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Week 2 Application Layers ITEC 3210 Applied Data Communications and Networks Learning objectives • Application architecture – Overview – Operations – Best practices • Application exercises • Warning: – Application architecture ≠ network architecture – Cost of development is LOW for any architecture that uses off-the- shelf application software package (see slide 16) – Use of quotation marks when using “server” for non-C/S architectures (not in figures though!) – Other: see slides! ITEC 3210 Applied Data Communications and Networks Course overview ITEC 3210 Applied Data Communications and Networks Application architectures • Typical network application programs carry out four functions: – Data storage: Storage and retrieval of data – Data access logic: Query required to access a subset of data – Application logic: Work performed by application – Presentation logic: User interface • Three basic application architectures determine how these functions are split between clients and servers: – Host-based architecture – Client-based architecture – Client-server architecture • Application architecture: – Describes how application layer functions are spread among computers to deliver service to users – Not the same as network architecture which refers to a network physical and logical topology (hardware layer, see chapter 4) ITEC 3210 Applied Data Communications and Networks Host-based architecture • Very first application architecture to be developed – The host, usually a mainframe, performs all 4 application program functions – The “client”, usually a terminal or a PC running a terminal emulation program sends and receives messages to and from host (See figure 2.1) • Main limitation: – Upgrades come in large increments and are expensive Warning: Dennis writes that overload on host side can increase response time. This is true but it applies to ANY application architecture! • Typical applications: – Support main line of business in large “paper-based factories” such as banks, insurance companies, government agencies, hospitals, universities, etc. – Why? ITEC 3210 Applied Data Communications and Networks Host-based architecture ITEC 3210 Applied Data Communications and Networks Client-based architecture • AKA peer-to-peer architecture • Became important in the late 1980s with the widespread use of PCs and LANs – “Server” is a microcomputer responsible for data storage – “Client” is a microcomputer responsible for the data access, application and presentation logic (See figure 2-2) • Limitations: – No access logic on “server” side: All data must travel to client for processing since queries are performed by client Overload the network circuits poor network performance – “Server” is a microcomputer: Limited processing power on “server” side poor network performance ITEC 3210 Applied Data Communications and Networks Client-based architecture ITEC 3210 Applied Data Communications and Networks Client/Server architecture • Most common application architecture used in today’s networks – Server handles data storage and data access logic – Client takes care of the presentation logic – Application logic may reside on the client, server or be split up between the two (see next four slides) • Benefits: – Network performance: • Typically, servers have higher processing power • Processing is distributed between client and server – Lower required capacity (No unnecessary traffic) • Comes in different versions: See next slides ITEC 3210 Applied Data Communications and Networks Two-tier, three-tier and N-tier architectures Refers to ways the application logic is partitioned in C/S architecture • 2-tier architecture (see Figure 2-3): – 1 client, 1 server, application logic is “partitioned” between the 2 – Most common architecture when number of users is less than 50 • 3-tier architecture (see Figure 2-4): – The client handles the presentation logic – The application server handles the application logic – The database server handles the data storage and data access logic • N-tier architecture (see Figure 2-5): – More than three types of computers are used – Typically, a web server is added Easy access from anywhere – Major limitation: complexity ITEC 3210 Applied Data Communications and Networks Client/Server architecture (2-tier C/S architecture) ITEC 3210 Applied Data Communications and Networks Three-tier architecture ITEC 3210 Applied Data Communications and Networks N-tier architecture ITEC 3210 Applied Data Communications and Networks Thin versus thick clients • Refers to how much of the application logic resides on the client – Little or no application logic resides on a thin client – All or most of the application logic resides on a fat client • Thin clients are becoming popular because: – Systems are easier to manage: only the server application logic generally needs to be updated – Thin clients are cheaper ITEC 3210 Applied Data Communications and Networks More on clients and servers – http://www.serverwatch.com/ – Technical focus 2.1 p.34 – Assignment#1 ITEC 3210 Applied Data Communications and Networks Best practice architecture • Often, the application architecture is given. So no decision has to be made • When it is not given, 3 criteria help select an architecture: – Cost of Infrastructure: mainframes are expensive, which is why client-based and C/S architectures have become popular – Scalability refers to the ability to increase (or decrease) computing capacity as network demand changes. C/S architectures are the most scalable (both clients and servers can be added (reduced) to fit network requirements) – Cost of Development: Lower for ANY architecture that uses off-the-shelf software “For most projects, a C/S architecture, usually a three-tier thin or thick client, is recommended” p.41 ITEC 3210 Applied Data Communications and Networks Application exercise: More on C/S architecture Rate the C/S architecture on the criteria below: – Centralized data storage – Prevention of unauthorized access to file/applications – Reliability (built-in reliability) – Network administration – Performance (faster processing) – Number of users – Relative cost ITEC 3210 Applied Data Communications and Networks Application exercise Read minicase 2 p.60 –61: – Which C/S architecture would you suggest? – Why? Modular design: – Definition – Application in the context of minicase 2 ITEC 3210 Applied Data Communications and Networks Thank you ITEC 3210 Applied Data Communications and Networks
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