Computer-based systems

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Any system which uses a microprocessor or computer for controlling or executing the task it is designed to perform can be called a computer based system. In complex systems computers play a major role. While complex physical systems and sophisticated software systems can help people to lead healthier and more enjoyable lives, reliance on these systems can also result in loss of money, time, and life when these systems fail. Much of the complexity of these systems is due to integration of information technology into physical and human activities. Such integration dramatically increases the interdependencies among components, people, and processes, and generates complex dynamics not taken into account in systems of previous generations. Engineers with detailed understanding both of the application domain and computer electronics, software, human factors, and communication are needed to provide a holistic approach to system development so that disasters do not occur. Engineering activities The computer-based systems engineer develops a system within a system; the properties of the former have pervasive effects throughout the larger system. The computer-based system consists of all components necessary to capture, process, transfer, store, display, and manage information. Components include software, processors, networks, buses, firmware, application-specific integrated circuits, storage devices, and humans (who also process information). Embedded computer-based systems interact with the physical environment through sensors and actuators, and also interact with external computer-based systems (see illustration). The computer-based systems engineer must have a thorough understanding of the system in which the computer-based system is embedded, for example an automobile, medical diagnostic system, or stock exchange. Model-based development Models are necessary in systems engineering as they support interdisciplinary communication, formalize system definition, improve analysis of trade-offs and decision making, and support optimization and integration. The use of models can reduce the number of errors in the design and thus the system, reduce engineering effort, and preserve knowledge for future efforts. Maintaining models with up-to-date knowledge is a major problem as most systems are not generated from models, although this should be an industry goal. During the later stages of system development and testing, significant schedule pressure makes it difficult to keep the models and manually developed software consistent A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information. Where at least one process in one device is able to send/receive data to/from at least one process residing in a remote device, then the two devices are said to be in a network.

which defines a set of protocols for internetworking. George Stibitz used a Teletype machine to send instructions for a problem set from his Model at Dartmouth College to his Complex Number Calculator in New York and received results back by the same means. J. started in the late 1950s. computer science. 1965 Thomas Merrill and Lawrence G.[2][3] In 1964. Linking output systems like teletypewriters to computers were an interest at the Advanced Research Projects Agency (ARPA) when. telecommunications.C. and the Internet Protocol Suite. communication between calculation machines and early computers was performed by human users by carrying instructions between them. information technology or computer engineering. Communications protocols define the rules and data formats for exchanging information in a computer network. . scale. and organizational scope. in 1962. Throughout the 1960s Leonard Kleinrock. as well as host-to-host data transfer. Roberts created the first wide area network (WAN). i. Well-known communications protocols are Ethernet. The commercial airline reservation system semi-automatic business research environment (SABRE) went online with two connected mainframes in 1960. The first widely used telephone switch that used true computer control was introduced by Western Electric in 1965. a research group supported by General Electric and Bell Labs used a computer to route and manage telephone connections.R. at Massachusetts Institute of Technology. topology. and application-specific data transmission formats. communications protocol used. • • • • • • • In September 1940. researchers at Dartmouth developed the Dartmouth Time Sharing System for distributed users of large computer systems. for data communication between multiple networks. Computer networking is sometimes considered a sub-discipline of electrical engineering. Paul Baran and Donald Davies independently conceptualized and developed network systems which used packets that could be used in a network between computer systems. a hardware and Link Layer standard that is ubiquitous in local area networks. Licklider was hired and developed a working group he called the "Intergalactic Network".Networks may be classified according to a wide variety of characteristics such as the medium used to transport the data.e. The same year. Early networks of communicating computers included the military radar system Semi-Automatic Ground Environment (SAGE). since it relies upon the theoretical and practical application of these disciplines. Many of the social behaviors seen in today's Internet were demonstrably present in the 19th century and arguably in even earlier networks using visual signals. and provide the basis for network programming. History: Before the advent of computer networks that were based upon some type of telecommunications system. a precursor to the ARPANET.

