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Computer Network

by Rakesh Chaudhary
Type: NoteInstitute: trivuwan university Downloads: 23Views: 601Uploaded: 30 days agoAdd to Favourite

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Rakesh Chaudhary
Rakesh Chaudhary
Computer Networks A NOTE On Computer Networks (For B.Sc. CSIT FIFTH Semester, TU) By Loknath Regmi Er. Loknath Regmi Page 1
Computer Networks 1.1 Computer Network Unit I Network is the collection of computer, software and hardware that are all connected to each other to help their work together. A network connects computers by means of cabling system (or wireless media), specialized software and devices that manage data traffic. A network enables users to share files and resources such as printer as well as send message electrically to each other. Computer network falls under two types 1) Client-Server network 2) P2P (peer-to-peer) network  Client-Server Network Each client is assigned as account name and password that is verified by an authentication service. The authentication service guards access to the network. With the centralization of user accounts, security and access control, server based networks simplify the administration of large network. The concentration of network resources such as files, printers and applications on servers also makes it easier to backup and maintain the data. Resource can be located on specialized dedicated servers for easier access. Advantages - Easier to administer when the network is large. - All data can be backed up on one central location. Disadvantages - Requires expensive, more powerful hardware for the server machines. - Has a single point of failure. User data is unavailable when the server is down. - Requires expensive specialized network administrative and operational software. - Requires a professional administrator.  Peer-to-Peer Network Network computers act as equal partners, or peers. Each computer can take on the client function or the server function. Suppose computer A may request for a file from computer B, which then sends file to computer A. In this case, computer A acts like the client and computer B as server. At a later time, their role may be reserved; individual users control their own resources. The users may decide to share certain files with other users. The users may also require passwords before they allow others to access their resources. Since individual users make these decisions, there is no central point of control or administration in the network. When a computer acts as a server, the user of that machine may experience reduced performance as the machine serves the requests made by other system. Advantages - Less expensive to implement. - Doesn’t require additional specialized network administration software. - Doesn’t require a dedicated network administrator. Disadvantages Er. Loknath Regmi Page 2
Computer Networks - Less secure. Doesn’t scale well to large networks, and administration becomes unmanageable. Each must be trained to perform administrative tasks. All machines sharing resources negatively impact the performance. Advantages and Disadvantages of Computer Network   Advantages 1. File Sharing The major advantage of a computer network is that it allows file sharing and remote file access. A person sitting at one work station that is connected to a network can easily see files present on another workstation provided he/she is authorized to do so. If the files are stored on server and all of its clients share that storage capacity, then it becomes easier to make a file available to multiple users. 2. Resource Sharing For example, if there are twelve examples in an organization, each having their own computers, they will require twelve modems and twelve printers if they go to use resources at the same time. A computer network on the other hand provides cheaper alternative by the provision of resources sharing. All computers can be interconnected using a network and just one modem and printer can efficiently provides the services to all twelve users. 3. Inexpensive Set-Up Shared resources mean reduction in hardware costs. Shared files means reduction in memory requirements, which indirectly means reduction in file storage expenses. 4. Flexible Handling A user can log on to the computer anywhere on the network and access his/her files. This offers flexibility to the user as to where he/she should be during the course of his/her routine. 5. Increased Storage Capacity A standalone computer might fall short of storage memory, but when many computers are on a network the memory of different computers can be used in such a case. Disadvantages 1. Security If a computer is on a network, a hacker can get unauthorized access by using different tools. In case of big organizations, various security software need to be used to prevent theft of any confidential and classified data. 2. Virus Attack If even one computer on a network gets affected by a virus, there is a possible threat for the other systems getting affected too. Viruses can spread on a network easily because of interconnectivity of workstations. 3. Lack Of Robustness If the main file server of computer network breaks down, the entire system becomes useless. 4. Need Of Expert Handler The technical skills and know-how required to operate and administer a computer network is considerably high. 5. Lack Of Independence Since most computers have a centralized server and dependent clients, the clients/users lack any freedom whatsoever. Er. Loknath Regmi Page 3
Computer Networks Network Edge  End System  End system are also referred to as host because they host (i.e. run) application program such as a web browser program, a web server program, an email reader program.  Host are further divided into two categories:  Clients  Servers  Informally, clients tend to be desktop and mobile pc’s and so on, whereas servers tend to be more powerful machine that stores and distribute web pages, stream video so on.  Clients and Servers  A client is a program running on one end system that requests and receive a service from a server running on other end system.  Not all internet applications are client-server model, they are also peer-to-peer model like Bit Torrent and eMute. Network Core  It means the approach to moving data through a network of links and switches.  There are two types:  Circuit Switching  Packet Switching  In circuit switched network, the resources needed along a path (buffer, link transmission rate) to provide for communication between the end systems are reserved for the duration of the communication session between the end systems.  It reserves a constant transmission rate in the network’s links for the duration of the communication. Since bandwidth has been reserved for this sender-to-receiver. Connection, the sender can transfer the data to the receiver at the guaranteed constant rate.  In packed switched network, the resources are not reserved; a session’s message use the resources on demand, and as a consequence, may have to wait (i.e. queue) for access to a communication link.  The packet is sent into the network without reserving bandwidth and if one of the links is busy because other packets need to be transmitted over the link at the same time, our packet will have to wait in a buffer at the sending side of the transmission link, and suffer a delay. There are two approaches in packet switched network 1. Datagram Network  Any network that forwards the packets according to the destination address is called a datagram network.  The routers in the internet forwards packets according to the destination address. Hence, internet is datagram network. 2. Virtual Circuit Network  Any network that forwards the packets according to virtual circuit identifier (fixed route) is called a virtual circuit network.  Preplanned route established before packets sent.  Examples are X.25, Frame relay, ATM technologies. Er. Loknath Regmi Page 4

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