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Note for Computer Network - CN By ANNA SUPERKINGS

  • Computer Network - CN
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  • Computer Science Engineering
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Course Material –Lecture Notes UNIT I FUNDAMENTALS & LINK LAYER Building a network: A computer network or data network is a telecommunications network which allows computers to exchange data. In computer networks, networked computing devices pass data to each other along network links (data connections). Data is transferred in the form of packets. The connections between nodes are established using either cable media or wireless media. The bestknown computer network is the Internet. To build a computer network is defining what a network is and understanding how it is used to help a business meet its objectives. A network is a connected collection of devices and end systems, such as computers and servers, which can communicate with each other. These are the four major categories of physical components in a computer network: Personal computers (PCs): The PCs serve as endpoints in the network, sending and receiving data. Interconnections: The interconnections consist of components that provide a means for data to travel from one point to another point in the network. This category includes components such as the following: o Network interface cards (NICs) that translate the data produced by the computer into a format that can be transmitted over the local network o Network media, such as cables or wireless media, that provide the means by which the signals are transmitted from one networked device to another o Connectors that provide the connection points for the media Switches: Switches are devices that provide network attachment to the end systems and intelligent switching of the data within the local network. Routers: Routers interconnect networks and choose the best paths between networks. Network User Applications: The key to utilizing multiple resources on a data network is having applications that are aware of these communication mechanisms. Although many applications are available for users in a network environment, some applications are common to nearly all users. The most common network user applications include the following: E-mail: E-mail is a valuable application for most network users. Users can communicate information (messages and files) electronically in a timely manner, to not only other users in the same network but also other users outside the network (suppliers, information resources, and customers, for example). Examples of e-mail programs include Microsoft Outlook and Eudora by Qualcomm. CS 6551 Computer Networks – Unit-I Page 1

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Course Material –Lecture Notes Web browser: A web browser enables access to the Internet through a common interface. The Internet provides a wealth of information and has become vital to the productivity of both home and business users. Communicating with suppliers and customers, handling orders and fulfillment, and locating information are now routinely done electronically over the Internet, which saves time and increases overall productivity. The most commonly used browsers are Microsoft Internet Explorer, Netscape Navigator, Mozilla, and Firefox. Instant messaging: Instant messaging started in the personal user-to-user space; however, it soon provided considerable benefit in the corporate world. Now many instant messaging applications, such as those provided by AOL and Yahoo!, provide data encryption and logging, features essential for corporate use. Collaboration: Working together as individuals or groups is greatly facilitated when the collaborators are on a network. Individuals creating separate parts of an annual report or a business plan, for example, can either transmit their data files to a central resource for compilation or use a workgroup software application to create and modify the entire document, without any exchange of paper. One of the best-known traditional collaboration software programs is Lotus Notes. A more modern web-based collaboration application is a wiki. Database: This type of application enables users on a network to store information in central locations (such as storage devices) so that others on the network can easily retrieve selected information in the formats that are most useful to them. Some of the most common databases used in enterprises today are Oracle and Microsoft SQL Server Requirements: An application programmer would list the services that his or her application needs—for example, a guarantee that each message the application sends will be delivered without error within a certain amount of time or the ability to switch gracefully among different connections to the network as the user moves around. A network operator would list the characteristics of a system that is easy to administer and manage—for example, in which faults can be easily isolated, new devices can be added to the network and configured correctly, and it is easy to account for usage. A network designer would list the properties of a cost-effective design—for example, that network resources are efficiently utilized and fairly allocated to different users. Issues of performance are also likely to be important. This section attempts to distill these different perspectives into a high-level. CS 6551 Computer Networks – Unit-I Page 2

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Course Material –Lecture Notes Layering and protocols: OSI Architecture: ISO defines a common way to connect computer by the architecture called Open System Interconnection(OSI) architecture. Network functionality is divided into seven layers. Organization of the layers The 7 layers can be grouped into 3 subgroups 1. Network Support Layers Layers 1,2,3 - Physical, Data link and Network are the network support layers. They deal with the physical aspects of moving data from one device to another such as electrical specifications, physical addressing, transport timing and reliability. 2. Transport Layer Layer4, transport layer, ensures end-to-end reliable data transmission on a single link. 3. User Support Layers Layers 5,6,7 – Session, presentation and application are the user support layers. They allow interoperability among unrelated software systems CS 6551 Computer Networks – Unit-I Page 3

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Srividya College of Engineering and Technology, Virudhunagar. Course Material –Lecture Notes An Data exchange using the OSI model Functions of the Layers 1. Physical Layer The physical layer coordinates the functions required to transmit a bit stream over a physical medium. The physical layer is concerned with the following: Physical characteristics of interfaces and media - The physical layer defines the characteristics of the interface between the devices and the transmission medium. Representation of bits - To transmit the stream of bits, it must be encoded to signals. The physical layer defines the type of encoding. Data Rate or Transmission rate - The number of bits sent each second – is also defined by the physical layer. Synchronization of bits - The sender and receiver must be synchronized at the bit level. Their clocks must be synchronized. CS 6551 Computer Networks – Unit-I Page 4

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