CS551End to End Argument[Saltzer81a]Bill Chenghttp://merlot.usc.edu/cs551-f121 Computer Communications - CSCI 551 Copyright © William C. Chenginside the network (in switching elements), orDeals with where to place protocol functionality (e.g.,encryption, reliability, ordering, duplication surpression):2The End-to-end Argument Computer Communications - CSCI 551 Copyright © William C. Chengat the edgesother architecture can use this principleNot an arhchitecture in itself, but an architectural principlee.g., architectures for transaction managementdon’t duplicate functionality in multiple levels if youhave to do it at the top anywayThe end-to-end argument3Key Ideas Computer Communications - CSCI 551 Copyright © William C. Chengbetter spend it on other thingsDuplicate functionality has a cost associated with itNeed to be general: Additional functionality may helpsome but may actually hurt other applicationsapply to networking: the lower layers of the network arenot the right place to implement application-specificfunctions (the lower network layers should implementbasic and general functions)move these functions up and outthe network should be as transparent as technologypermitswant an end-to-end checksum, even if network guaranteesreliable deliveryConsider copying a file4Example: Reliability Computer Communications - CSCI 551 Copyright © William C. ChengRecommendation: in order to achieve reliable file transfer,application program must supply a file-transfer-specific,end-to-end reliable guarantee (and not rely on the datacommunication system)A reads from disk to memory; sends over networkSteps:network moves data from A to BB gets data from network; writes to diskdisk I/O errors, buffer overruns in NIC, memory errors,network corruption or congestion, computer crashesPossible faults:Encrypted data transfer (cannot trust the network)5Other Examples Computer Communications - CSCI 551 Copyright © William C. ChengDuplicate message suppression (did I just double-click thebutton or single-clicked it?)Guaranteed FIFO message deliveryTransactions in a DBneed some physical redundancy (coding)Consider file copy again 6Caveat: Performance Computer Communications - CSCI 551 Copyright © William C. ChengReliability at physical, link, network, transport, applicationlayerssometimes want link repair (Ethernet retransmission aftercollision, wireless links)network level repair (TCP)application level checks (checksum)multiple levels may be needed for performance, notcorrectnessNATWhat breaks end2end connectivity?7End2End: A Broader View Computer Communications - CSCI 551 Copyright © William C. ChengWeb cachesTransparent web proxiesOthers?Is this bad and why?NAT - who’s talking?Web caches - web page out of date, server wants to keepa hit countTransparent web proxies - where are the ads? what elseis filtered out?me to my bank over HTTPS: browser to commerce serverConsider secure communication:8Difficulty: What Is the "End"? Computer Communications - CSCI 551 Copyright © William C. Chengme from home to USC over ssh: app-levelmy computer to USC over a virtual private network (VPN):network-layer on my computer to USC networkmy computer to the wireless base-station over 802.11with WEP: link-layer on my computer to wireless LANmy PIN number in my head to the ATM (?)but may increase risksLower-layers have benefits (wider coverage)rather a guideline that helps in application and protocoldesign analysisEnd-to-end argument is not an absolute rule (like Occam’srazor)9 Computer Communications - CSCI 551 Copyright © William C. Cheng Discussiondon’t put functionality inside the network when it wouldhave to be duplicated at the ends anywaySummarycame well before much of the Internet had been builtContextarguably the most influential paper in the history ofnetworkingImpactmeasure of worth: not many papers are remembered after20 yearshelpful for understanding the success of the Internetpeople tend to use it to justify/dispute everythingactive networks, sensor networks,
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