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Networking IS589 Concepts and Applications Homework week 1 October 26, 2010 Ch 1: Question 13 13. Describe the five layers in the Internet network model and what they do. Layer Application Layer Transport Layer Purpose Used by application program. It is the users access to the network. By using the application software, the user defines what messages are sent over the network. Responsible for establishing end-to-end connections, translates domain names into numeric addresses, segments messages and detect lost messages and request that they be resent. Responsible for end-to-end addressing and routing, determines destination address if unknown. Deals with message delineation, error control and network medium access control . Is the physical connection between the sender and receiver, defines how individual bits are formatted to be transmitted through the network. Its role is to transfer a series of electrical, radio, or light signals through the circuit. The physical layer includes all the hardware devices (e.g., computers, modems, and hubs) and physical media (e.g., cables and satellites). Network Layer Data Link Layer Physical Layer Ch 2: Question 7 7. Compare and contrast two-tier, three-tier, and n-tier client-server architectures. What are the technical differences, and what advantages and disadvantages does each offer? Client-Server Architectures Two-Tier Three-Tier These networks use only two sets of computers, one set of clients and one set of servers. In the simplest case, the client is responsible for the presentation logic, whereas the server is responsible for the data access logic and data storage. The application logic may either reside on the client, on the server, or be split between both. Example: Utilization of a Web browser to get pages from a Web server. These networks use three sets of computers. In this case, the software on the client computer is responsible for presentation logic, an Application server (middle tier) is responsible for the application logic, and a separate Database server is responsible for the data access logic and data storage. Example: Utilizing the Hangman game. At the client side, a Java applet contained in a web page (originally obtained from a web server) is responsible for the application's graphical user interface. The N-Tier These networks use more than three sets of computers and are more typical across complex organizations. In a typical case, the client is responsible for presentation logic, a database server is responsible for the data access logic and data storage, and the application logic is spread across two or more different sets of servers such as Web or Application. Example: Utilization of which has 1,000 Web servers, e-mail servers, and database servers. The Web main site Technical Differences Page 1 IS589 Networking Concepts and Applications Homework week 1 October 26, 2010 server in the middle tier is a Java application and the business rules are coded in this tier. Sockets and JDBC, respectively, are used to communicate with the client and the data server through TCP/IP. forward Web requests to the different servers depending on how busy they are. The site handles simple requests for Web pages, search requests, job postings and resumes on file, spread across its database servers. Several copies of each posting and resume are kept on several database servers to improve access speed and provide redundancy in case a server crashes. Better load balancing: More evenly distributed processing. (e.g., application logic distributed between several servers.) More scalable: Only servers experiencing high demand need be upgraded. More efficient because of distributed processing. Allow hardware and software from different vendors to be used together. Advantages The added modularity makes it easier to modify or replace one tier without affecting the other tiers. Separating the application functions from the database functions makes it easier to implement load balancing. Scalability: The key 3-tier benefit is improved scalability since the application servers can be deployed on many machines. Also, the database no longer requires a connection from every client -- it only requires connections from a smaller number of application servers. Adequate security . Page 2 IS589 Networking Concepts and Applications Homework week 1 October 26, 2010 policies can be enforced within the server tiers without hindering the clients. Difficulty in getting software from different vendors to work together smoothly. May require Middleware, a third category of software that sits between the application software on the client and the application software on the server. Middleware provides a standard way of communicating that can translate between software from different vendors , manages the message transfer from clients to servers (and vice versa) so that clients need not know the specific server that contains the applications data and insulates network changes from the clients. an increased need for network traffic management, server load balancing, and fault tolerance. Current tools are relatively immature and are more complex. Maintenance tools are currently inadequate for maintaining server libraries. This is a potential obstacle for simplifying maintenance and promoting code reuse throughout the organization. Heavily loaded network: More distributed processing necessitates more data exchanges Difficult to program and test due to increased complexity Disadvantages Page 3 ... View Full Document

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