CS536-2009-01-27

CS536-2009-01-27 - 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 PSO Changes Camille and Zhen have swapped times/days Programming assignment 1 Due Saturday, February 28 th , 2009, 11:59pm C++ STL is OK JAVA is NOT Opt-in Discussion List See course webpage for details 2: Application Layer 2
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Recap: HTTP Request Response Response Codes Stateless Protocols 2: Application Layer 3
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2: Application Layer 4 Chapter 2: Application layer 2.1 Principles of network applications 2.2 Web and HTTP 2.3 FTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P applications 2.7 Socket programming with TCP 2.8 Socket programming with UDP
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2: Application Layer 5 User-server state: cookies Many major Web sites use cookies Four components: 1) cookie header line of HTTP response message 2) cookie header line in HTTP request message 3) cookie file kept on user’s host, managed by user’s browser 4) back-end database at Web site Example: Susan always access Internet always from PC visits specific e- commerce site for first time when initial HTTP requests arrives at site, site creates: unique ID entry in backend database for ID
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2: Application Layer 6 Cookies: keeping “state” (cont.) client server usual http response msg usual http response msg cookie file one week later: usual http request msg cookie: 1678 cookie- specific action access ebay 8734 usual http request msg Amazon server creates ID 1678 for user create entry usual http response Set-cookie: 1678 ebay 8734 amazon 1678 usual http request msg cookie: 1678 cookie- spectific action access ebay 8734 amazon 1678 backend database
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2: Application Layer 7 Cookies (continued) What cookies can bring: authorization shopping carts recommendations user session state (Web e-mail) Cookies and privacy: cookies permit sites to learn a lot about you you may supply name and e-mail to sites aside How to keep “state”: protocol endpoints: maintain state at sender/receiver over multiple transactions cookies: http messages carry state
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Cookies (continued) Doubleclick.net Google-analytics Com.com Traffic Aggregate Analysis Consumer Profiles 2: Application Layer 8
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2: Application Layer 9 Web caches (proxy server) user sets browser: Web accesses via cache browser sends all HTTP requests to cache object in cache: cache returns object else cache requests object from origin server, then returns object to client Goal: satisfy client request without involving origin server client Proxy server client origin server origin server
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2: Application Layer 10 More about Web caching cache acts as both client and server typically cache is installed by ISP (university, company, residential ISP) Why Web caching? reduce response time
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CS536-2009-01-27 - CS536: Application Layer Charles Killian...

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