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Note for Computer Network - CN By SARMI SASIREKHA

  • Computer Network - CN
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UNIT –III LOCAL AREA NETWORK & UPPER LAYERS Syllabus  Aloha,  Slotted aloha  IEEE 802 Standards  IEEE 802.1,  LLC,  MAC,  PDU,  ETHERNET: Access method, addressing, Frame Format, Implementation,  Switched Ethernet,  Fast Ethernet,  Gigabit Ethernet,  Token Bus,  Token Ring,  FDDI,  OSI layers: Network Layer,  Transport Layer,  Session Layer,  Presentation Layer,  Application Layer,  Networking and Internetworking devices :Overview of repeaters,  Bridges,  Routers,  Gateways,  Hubs.  TCP: TCP Services, TCP Header Format,  FTP,  SMTP,  HTTP. INTRODUCTION The networks can be divided into two categories as follows:   Point-to-point network Broadcast network In any broadcast network, the key issue is how to determine who gets to use the channel when there is competition for it. Broadcast channels are sometimes referred to as multi access channels or random access channels. The protocols used to determine who goes next on a multi access channel belong to a sublayer of the data link layer called the MAC (Medium Access Control) sublayer.

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COMPUTER NETWORK UNIT II Syllabus  Introduction  Perspective of network  Protocols and standard  Network Topologies  Transmission Mode  Categories of network-LAN, MAN, WAN,  OSI Model  Functions of the layer  TCP/IP Protocol suit  Line Configuration  Asynchronous and Synchronous mode. Physical layer • Digital data transmission • DTE-DCE Interface • Other Interface Standard • V.24 Null Modem • Modem Standards • Cable Modem • Transmission Media Data Link layer • • • • • 1. Types of Errors Error Detection and Correction Methods Flow Control HDLC Brief Details of Data Link Protocols. INTRODUCTION Networks exist so that data may be sent from one place to another. Data communications between remote parties can be achieved through a process called networking, involving the connection of computers, media, and networking devices. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. For data communications to occur, the communicating devices must be part of a communication system made up of a combination of hardware (physical equipment) and software (programs).

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Data Communication may be of two types Local Remote If the communicating devices are in the same building then it is a type of local communication If the devices are farther apart then it is a type of remote communication The effectiveness of a data communications system depends on these fundamental characteristics: Delivery: The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user. Accuracy: The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable. Timeliness: The system must deliver data in a timely manner. Data delivered late are useless. In the case of video and audio, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is called real-time transmission. Components of data communication Figure 2.1 Components of data communication A data communications system has five components Message: The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video. Sender: The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on. Receiver: The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on. Transmission medium: The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves. Protocol: A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese.

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Goals of Networking      2. The main goal of networking is "Resource sharing", and it is to make all programs, data and equipment available to anyone on the network without the regard to the physical location of the resource and the user. A second goal is to provide high reliability by having alternative sources of supply. For example, all files could be replicated on two or three machines, so if one of them is unavailable, the other copies could be available. Another goal is saving money. Small computers have a much better price/performance ratio than larger ones. Mainframes are roughly a factor of ten times faster than the fastest single chip microprocessors, but they cost thousand times more. This imbalance has caused many system designers to build systems consisting of powerful personal computers, one per user, with data kept on one or more shared file server machines. This goal leads to networks with many computers located in the same building. Such a network is called a LAN (local area network). Another closely related goal is to increase the systems performance as the work load increases by just adding more processors. With central mainframes, when the system is full, it must be replaced by a larger one, usually at great expense and with even greater disruption to the users. Computer networks provide a powerful communication medium. A file that was updated/modified on a network can be seen by the other users on the network immediately. PERSPECTIVE OF NETWORK A network is a collection of autonomous computer. The computers which can forcibly start, stop and control another one are not autonomous. Two computers are said to be interconnected if they are able to exchange information. Network criteria Figure 2.2 Network Criteria Performance: It can be measured in many ways including the response Time. It depends on the following factors, they are  Number of users: Having a large number of concurrent users can slow response time in a network not designed to co-ordinate heavy loads. The design of a given network is

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