Internet and Computer Networks PDF

Internet: The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite (often called TCP/IP, although not all applications use TCP) to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, aca...

Internet: The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite (often called TCP/IP, although not all applications use TCP) to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of electronic, wireless and optical networking technologies. The Internet carries an extensive range of information resources and services, such as the inter linked hypertext documents of the World Wide Web (WWW) and the infrastructure to support email. Computer Networks A computer network is the infrastructure that allows two or more computers (called hosts) to communicate with each other. Definition A network can be defined as a group of computers and other devices connected in some ways so as to be able to exchange data. -Each of the devices on the network can be thought of as a node; each node has a unique address. 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. The network achieves this by providing a set of rules for communication, called protocols, which should be observed by all participating hosts. A communications protocol is a set of rules for exchanging information over a network The need for a protocol should be obvious: it allows different computers from different vendors and with different operating characteristics to 'speak the same language'. Properties of Computer Networks: 1 a) Facilitate communications. Using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing. b) Permit sharing of files, data, and other types of information. In a network environment, authorized users may access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks. c) Share network and computing resources. In a networked environment, each computer on a network may access and use resources provided by devices on the network, such as printing a document on a shared network printer. Distributed computing uses computing resources across a network to accomplish tasks. d) May be insecure. A computer network may be used by computer hackers to deploy computer viruses or computer worms on devices connected to the network, or to prevent these devices from normally accessing the network (denial of service). e) May be difficult to set up. A complex computer network may be difficult to set up. It may also be very costly to set up an effective computer network in a large organization or company. Why Networks a) Load Sharing: Both the program and data are transmitted to a remote computer to equalize the load between the two facilities. b) Message Service: A network can be used to handle interpersonal message transmissions. This type of service can also be used for educational services and conference activities. However, it is not an important motivation for a network of scientific computers. c) Data Sharing: The program is sent to a remote computer where a large data base exists. This type of operation will be particularly useful where data files are too large to be duplicated economically d) Program Sharing. e) Remote Service. Network Terminologies 1) Intranet: An intranet is a set of networks, using the Internet Protocol and IP-based tools such as web browsers and file transfer applications, that is under the control of a single administrative entity. That administrative entity closes the intranet to all but specific, authorized users. Most commonly, an intranet is the internal network of an organization. A large intranet will typically have at least one web server to provide users with organizational information. 2) Extranet: An Extranet is a computer network used outside the intranet. An extranet is a computer network that allows controlled access from the outside, for specific business or educational purposes. In a business-to business context, an extranet can be viewed as an extension of an organization\'s intranet that is extended to users outside the organization, usually partners, vendors and suppliers, in isolation from all other Internet users. 3) Local area network: A local area Network (LAN) is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network is a node. 2 4) Wide area network: A wide area Network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often uses transmission facilities provided by common carriers, such as telephone companies. 5) Enterprise private network: An enterprise private network is a network built by an enterprise to interconnect various company sites, e.g., production sites, head offices, remote offices, shops, in order to share computer resources. 6) 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.g., the Internet) instead of by physical wires. The data link layer protocols of the virtual network are said to be tunneled through the larger network when this is the case. One common application is secure communications through the public Internet, but a VPN need not have explicit security features, such as authentication or content encryption. VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features. Network topology: A network topology is the layout of the interconnections of the nodes of a computer network. Network topology signifies the way in which devices in the network see their logical relations to one another. The use of the term \"logical\" here is significant. That is, network topology is independent of the \"physical\" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via a hub, the network has a Star topology, rather than a bus topology. In this regard the visual and operational characteristics of a network are distinct; the logical network topology is not necessarily the same as the physical layout. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks. Common layouts are: 1) Bus Network: all nodes are connected to a common medium along this medium. 2) A star network: all nodes are connected to a special central node. 3) A ring network: each node is connected to its left and right neighbor node, such that all nodes are connected and that each node can reach each other node by traversing nodes left- or rightwards. 4) 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. 5) A fully connected network: each node is connected to every other node in the network. 