, 2009/10! 64!
  • The End Point?! 14 August 2009! CS5229 Semester 1, 2009/10! 65!
  • Applications?! Users?! Hosts?! 14 August 2009! CS5229 Semester 1, 2009/10! 66!
  • The end-point is a trustworthy entity.! 14 August 2009! CS5229 Semester 1, 2009/10! 67!
  • Example! Reliable file transfer between host A and host B! 14 August 2009! CS5229 Semester 1, 2009/10! 68!
  • If I don’t trust the file transfer application, I need to check for error myself.! 14 August 2009! CS5229 Semester 1, 2009/10! 69!
  • E2E Argument! “! The function in question can completely and correctly be implemented only with the knowledge and help of the application standing at the endpoints of the communication system. Therefore, providing the questioned function as a feature of the communication system itself is not possible. (Sometimes an incomplete version of ”! the function provided by the communication system may be useful as a performance enhancement)! 14 August 2009! CS5229 Semester 1, 2009/10! 70!