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CHAPTER 2

CHAPTER 2. Application Layer. Announcements and Outline. Administrative Items Questions? Recap Introduction to Networks Network Type N etwork Layers Today’s Outline Application Layer 2.1 Hardware 2.2 Application Architecture (Software) 2.3 Web 2.4 Email. 2. Network Layers.

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CHAPTER 2

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  1. CHAPTER 2 Application Layer

  2. Announcements and Outline • Administrative Items • Questions? Recap • Introduction to Networks • Network Type • Network Layers Today’s Outline • Application Layer 2.1 Hardware 2.2 Application Architecture (Software) 2.3 Web 2.4 Email 2

  3. Network Layers Computer 1 Computer 2 3

  4. Acronyms of the Day • HTTP – Hypertext Transfer Protocol • SMTP – Simple Mail Transfer Protocol • POP – Post Office Protocol • IMAP – Internet Message Access Protocol • MIME – Multipurpose Internet Mail Extensions 4

  5. 2 Application Layer Applications (e.g., email, web, word processing) Application Layer Transport Layer Network Layer • The software that enables the user to perform useful work • Application architecture • The way in which the functions of the application layer software are spread among the clients and servers on the network • Functions of Application Layer 5

  6. 2.1 Hardware - Client • What the users use • PC • Terminal • Network Computers • Mobile Devices • Special Purpose 6

  7. 2.1 Hardware – Client (Special Purpose) Terminal Mobile Technologies Special Purpose 7

  8. 2.1 Hardware – Server • What the client accesses • PC (special purpose) • Mainframe • Clusters (aka Server Farms) • Special Purpose 8

  9. 2.1 Hardware – Server From 1970’s More Recent Mainframes 9

  10. 2.1 Hardware – Server Server Clusters Computer Cluster Clusters

  11. 2.2 Application Architecture • Splitting the work across the client and the server • Basic Software Components: • Presentation Logic • Application Logic • Data Access Logic • Data 11

  12. 2.2 Host (Server) Based Architecture CLIENT SERVER 12

  13. 2.2 Host Based Architecture Problems • Host becomes a bottleneck • Host upgrades typically expensive and “lumpy” 13

  14. 2.2 Client Based Architecture CLIENT SERVER 14

  15. 2.2 Client Based Architecture Problems • Data traffic must travel back and forth between server and client • Example: when the client program is making a database query, the ENTIRE database must travel to the client before the query can be processed • Often the large file sizes moving across the LAN can yield a poor result in network performance 15

  16. 2.2 Client-Server Architecture CLIENT SERVER 2-Tier Architecture 16

  17. 2.2 Client-Server Architecture CLIENT SERVER 2-Tier Architecture

  18. Thin and Thick Clients • Classification depends on how much of the application logic resides on the client or server • Thin client: • Little or no application logic on client • Becoming popular because easier to manage, (only the server application logic generally needs to be updated) • The best example: World Wide Web architecture (uses a two-tier, thin client architecture) • Thick client: • All or most of the application logic resides on the client

  19. 2.2 Client-Server Architecture • Advantages • Disadvantages 19

  20. Examples of standards for Middleware: Distributed Computing Environment (DCE) Common Object Request Broker Architecture (CORBA) Open Database Connectivity (ODBC) Middleware client application programs a standard way of translating between software from different vendors • Manages message transfers • Insulates network changes from the clients (e.g., adding a new server) Middleware server application programs 20

  21. Multi-tier Architectures • Involve more than two computers in distributing application program logic • 2-tier architecture • Uses clients and servers in a balance, very popular approach in simple LANs • 3-tier architecture • 3 sets of computers involved • N-tier architecture • More than three sets of computers used, more typical across complex organizations • Allows load balancing across servers 21

  22. 2.2 Client-Server Architecture CLIENT SERVER SERVER 22

  23. 2.2 Client-Server Architecture CLIENT SERVER SERVER SERVER 23

  24. 2.2 Client-Server Architecture (Multi-Tier) • Advantages • Disadvantages 24

  25. Peer to Peer Architecture • All computers can serve as a client and a server • Advantages: • Disadvantages: 25

  26. Peer to Peer Architecture 26

  27. 2.2 Criteria for Choosing Architecture Infrastructure Cost Development Cost Scalability 27

  28. 2.2 Choosing an Architecture Host-Based Client-Based Client-Server Cost of Infrastructure Cost of Development Scalability 28

  29. 2.3.1 Web (How it works) What happens when type a web address(2-Tier Networks, Client/Server) 29

  30. 2.3 Web HTTP Requests: Request Line Request Header Request Body 30

  31. 2.3 Web HTTP Response: Response Status Response Header Response Body 31

  32. 2.3 Web (Request/Response Demo) www.rexswain.com/httpview 32

  33. 2.4.1 Email (2-Tier - Thick Client) How a message is sent 33

  34. 2.4.1 Email (2-Tier - Thick Client) How a message is sent offsite (e.g. email from UNCW to UNC) 34

  35. 2.4.2 Email – Web Mail 3-Tier Email – Off Campus 35

  36. 2.4.3 Email – SMTP Packets Header Body 36

  37. 2.4.4 Email – Sending Attachments • SMTP is a relatively old protocol and is text only, so how do we send attachments using text only? • MIME (Multipurpose Internet Mail Extension) MIME example 37

  38. Instant Messaging (IM) • A client-server program that allows real-time typed messages to be exchanged • Client needs an IM client software • Server needs an IM server package • Some types allow voice and video packets to be sent • Like a telephone • Examples include AOL and ICQ • Two step process: • Telling IM server that you are online • Chatting

  39. How Instant Messaging Works

  40. Videoconferencing • Provides real time transmission of video and audio signals between two or more locations • Allows people to meet at the same time in different locations • Saves money and time by not having to move people around • Typically involves matched special purpose rooms with cameras and displays • Desktop videoconferencing • Low cost application linking small video cameras and microphones together over the Internet • No need for special rooms • Example: Net Meeting software on clients communicating through a common videoconference server

  41. Recap – Application Layer 2.1 Hardware 2.1.1 Clients 2.1.2 Servers 2.2 Application Architecture (Software) 2.3 Web 2.3.1 How it works 2.3.2 Requests and Responses 2.4 Email 2.4.1 How it Works 2.4.2 Requests and Sending Attachments 41

  42. Next Class • Read Chapter 3 - Physical Layer • Find out what service you currently use • What are the transmission speed? • What type of transmissions are utilized – Analog or Digital? 42

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