Computer networks
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Computer networks allow for resource sharing, high reliability, and powerful communication between connected devices. ARPANET, developed in the 1960s-70s, was an early network and precursor to the modern Internet. It connected computers at universities and defense organizations in the US. Computer networks have various applications including information sharing for businesses, e-commerce, remote access to information for homes, and communication between mobile users. Network hardware includes network interface cards, servers, routers, switches, and different types of cables. Network software includes operating systems, protocols like TCP/IP and OSI, and applications that allow devices to connect and communicate over the network.
Computer networks
- 1. COMPUTER NETWORKS ….Basic Introduction of Computer Network ABSTRACT This is a notes about basic introduction of computer networks. It contain details about the definition of computer network, ARPANET, goals of computer network, application of computer network and details about networking hardware & software components. Supervised By Pranab Bandhu Nath (Senior Lecturer) CSE Department City University, Dhaka Submitted By Shamima Akther| ID - 1834902616 CSE 317 : Computer Networks
- 2. “Computer Networks” ARPANET: Arpanet was the network that became basis for the internet. It stands for Advanced Research Project Agency Network.Based on a concept first published in 1967, ARPANET was developed under the direction of the U.S Advanced Research Projects Agency (ARPA).It is a project sponsored by U.S Department of Defense and planted in 1969 to connect computers at U.S Defense and different universities. ARPAET is sometimes referred to as DARPANET , Because ARPA’s name was changed to Defense Advanced Research Projects Agency (DARPA) in 1971. In 1980s, NSFnet was started to make high capacity network, which are more capable than ARPANET. In 1990s the internetworking of ARPANET, NSFnet and other private networks resulted into internet. NETWORK: In information technology , a network is defined as the connection of atleast two computer systems, either by a cable or wireless connection. The simplest network is a combination of two computers connected by a cable. COMPUTER NETWORK: A computer network is a group of two or more computers or other electronic devices that are interconnected for the purpose of exchanging data and sharing resources. It can transmit, receive and exchange data, voice and video traffic. GOALS OF COMPUTER NETWORK: The following are some important goals of computeer networks:- • Resource Sharing: It is one of from main goals of networking to make all programs, data and equipment available to anyone on the network without regard to the physical location of the resource and the user. • High Reliability: If there are alternate sources of supply, all files could be replicated on two or more machines. Due to connectivity issue or hardware failures, if one of them is not available, the other copies could be used. • Performance: To increase the systems performances as the work load increases by just adding more processors. With central mainframes when the system is full, it must be reeplaced by a larger one, usually at great expense and with even greater disruption to the users. • Saving Money: Computer organization has helped organization in saving money. This is due to the fact that the small computer has much better price to the performance ratio comparison than the large computer like mainframe. Mainframe computer are approximately ten times faster that the microcomputers, but they cost thousands times more. As a result of this imbalance, organization has preferred to install interconnected microcomputer connected to the mainframe computer.
- 3. • Powerful Communication Medium: Computer Network help people who live or work apart to report together. So a file that was updated or modified on a network from any user, can be seen by the other users on the network immediately. • Security: Only authorized user can access resource in a computer network. Users are authenticated by their user name and password. Hence it means protecting data from unathorized access. This increases security. • Flexible Access: Files can be accessed from any computer in the network. The project can be begun on one computer and finished on another. • Scalability: To increase the systems performance as the work load increases by just adding more processors. • Inter-Process Communication: Network users, located geographically apart, may converse in an interactive session through the network. In order to permit this, the network must provide almost error-free communications. APPLICATION OF COMPUTER NETWORK: ❖ Business Applications: Among business applications the highlighted points are given below:- • Information & Resource Sharing: Computer networks allow organizations having units which are placed apart from each other, to share information in a very effective manner. Programs and software in any computer can be accessed by other computers linked to the network. It also allows sharing of hardware equipment, like printers and scanners among varied users. • Server-Client model: The individual workstations in the network are called as clients. The central computer which is more powerful than the clients and which allows the clients to access it's software and database is called as the server. In this model the client places a request on the server machine when he wants an access to the centralized resources & the server responds to this request and sends the signal accordingly to the client. Here, Organization can use separate personal computer one per user instead of using mainframe computer which are expensive. The organizations can use the work-group model (peer to peer) in which all the PC's are networked together and each one can have the access to the other for communicating or sharing purpose. The organization, if it wants security for its operation it can go in for the domain model in which there is a server and clients. All the clients can communicate and access data through the server. The whole arrangement is called as client-server model. • Communication Medium: Computer networks have increased the speed and the volume of communication like never before. A computer network provides a powerful communication medium among widely separated employees. Using network it is easy for two or more employees, who are separated by geographical locations to work on a report, document or R and D simultaneously i.e on-line.