Following are the types of network. although new standards like ITU-T G. Network Types: . because they are handling multiple subnets (the different colors).hn also provide a way to create a wired LAN using existing home wires (coaxial cables. University of California at Santa Barbara. Computer networks. which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central router. A wired PAN is usually constructed with USB and Fire wire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN. Commercial services using X. and the technologies needed to connect and communicate through and between them. . computer laboratory. and the University of Utah were connected as the beginning of the ARPANET network using 50 kbit/s circuits. This expansion is mirrored by growth in the numbers and types of users of networks. fax machines. continue to drive computer hardware. although not necessarily the public Internet. Today. Those inside the library. Personal area network A personal area network (PAN) is a computer network used for communication among computer and different information technological devices close to one person.25 were deployed in 1972. and peripherals industries. Each computer or device on the network is a node. The reach of a PAN typically extends to 10 meters. scanners. printers. All interconnected devices must understand the network layer (layer 3). software. or closely positioned group of buildings. school. phone lines and power lines). PDAs. the Stanford Research Institute. It would be more correct to call them access routers. and this boom in communications would not have been possible without the progressively advancing computer network. telephones. and even video game consoles. where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers. and later used as an underlying infrastructure for expanding TCP/IP networks. computer networks are the core of modern communication. Some examples of devices that are used in a PAN are personal computers. Local area network A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as home. The scope of communication has increased significantly in the past decade. A PAN may include wired and wireless devices. All modern aspects of the public switched telephone network (PSTN) are computer-controlled. from the researcher to the home user.• • In 1969 the University of California at Los Angeles. could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP. Current wired LANs are most likely to be based on Ethernet technology. office building. and telephony increasingly runs over the Internet Protocol.

providing a path for the exchange of information between different LANs or sub networks. for example.) are almost entirely owned (by the campus tenant / owner: an enterprise. and no need for leased telecommunication lines. A large corporation which has many locations may have a backbone network that ties all of these locations together. copper plant. or over wide areas. such as printers and mobile computing devices. IEEE has projects investigating the standardization of 40 and 100 Gbit/s. and optical jukeboxes. In the case of a university campus-based campus network. the university library. smaller geographic range. An important function is the sharing of Internet access.). for example. LANs can be connected to Wide area network by using routers. in contrast to WANs (Wide Area Networks). if a server cluster needs to be accessed by different . Backbone network A backbone network is part of a computer network infrastructure that interconnects various pieces of network. Current Ethernet or other IEEE 802. the backbone's capacity is greater than that of the networks connected to it. SANs are primarily used to make storage devices. A SAN typically has its own network of storage devices that are generally not accessible through the local area network by other devices. block level data storage. Home area network A home area network (HAN) is a residential LAN which is used for communication between digital devices typically deployed in the home. government etc. The networking equipment (switches.3 LAN technologies operate at speeds up to 10 Gbit/s. such as disk arrays. university.The defining characteristics of LANs. Cat5 cabling etc. and student residence halls. Storage area network A storage area network (SAN) is a dedicated network that provides access to consolidated. tape libraries. in different buildings in a campus environment. the network is likely to link a variety of campus buildings including. academic colleges or departments. often a broadband service through a cable TV or Digital Subscriber Line (DSL) provider. Campus area network A campus area network (CAN) is a computer network made up of an interconnection of LANs within a limited geographical area. This is the data transfer rate. routers) and transmission media (optical fiber. The cost and complexity of SANs dropped in the early 2000s to levels allowing wider adoption across both enterprise and small to medium sized business environments. Normally. include their higher data transfer rates. accessible to servers so that the devices appear like locally attached devices to the operating system. usually a small number of personal computers and accessories. A backbone can tie together diverse networks in the same building.

