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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 Application Layer
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
Network Layers Computer 1 Computer 2 3
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
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
2.1 Hardware - Client • What the users use • PC • Terminal • Network Computers • Mobile Devices • Special Purpose 6
2.1 Hardware – Client (Special Purpose) Terminal Mobile Technologies Special Purpose 7
2.1 Hardware – Server • What the client accesses • PC (special purpose) • Mainframe • Clusters (aka Server Farms) • Special Purpose 8
2.1 Hardware – Server From 1970’s More Recent Mainframes 9
2.1 Hardware – Server Server Clusters Computer Cluster Clusters
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
2.2 Host (Server) Based Architecture CLIENT SERVER 12
2.2 Host Based Architecture Problems • Host becomes a bottleneck • Host upgrades typically expensive and “lumpy” 13
2.2 Client Based Architecture CLIENT SERVER 14
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
2.2 Client-Server Architecture CLIENT SERVER 2-Tier Architecture 16
2.2 Client-Server Architecture CLIENT SERVER 2-Tier Architecture
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
2.2 Client-Server Architecture • Advantages • Disadvantages 19
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
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
2.2 Client-Server Architecture CLIENT SERVER SERVER 22
2.2 Client-Server Architecture CLIENT SERVER SERVER SERVER 23
2.2 Client-Server Architecture (Multi-Tier) • Advantages • Disadvantages 24
Peer to Peer Architecture • All computers can serve as a client and a server • Advantages: • Disadvantages: 25
2.2 Criteria for Choosing Architecture Infrastructure Cost Development Cost Scalability 27
2.2 Choosing an Architecture Host-Based Client-Based Client-Server Cost of Infrastructure Cost of Development Scalability 28
2.3.1 Web (How it works) What happens when type a web address(2-Tier Networks, Client/Server) 29
2.3 Web HTTP Requests: Request Line Request Header Request Body 30
2.3 Web HTTP Response: Response Status Response Header Response Body 31
2.3 Web (Request/Response Demo) www.rexswain.com/httpview 32
2.4.1 Email (2-Tier - Thick Client) How a message is sent 33
2.4.1 Email (2-Tier - Thick Client) How a message is sent offsite (e.g. email from UNCW to UNC) 34
2.4.2 Email – Web Mail 3-Tier Email – Off Campus 35
2.4.3 Email – SMTP Packets Header Body 36
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
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
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
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
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