- 4. • E-Commerce: Computer networks have paved way for a variety of business and commercial transactions online, popularly called e-commerce. Users and organizations can pool funds, buy or sell items, pay bills, manage bank accounts, pay taxes, transfer funds and handle investments electronically. ❖ Home Applications: Some of the most important uses of the internet for home users are as follows:- • Access to remote information: Access to remote information involves interaction between a person and a remote database. It comes in many forms like: ➢ Home shopping, paying telephone, electricity bills, e-banking, on line share market etc. ➢ Newspaper is On-line and is personalized, digital library consisting of books, magazines, scientific journals etc. ➢ World wide web which contains information about the arts, business, cooking, government, health, history, hobbies, recreation, science, sports etc. • Person to person communication: It helps to communicate & share information through mails,phone calls, messages at very fast speed. It includes:- ➢ Electronic-mail (e-mail). ➢ Real time e-mail i.e. video conferencing allows remote users to communicate with no delay by seeing and hearing each other. Video- conferencing is being used for remote school, getting medical opinion from distant specialists etc. ➢ Worldwide newsgroups in which one person posts a message and all other subscribers to the newsgroup can read it or give their feedback’s. • Interactive entertainment: It includes:- ➢ Multi-person real-time simulation games. ➢ Video on demand. ➢ Participation in live TV programmes like quiz, contest, discussions etc. In short, the ability to merge information, communication and entertainment will surely give rise to a massive new industry based on computer networking. ❖ Mobile Users: Mobile computers such as notebook computers and Mobile phones is one of the fastest-growing segment of the entire computer industry. Although wireless networking and mobile computing are often related, they are not identical. NETWORK HARDWARE & SOFTWARE: There are three component of computer network. They are briefly described below:- ❖ HARDWARE EQUIPMENT: The hardware equipment for networks are-:- • NIC : Network card is a necessary component of a computer without which a computer cannot be connected over a network. It is also known as the network
- 5. adapter or Network Interface Card (NIC). Most branded computers have network card pre-installed. Network cards are of two types: Internal and External Network Cards. • Servers & Clients: Servers are computers that hold shared programs, files and the network operating system. Servers allow access to network resources to all the users of the network. On the other hand, Clients are computer devices which access and uses the network as well as shares network resources. They are also users of the network as they can send and receive requests from the server. • Peers: Stands for "Peer to Peer". In a peer to peer network, the "peers" are computer systems which are connected to each other via the Internet. Files can be shared directly between system's on the network without the need of a central server. In other words, each computer on a P2P network becomes a file server as well as a client. In any of the peer-to-peer networks, all the nodes generally have equal power and can use the same tasks.
- 6. • Transmission Media: Transmission media is a carrier used to interconnect computers in a network, such as coaxial cable, twisted-pair wire, and optical fiber cable. It is also known as links, channels or lines. The type of transmission media can be illustrated more thoroughly with this graphical representation which is given below:- • Router: A router is a type of device which acts as the central point among computers and other devices that are a part of the network. It is equipped with holes called ports. This networking component acts as a dispatcher, which allows us to analyze data sent across a network. It automatically selects the best route for data to travel and send it on its way. Computers and other devices are connected to a router using network cables. Now-a-days router comes in wireless modes using which computers can be connected without any physical cable.
- 7. • Bridge: A bridge operates at data link layer. A bridge is a repeater, with add on the functionality of filtering content by reading the MAC addresses of source and destination. It is also used for interconnecting two LANs working on the same protocol. It has a single input and single output port, thus making it a 2 port device. • Hub: Hub is a device that splits network connection into multiple computers. It acts a distribution center so whenever a computer requests any information from a computer or from the network it sends the request to the hub through a cable. The hub will receive the request and transmit it to the entire network.
- 8. • Switches: Switches work as a controller which connects computers, printers and other hardware devices to a network in a campus or a building. It allows devices on your network to communicate with each other, as well as with other networks. It helps you to share resources and reduce the costing of any organization. • Gateway: A gateway is a hardware device that acts as a "gate" between two networks. It may be a router, firewall, server or other device that enables traffic to flow in and out of the network. It allows computers within the local network to send and receive data over the internet.