The equipment which ties these departments together constitutes the network backbone. or spans even intercontinental distances. using a communications . country. which is the set of widearea network connections and core routers that interconnect all networks connected to the Internet. Wide area network A wide area network (WAN) is a computer network that covers a large geographic area such as a city. Sample EPN made of Frame relay WAN connections and dialup remote access. Metropolitan area network A Metropolitan area network (MAN) is a large computer network that usually spans a city or a large campus. Network performance management including network congestion is critical parameters taken into account when designing a network backbone. A specific case of a backbone network is the Internet backbone.departments of a company which are located at different geographical locations.

can be used to separate the traffic of different user communities over an underlying network with strong security features. networks are seen as intranets or extranets. or may have a defined service level agreement (SLA) between the VPN customer and the VPN service provider. and the network layer. An extranet is a network that is limited in scope to a single organization or entity and also has limited connections to the networks of one or more other usually. VPN may have best-effort performance. a VPN has a topology more complex than point-to-point. head offices. which has no single owner but a distinct status when seen by an organizational entity that of permitting virtually unlimited global connectivity for a great multitude of purposes. Generally.channel that combines many types of media such as telephone lines. production sites. the Internet) instead of by physical wires. but a VPN need not have explicit security features. cables.. Virtual private network A virtual private network (VPN) is a computer network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e. the data link layer. Enterprise private network An enterprise private network is a network built by an enterprise to interconnect various company sites. such as authentication or content encryption. That administrative entity closes the intranet to all but specific. but not necessarily. an intranet is the internal network of an organization. usually a LAN. Organizational scope Networks are typically managed by organizations which own them. for example. A special case of network is the Internet. and air waves.g. One common application is secure communications through the public Internet.g.. According to the owner's point of view. Intranets and extranets Intranets and extranets are parts or extensions of a computer network. Most commonly. authorized users. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer. such as telephone companies. A WAN often uses transmission facilities provided by common carriers. A large intranet will typically have at least one web server to provide users with organizational information. shops. . The data link layer protocols of the virtual network are said to be tunneled through the larger network when this is the case. VPNs. An intranet is a set of networks. e. in order to share computer resources. remote offices. using the Internet Protocol and IP-based tools such as web browsers and file transfer applications that are under the control of a single administrative entity.

A star network: all nodes are connected to a special central node. A mesh network: each node is connected to an arbitrary number of neighbors in such a way that there is at least one traversal from any node to any other. Service providers and large enterprises exchange information about the reach ability of their address spaces through the Border Gateway Protocol (BGP). called 10BASE5 and 10BASE2. WAN. A ring network: each node is connected to its left and right neighbor node. corporate. . It is the successor of the Advanced Research Projects Agency Network (ARPANET) developed by DARPA of the United States Department of Defense. Network topology Common layouts A network topology is the layout of the interconnections of the nodes of a computer network. A fully connected network: each node is connected to every other node in the network. Common layouts are: • • • • • A bus network: all nodes are connected to a common medium along this medium. although an extranet cannot consist of a single LAN. academic. MAN. where each wireless client connects to the central Wireless access point. or other type of network. The Fiber Distributed Data Interface (FDDI) made use of such a topology. it must have at least one connection with an external network. The Internet is also the communications backbone underlying the World Wide Web (WWW). and private computer networks. and often standardized. forming a redundant worldwide mesh of transmission paths. an extranet may also be categorized as a CAN. Participants in the Internet use a diverse array of methods of several hundred documented. This was the layout used in the original Ethernet. Internet The Internet is a global system of interconnected governmental.or rightwards. It is based on the networking technologies of the Internet Protocol Suite. protocols compatible with the Internet Protocol Suite and an addressing system (IP addresses) administered by the Internet Assigned Numbers Authority and address registries. public.trusted organizations or entities a company's customers may be given access to some part of its intranet while at the same time the customers may not be considered trusted from a security standpoint. such that all nodes are connected and that each node can reach each other node by traversing nodes left. This is the typical layout found in a Wireless LAN. Technically.