3 History of Internet In the late 1950\'s the Advanced Research Projects Agency (ARPA) was founded in the United States with the primary focus of developing information technologies that could survive a nuclear attack. (Internet History) In 1967 ARPA university and private sector contractors met with representatives of the Department of Defense to discuss possible protocols for sharing information via computers. In 1969, the U.S. Defence Department funded a project to develop a network, which can withstand the bombing. Basically, the idea was to develop a very secure network which can work even after a nuclear attack. This project was known as ARPANET. The proposed network was not supposed to have a central control---which would be an obvious target. It connected four sites at the University of California at Los Angeles, the University of California at Santa Barbara, Stanford Research Institute, and the University of Utah. Throughout the 1970\'s researchers concentrated on developing protocols for controlling networks, moving messages across a system of networks, and allowing for remote access to the networks. There were computers connected at about two dozen sites when the first email was sent in 1972, but the number of sites and messages soon mushroomed. By 1975 there were 63 sites. Ten years of research brought Local Area Ethernet Networks (LANs) and workstations were developed to get connected to LAN. These workstations and LANs were then connected to the ARPANET. For next decade the ARPANET grew and its decentralized features helped its rapid expansion. Computers connected to ARPANET used a standard or rule to communicate with each other. This standard used by ARPANET is known as NCP (National Control Protocol). Protocol is a network term used to indicate the standard used by a network for communication. But the passing time and rapid change in information technology suppressed NCP and brought TCP/IP (Transmission Control Protocol/Internet Protocol) in to the world of networking. TCP \"converts messages into streams of packets at the source, and they are reassembled back into messages at the destination. IP handles the dispatch of these packets. It handles the addressing, and makes sure that a packet reaches its destination through multiple nodes and even across multiple networks with multiple standards. This flexibility of TCP/IP to handle multiple networks with multiple protocols encourage other networks to get connected to ARPANET. Slowly the ARPANET became a massive network of networks and now it is known as 'Internet'. 4 The Internet has revolutionized the computer and communications world like nothing before. The invention of the telegraph, telephone, radio, and computer set the stage for this unprecedented integration of capabilities. The Internet is at once a world-wide broadcasting capability, a mechanism for information dissemination, and a medium for collaboration and interaction between individuals and their computers without regard for geographic location. The Internet represents one of the most successful examples of the benefits of sustained investment and commitment to research and development of information infrastructure. Commercial Development In 1963 during the early days of computers and six years before ARPANET, students at MIT developed the first computer game called Space War. It would be twenty years before the TCP/IP protocol stimulated the growth of various networks and nearly thirty years (1991) before the United States government opened the Internet to private enterprise (BBN Timeline), but this game foreshadowed the commercialization of the Internet. In the 1970\'s and 80\'s people who were online put out information about furniture and cars they wanted to sell. Debates raged about whether this was an appropriate use of the new research tool, the Internet, but when the Commercial Internet Exchange (CIX) was formed in 1991 the genie would not go back in the bottle. Commercial contractors have been involved in the development of ARPANET from its inception. As Tang and Teflon began as curiosities of the space program and later became common consumer products, so too have email, web research, and home shopping on the Web. It has only been ten years since the first relay between a commercial entity (MCI Mail) and the Internet was made. Since that time technologies have emerged that have fueled the growth of private enterprise on the Web. In 1992 Paul Linder and Mark McCahill at the University of Minnesota released Gopher, a tool that allowed researchers to retrieve specific data from myriad 8 locations. The next year Mosaic, a web browser, was developed at the University of Illinois by Netscape founder Marc Andreesen, the World Wide Web became a public the identification in-terms of User Login name and password of the FTP client. If one does not have an account in the remote FTP server, still he can connect to the server using anonymous login. Using anonymous login anyone can login in to a FTP server and can access public file archives, anywhere in the world, without having an account. One can easily Login to the FTP site with the username anonymous and e-mail address as password. The basic objectives of FTP are to give flexibility and promote sharing of computer programs, files and data to transfer data reliably and more efficiently over network to encourage implicit or indirect use of remote computers using Internet to shield a user from variations in file storage systems among hosts. The basic steps in an FTP session are: Start up your FTP client; by typing ftp on your system's command line/'C\>' prompt (or, if you are in a Windows, double-click on the FTP icon). Give the FTP client an address to connect to. This is the FTP server address to which the FTP client will get connected 5 Identify yourself to the FTP remote site by giving the Login Name Give the remote site a password Remote site will verify the Login Name/Password to allow the FTP client to access its files Look directory for files in FTP server Change Directories if required Set the transfer mode (optional); Get the file(s) you want; and Quit. Telnet (Remote Computing) Telnet or remote computing is telecommunication utility software, which uses available telecommunication facility and allows you to become a user on a remote computer. Once you gain access to the remote computer, you can use it for the intended purpose. The TELNET works in a very step by step procedure. The commands typed on the client computer are sent to the local Internet Service Provider (ISP), and then from the ISP to the remote computer that you have gained access. Most of the ISP provides facility to TELNET into your own account from another city and check your e-mail while you are travelling or away on business. The followings steps are required for a TELNET session Start up the TELNET program; Give the TELNET program an address to connect to (some really nifty TELNET packages allow you to combine steps 1 and 2 into one simple step!); Make a note of what the \"escape character\" is; Log in to the remote computer; Set the \"terminal emulation;\" Play around on the remote