- 9. • Repeater: In telecommunications, a repeater is an electronic device that receives a signal and retransmits it. So, it is a network device used to regenerate or replicate a signal. Repeaters are used in transmission systems to regenerate analog or digital signals distorted by transmission loss. Analog repeaters frequently can only amplify the signal while digital repeaters can reconstruct a signal to near it's original quality.
- 10. ❖ SOFTWARE: The software systems for networks are-:- • Network Operating System: Network Operating System is a computer operating system that facilitates to connect and communicate various autonomous computers over a network. The basic purpose of the network operating system is to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks. • Protocols Switches (TCP/IP, OSI): A protocol is a set of rules for communication between computers within a layer on a network. Layers provide a division of the work done by a network. These rules include guidelines that regulate the following characteristics of a network: access method, allowed physical topologies, types of cabling and speed of data transfer. As we know, In computer science, Computers communicate using a layered set of protocols. There are two models that are widely referenced today : OSI and TCP/IP. The concepts are similar, but the layers themselves differ between the two models. OSI: OSI referred to the open Systems Interconnection (OSI). This is a model that was proposed as a set of standard layers and protocols for communication between different computers around the world and has been in use since 1983. Although not universally adopted, much of this model is considered the standard and in heavy use layers provide a division of the work done by a network. In OSI model, It has seven layer in total. They are given below:- ➢ Layer 7 (Application): Most of what the user actually interacts with is at this layer. Web browsers and other internet-connected applications (like Skype or Outlook) use Layer 7 application protocols. ➢ Layer 6 (Presentation): This layer converts data to and from the Application layer. In other words, it translates application formatting to network formatting and vice versa. This allows different layers to understand each other. ➢ Layer 5 (Session): This layer establishes and terminates connections between devices. It also determines which packets belong to which text and image files. ➢ Layer 4 (Transport): This layer coordinates data transfer between system and hosts, including error-checking and data recovery. ➢ Layer 3 (Network): This layer determines how data is sent to the receiving device. It's responsible for packet forwarding, routing and addressing. ➢ Layer 2 (Data Link): Translates binary (or BITs) into signals and allows upper layers to access media. ➢ Layer 1 (Physical): Actual hardware sits at this layer. It transmits signals over media.
- 11. TCP: The TCP (Transmission Control Protocol)/IP (Internet Protocol) model, sometimes referred to as a protocol stack, can be considered a condensed version of the OSI model. As we know, This model does not cover the two layers of the OSI model. This means that TCP/IP is hardware independent. Since TCP/IP does not include lower level protocols, we'll start with the middle level protocols. TCP/IP has four layers. Such as:- ➢ Layer 1 (Network Access): Also called the Link or Network Interface layer. This layer combines the OSI model’s L1 and L2.. ➢ Layer 2 (Network): This layer is similar to the OSI model’s L3. ➢ Layer 3 (Transport): Also called the Host-to-Host layer. This layer is similar to the OSI model’s L4. ➢ Layer 4 (Application): Also called the Process Layer, this layer combines the OSI model’s L5, L6 and L7. ❖ CABLES & CONNECTORS: There are three Types of Cables. They are:- • Twisted Pair Cable: A twisted-pair caible is a cable made by interwinning two separate insulated wires. There are two twisted pair types: shielded and unsheilded. A STP(Sheilded Twisted Pair) Cable has a fine wire mesh surrounding the wires to protect the transmission and a UTP(Unsheilded Twisted Pair) cable does not. Shielded Cable is used in older telephone networks and network and data communications to reduce outside interference. The illustration gives an example of how it looks: • Coaxial cable: Coaxial cable is a type of cable that has an inner conductor surrounded by an insulating layer, surrounded by a conductive sheilding. Many also have an insulating outer jacket. The term “coaxial” refers to the inner conductor and the outer sheild sharing a geometric axis.
- 12. • Fiber-optic cable: A fiber optic cable is a network cable that contains strands of glass fibers inside an insulated coating. They’re designed for long-distance, high- performance data networking, and telecommunicatons. Compared to wired cables, fiber optic cables provide higher bandwidth and transmit data over longer distances. Fiber optic cables support much of the world’s interne, cable television, and telephone systems.