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CS536-2009-02-03

CS536-2009-02-03 - CS536 Application Layer Charles Killian...

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CS536: Application Layer Charles Killian Slides used from Kurose-Ross, Computer Networking, a Top Down Approach 2: Application Layer 1
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Announcements Programming assignment 1 Due Saturday, February 28 th , 2009, 11:59pm C++ STL is OK, JAVA is NOT Questions? Opt-in Discussion List See course webpage for details Sent email about rescheduling April 21,23 Don’t delay in responding First written assignment Expect it to come out later this week 2: Application Layer 2
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Recap: Application Layer Email SMTP POP, IMAP DNS Helper service Application no-one uses Quote once heard • “ DNS allows a computer on the far side of the world you weren’t trying to reach and never knew existed to prevent your computer from accessing resources in the next room” 2: Application Layer 3
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2: Application Layer 4 Chapter 2: Application layer 2.1 Principles of network applications app architectures app requirements 2.2 Web and HTTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P applications Programming network applications
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2: Application Layer 5 Pure P2P architecture no always-on server arbitrary end systems directly communicate peers are intermittently connected and change IP addresses Three topics: File distribution Searching for information Case Study: Skype peer-peer
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2: Application Layer 6 File Distribution: Server-Client vs P2P Question : How much time to distribute file from one server to N peers ? u s u 2 d 1 d 2 u 1 u N d N Server Network (with abundant bandwidth) File, size F u s : server upload bandwidth u i : peer i upload bandwidth d i : peer i download bandwidth
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2: Application Layer 7 File distribution time: server-client u s u 2 d 1 d 2 u 1 u N d N Server Network (with abundant bandwidth) F server sequentially sends N copies: NF/u s time client i takes F/d i time to download increases linearly in N (for large N) = d cs = max { NF/u s , F/min(d i ) } i Time to distribute F to N clients using client/server approach
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2: Application Layer 8 File distribution time: P2P u s u 2 d 1 d 2 u 1 u N d N Server Network (with abundant bandwidth) F server must send one copy: F /u s time client i takes F/d i time to download NF bits must be downloaded (aggregate) fastest possible upload rate: u s + Σ u i d P2P = max { F/u s , F/min(d i ) , NF/(u s + Σ u i ) } i
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2: Application Layer 9 Server-client vs. P2P: example Client upload rate = u, F/u = 1 hour, u s = 10u, d min u s
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2: Application Layer 10 File distribution: BitTorrent tracker: tracks peers participating in torrent torrent: group of peers exchanging chunks of a file obtain list of peers trading chunks peer P2P file distribution
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