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Networked Applications Chapter 11 Updated January 2009 Raymond Panko’s Business Data Networks and Telecommunications, 7th edition May only be used by adopters of the book © 2009 Pearson Education, Inc. Publishing as Prentice Hall Client/Server Computing • The client does at least some of the work Server Program Client Program Server Client PC © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-2 11-2: Client/Server Computing 3 Client/Server Processing with Request-Response Cycle Request Message Client Program Response Message Does Light I/O and Post-Download Processing Client PC Server Program Does Heavy Database and Other Heavy Processing File Server Use larger server as number of clients increases © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-3 11-3: Web-Enabled Application HTTP Request Message Client is Browser Client PC HTTP Response Message Server Program 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. E-Mail Server © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-4 E-Mail © 2009 Pearson Education, Inc. Publishing as Prentice Hall The E-Mail Delivery Process Sender’s Mail Server Receiver’s Mail Server Each e-mail user has a mail server. Sending E-Mail Client The sender transmits a message to its mail server. Receiving The sender’s mail server delivers the message E-Mail to the receiver’s mail server. Client The receiver’s mail server delivers the message to the receiver. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-6 11-5: E-Mail Standards: Sending 2. SMTP To Send 1. SMTP To Send Sender’s Mail Server Sending E-Mail Client (Outlook, etc.) Receiver’s Mail Server Simple Mail Transfer Protocol (SMTP) is used to transmit mail in real time to a user’s mail server or between mail servers Receiving E-Mail Client (Outlook, etc.) Sender-initiated Note that SMTP provides immediate delivery—usually in a few seconds. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-7 11-5: E-Mail Standards: Receiving 3. POP or IMAP to Receive Sender’s Mail Server Sending E-Mail Client (Outlook, etc.) Receiver’s Mail Server POP or IMAP to download mail to receiver when the receiver next downloads mail Receiving E-Mail Client (Outlook, etc.) Receiver-initiated © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-8 11-5: E-Mail Standards: Web-Based E-Mail SMTP HTTP SMTP POP or IMAP Traditional E-Mail Client (Outlook, etc.) 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. Web-Based E-Mail Client Browser Server-server communication always uses SMTP. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-9 HTML and HTTP © 2009 Pearson Education, Inc. Publishing as Prentice Hall 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 © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-11 E-Commerce © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-10: Electronic Commerce Functions Browser Webserver Application E-Commerce Server Customer PC External Database © 2009 Pearson Education, Inc. Publishing as Prentice Hall Internal Database 11-13 11-10: EC Functions • Webserver Functionality, Plus… • E-Commerce functionality – Online catalog – Shopping cart – Checkout, including payment – Customer resource management (CRM) – Links to External Systems • Credit card number checking © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-14 11-10: EC Functions • E-Commerce functionality – Links to internal systems • Accounting • Pricing • Warehousing (product availability) • Shipment • Etc. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-15 Three-Tier Architecture presentation tier web browser logic tier web server and programs • Three-tier model is a software architecture •Data transfer between tiers is part of the architecture © 2009 Pearson Education, Inc. Publishing as Prentice Hall data tier database/ file system Three-Tier Architecture Presentation Business Logic Web browser Payment User/Admin Content Modules Data Database © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-11: Application Server (3-Tier Architecture) Client PC with Browser 1. Form Webserver Application 2. Server Data Mainframe 1. User fills in a form using a browser 2. Webserver sends form data onto an application server Server of External Company © 2009 Pearson Education, Inc. Publishing as Prentice Hall Database Server 11-18 11-11: Application Server (3-Tier Architecture) Client PC with Browser Webserver 3. Mainframe Query and Application Response Server Mainframe 3. To get data needed to serve the customer, the application server queries a mainframe database and reads the information in the response Database Server Server of External Company © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-19 11-11: Application Server (3-Tier Architecture) Client PC with Browser Webserver Application Server 4. DB Server Mainframe Query and Response 5. External Query/ Response Database Sever Interactions (4, 5) Application program interfaces (API) Both internal and external database hosts Database Server Server of External Company © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-20 11-11: Application Server (3-Tier Architecture) Client PC with Browser 7. Webpage Webserver Application Server 6. New Webpage 6. From the retrieved data, the Application Server creates a new webpage 7. Webserver sends Mainframe the webpage to the browser Server of External Company © 2009 Pearson Education, Inc. Publishing as Prentice Hall Database Server 11-21 Peer-to-Peer Computing © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-15: Traditional Client/Server Application Client PC Client PC Advantage: Central Control Client PC Client PC Client PC Disadvantages: Network Overload at Server Underused Client Power Central Control Server Does Heavy Processing Work © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-23 P2P Applications • Direct service, although most P2P systems use facilitating servers for some of the work Peer Peer Peer Peer Peer Peer © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-24 Figure 11-16: Simple Peer-to-Peer (P2P) Application Request Client PC Response Benefits: End User Freedom No Network Bottleneck at Server Uses Client Capacity Better Client PC Problems: Transient Presence of Clients Transient Client IP Addresses Security (No Central Control) © 2009 Pearson Education, Inc. Publishing as Prentice Hall 11-25