each having their own computer. ATM: In an Asynchronous Transfer Mode (ATM) network. on the other hand. data throughput. but when many . echo and so on. In addition to that. by using a storage device. The facility of shared folders can also be availed by family members. Performance can also be modeled instead of measured. ensuring that the network will be optimally designed. The following list gives examples of Network Performance measures for a circuit-switched network and one type of packet-switched network. A computer network. the issue of storage capacity gets resolved to a great extent. technology. one example of this is using state transition diagrams to model queuing performance in a circuit-switched network. A person sitting at one workstation of a network can easily see the files present on the other workstation. network performance is synonymous with the grade of service.Network performance Network performance refers to the service quality of a telecommunications product as seen by the customer. provided he is authorized to do so. • • • File Sharing: The major advantage of a computer network is that is allows file sharing and remote file access. they will require four modems (for the Internet connection) and four printers. many people can access or update the information stored in a database. modulation technique and modem enhancements. ATM: • Circuit-switched networks: In circuit switched networks. all the four computers can be interconnected. viz. making it up-to-date and accurate. provides a cheaper alternative by the provision of resource sharing. performance can be measured by line rate. A standalone computer might fall short of storage memory. using a network. Resource Sharing: Resource sharing is also an important benefit of a computer network. if there are four people in a family. Increased Storage Capacity: As there is more than one computer on a network which can easily share files. Other types of performance measures can include noise. Advantages of Computer Networks Following are some of the advantages of computer networks. quality of service (QoS). The number of rejected calls is a measure of how well the network is performing under heavy traffic loads. • There are many different ways to measure the performance of a network. stability. if they want to use the resources at the same time. and just one modem and printer can efficiently provide the services to all four members. It saves the time which is wasted in copying a file from one system to another. In this way. For example. These diagrams allow the network planner to analyze how the network will perform in each state. It should not be seen merely as an attempt to get "more through" the network. connect time. as each network is different in nature and design.

a computer hacker can get unauthorized access by using different tools. Such spread can be dangerous if the computers have important database which can get corrupted by the virus. Viruses get spread on a network easily because of the interconnectivity of workstations. In case of big networks. etc. It’s true this can be done with email. If a computer is a standalone. The Importance of Computer Networks in Business Employees in a business come into the company already capable of interacting with each other to share information and create new projects. the File Server should be a powerful computer. there is a possible threat of other systems getting affected too. The basic need of for most computers to interact in a business is to share files. can add up to the bills of a person trying to install a computer network. One can also design a storage server on the network in order to have a huge storage capacity. if a computer is on a network. Each of those computers are used to perform the employee’s job. the system becomes useless. increasing the interaction capability of the entire business. Disadvantages of Computer Networks Following are some of the major disadvantages of computer networks. However. They are connected in a network of speech. • • • • Security Issues: One of the major drawbacks of computer networks is the security issues involved. which often makes it expensive. Expensive Set Up: The initial set up cost of a computer network can be high depending on the number of computers to be connected. Rapid Spread of Computer Viruses: If any computer system in a network gets affected by computer virus. In nearly every business those same employees are using computers. but there is always the issue of a file being saved on someone’s . in case they are not inbuilt. memory of different computers can be used in such case. switches. Dependency on the Main File Server: In case the main File Server of a computer network breaks down. various network security software are used to prevent the theft of any confidential and classified data. In this arrangement each computer can connect to the other. so wouldn’t it make sense that they too communicate like their users? Many businesses are starting to agree. Increased Cost Efficiency: There are many software available in the market which are costly and take time for installation. Costly devices like routers. Computer networks resolve this issue as the software can be stored or installed on a system or a server and can be used by the different workstations..• computers are on a network. In case of big organizations. physical access becomes necessary for any kind of data theft. hubs. by networking all company computers in local area networks or LANs. He will also have to buy NICs (Network Interface Cards) for each of the workstations.

Instead of purchasing multiple printers for various groups. With a network. Additionally. Employing a network can in some cases save money for a business in equipment costs as well. and with a networking system each employee can stay organized by staying on the same page. as well as brainstorm.computer who is absent. It is an ideal system for businesses with employees that need to travel and still access information when needed. computer networks can be outfitted with remote access so employees can grab and share files from outside of the office like on their home computers or smart phones. much more efficiently in an open setting in which additional workers can make suggestions. . a single high-end printer can be linked to the computer network and used by all. And when networked. A successful business is an organized business. any employee can retrieve the same files when needed. large projects are much easier to transfer than through email alone. Employees can share project schedules directly across the network and make changes appropriately. For example printers. It is also a better medium for collaboration as employees can pass files back and forth.

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