CS536-2009-01-29

CS536-2009-01-29 - 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 Expect email about rescheduling April 21,23 2: Application Layer 2
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Recap: Application Layer Understanding applications by example Protocol in RFCs HTTP FTP SMTP Text-based 1 or 2 sockets Client-server 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 Electronic Mail Three major components: user agents mail servers simple mail transfer protocol: SMTP User Agent a.k.a. “mail reader” composing, editing, reading mail messages e.g., Eudora, Outlook, elm, Mozilla Thunderbird outgoing, incoming messages stored on server user mailbox outgoing message queue mail server user agent user agent user agent mail server user agent user agent mail server user agent SMTP SMTP SMTP
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2: Application Layer 6 Electronic Mail: mail servers Mail Servers mailbox contains incoming messages for user message queue of outgoing (to be sent) mail messages SMTP protocol between mail servers to send email messages client: sending mail server “server”: receiving mail server mail server user agent user agent user agent mail server user agent user agent mail server user agent SMTP SMTP SMTP
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2: Application Layer 7 Electronic Mail: SMTP [RFC 2821] uses TCP to reliably transfer email message from client to server, port 25 direct transfer: sending server to receiving server three phases of transfer handshaking (greeting) transfer of messages closure command/response interaction commands: ASCII text response: status code and phrase messages must be in 7-bit ASCII
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2: Application Layer 8 Scenario: Alice sends message to Bob 1) Alice uses UA to compose message and “to” bob@someschool.edu 2) Alice’s UA sends message to her mail server; message placed in message queue 3) Client side of SMTP opens TCP connection with Bob’s mail server 4) SMTP client sends Alice’s message over the TCP connection 5) Bob’s mail server places the message in Bob’s mailbox 6) Bob invokes his user agent to read message user agent mail server mail server user agent 1 2 3 4 5 6
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9 Sample SMTP interaction S: 220 hamburger.edu C: HELO crepes.fr S: 250 Hello crepes.fr, pleased to meet you C: MAIL FROM: <alice@crepes.fr> S: 250 alice@crepes.fr. .. Sender ok C: RCPT TO: <bob@hamburger.edu> S: 250 bob@hamburger.edu . .. Recipient ok C: DATA S: 354 Enter mail, end with "." on a line by itself
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CS536-2009-01-29 - CS536: Application Layer Charles Killian...

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