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2009 Pearson Education, Inc. Publishing as Prentice Hall Networked Applications Chapter 11 Updated January 2009 Raymond Pankos Business Data Networks and Telecommunications, 7th edition May only be used by adopters of the book

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2009 Pearson Education, Inc. Publishing as Prentice Hall 11-2 Client/Server Computing The client does at least some of the work Server Client PC Client ProgramServer Program

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2009 Pearson Education, Inc. Publishing as Prentice Hall 11-3 11-2: Client/Server Computing File Server Client PC Use larger server as number of clients increases Client/Server Processing with Request-Response Cycle Client ProgramServer Program Request Message Response Message Does Light I/O and Post-Download Processing Does Heavy Database and Other Heavy Processing 3

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2009 Pearson Education, Inc. Publishing as Prentice Hall 11-4 11-3: Web-Enabled Application E-Mail Server Client PC Client is BrowserServer Program HTTP Request Message HTTP Response Message Web-enabled applications: Form of client server processing that uses browsers as clients. Almost all client PCs now have browsers. No need to install new software.

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2009 Pearson Education, Inc. Publishing as Prentice Hall E-Mail

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2009 Pearson Education, Inc. Publishing as Prentice Hall 11-6 Each e-mail user has a mail server. The sender transmits a message to its mail server. The senders mail server delivers the message to the receivers mail server. The receivers mail server delivers the message to the receiver. Each e-mail user has a mail server. The sender transmits a message to its mail server. The senders mail server delivers the message to the receivers mail server. The receivers mail server delivers the message to the receiver. The E-Mail Delivery Process Sending E-Mail Client Receiving E-Mail Client Senders Mail Server Receivers Mail Server

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2009 Pearson Education, Inc. Publishing as Prentice Hall 11-7 11-5: E-Mail Standards: Sending 2. SMTP To Send 1. SMTP To Send Sending E-Mail Client (Outlook, etc.) Receiving E-Mail Client (Outlook, etc.) Senders Mail Server Receivers Mail Server Simple Mail Transfer Protocol (SMTP) is used to transmit mail in real time to a users mail server or between mail servers Sender-initiated Note that SMTP provides immediate deliveryusually in a few seconds.

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2009 Pearson Education, Inc. Publishing as Prentice Hall 11-8 11-5: E-Mail Standards: Receiving Senders Mail Server Receivers Mail Server 3. POP or IMAP to Receive POP or IMAP to download mail to receiver when the receiver next downloads mail Receiver-initiated Sending E-Mail Client (Outlook, etc.) Receiving E-Mail Client (Outlook, etc.)

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2009 Pearson Education, Inc. Publishing as Prentice Hall 11-9 On the left, we have just seen that traditional e-mail clients send with SMTP and receive with POP or IMAP. On the right, Web-based e-mail clients only need a browser and use HTTP both to send and to receive. Server-server communication always uses SMTP. On the left, we have just seen that traditional e-mail clients send with SMTP and receive with POP or IMAP. On the right, Web-based e-mail clients only need a browser and use HTTP both to send and to receive. Server-server communication always uses SMTP. 11-5: E-Mail Standards: Web-Based E-Mail Traditional E-Mail Client (Outlook, etc.) Web-Based E-Mail Client Browser SMTP POP or IMAP HTTP SMTP

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2009 Pearson Education, Inc. Publishing as Prentice Hall HTML and HTTP

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2009 Pearson Education, Inc. Publishing as Prentice Hall 11-11 11-7: HTML and HTTP The Hypertext Transfer Protocol (HTTP) is the standard for transferring messages between the client (browser) and the server (webserver). The Hypertext Markup Language (HTML) is a standard for text documents that have tags to indicate formatting and other files to be downloaded

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2009 Pearson Education, Inc. Publishing as Prentice Hall Peer-to-Peer Computing

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2009 Pearson Education, Inc. Publishing as Prentice Hall 11-13 11-15: Traditional Client/Server Application Client PC Server Does Heavy Processing Work Disadvantages: Network Overload at Server Underused Client Power Central Control Advantage: Central Control

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2009 Pearson Education, Inc. Publishing as Prentice Hall 11-14 P2P Applications Direct service, although most P2P systems use facilitating servers for some of the work Peer

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2009 Pearson Education, Inc. Publishing as Prentice Hall 11-15 Figure 11-16: Simple Peer-to-Peer (P2P) Application Client PC Request Response Benefits: End User Freedom No Network Bottleneck at Server Uses Client Capacity Better Problems: Transient Presence of Clients Transient Client IP Addresses Security (No Central Control)