computer; and Quit. WORLD WIDE WEB (WWW) WWW is the acronym for the World Wide Web. It is also commonly known as 'The Web'. The WWW is a system that we use to access the Internet. The WWW is hypertext-based information retrieval tool, it uses the hypertext to access the various forms of information available on the world's different networks. One can easily surf the Web by jumping from one document to another using the links in those documents. These documents can be in many formats, such as text, graphics, animation, sound and latest is video. They may also be a combination of all these. All the information on Internet is presented to the user as a document or more popularly known as Web Page. All these Web Pages are link to each other or even to section within a Web Page. The Web Concepts 6 The Web was developed to be a pool of human knowledge, and human culture, which would allow collaborators in remote sites to share their ideas and all aspects of a common project. The Web consists of a vast assortment of files and documents that are stored on these computers and written in some form of Hyper Text Markup Language (HTML) that tells browsers how to display the information. The computers that store the files are called servers because they can serve requests from many users at the same time. Users access these HTML files and documents via applications called browsers. The main Web concepts are: Web Page The Web page is a space of information on the Internet that presents information about a particular person, business, or organization or cause. The Web consists of files, called Web pages (documents). It is containing links to resources (text, images, audios, videos, and other data), throughout the Internet Web Site Web site can be defined as a collection of web pages which are grouped together and usually connected together in various ways. Often called a \"web site\" or simply a \"site.\" The web site usually presents information about a particular person, business, organization or cause. Generally, there are two types of website styles, Static and Dynamic website: A static Website is one that has web pages stored on the server in the same form as the user will view them. A dynamic Website is one that does not have web pages stored on the server in the same form as the user will view them. Instead, the web page content changes automatically and/or frequently based on certain criteria. There are two meaning for dynamic website. The first is that the web page code is constructed dynamically, piece by piece. The second one is that the web page content displayed varies based on certain criteria. The criteria may be pre-defined rules or may be based on variable user input. The Web Terms Uniform Resource Locator (URL) It is the complete address of World Wide Web page and consists of three components that identifies where the web page is stored on the Internet. These parts are: the protocol, the site name, and the absolute path to the document or resource as shown in the following example 7 protocol name (e.g., HTTP) http:// The first thing the URL does is define the protocol that will be used for that particular transaction. The letters HTTP let the server know to use Hypertext Transfer Protocol, or get into "web mode." domain name/ hostname (servers address that a user wants to connect with), for example, www.google.com. www.example.com The next portion of the URL identifies the website by its domain name. In this example, the domain name is example.com. The "www." part at the beginning is the particular host name at that domain. For example, there might also be development.example.com, clients.example.com, and so on. File name is optional, implies the access to a file/directory into the principal webpage. /2012/samples/first.html This is the absolute path through directories on the server to the requested HTML document, first.html. The words separated by slashes are the directory names, starting with the root directory of the host. Example: http://www.icci.org/studies/ips.html. 1. Protocol: http. 2. Host computer name: www. 3. Second-level domain name: icci. 4. Top-level domain name: org. 5. Directory name: studies. 6. File name: ips.html. Several Top-level domain are common: com: commercial enterprise. edu: educational institution. gov: government entity. mil: military entity. net: network access provider. org: usually nonprofit organizations biz: Businesses pro: Professionals, such as doctors and attorneys Web hosting After we create a website, it is necessary to store it in a place where it is always available for users. We use Web hosting services/companies for this purpose. They own web servers that have the ability to store content. Search engine Search engines allow us to search in the Internet for information, images and other types of files stored in various locations available throughout the network. Search engines work according to certain algorithms that show the user relevant, requested search results. At first, information from the various websites is collected and stored and then analyzed to organize and save them in the database for future use. When a user enters an inquiry into the search engine, the database is organized by an index and the user is presented with results that 8 match best the entered search terms. Therefore, it is important to understand that by using the search engine one does not search the entire Internet but the search engine's database. Therefore, we might get different results each time we use different web engines. 4. Internet protocols TCP/IP protocol: TCP / IP: This protocol is the main protocol for Internet communication. It defines the rules that computers need to follow to communicate with other computers via a network. HTTP (Hypertext Transfer protocol): is a network protocol that ensures the exchange of almost all types of resources on the web. With resources, we mean files, pages, images, search results, etc. It is basically, the web browsers language to send requests to the server. There is also the HTTPS version, which is a secure and encrypted version for HTTP communications. FTP (File Transfer Protocol): is used to load (upload) or retrieve (download) files between the client and server communication, or between two computers on the Internet. In other words, this protocol is responsible for file transfer on the Internet. Internet Service Provider (ISP):Is an organization that provides individuals and other companies' access to the Internet and other related services such as e-mail. Web Design: Client-Server Architecture 1. Client-Server Architecture Computers on the Internet use client/server architecture. This means that the remote server machine provides files and services to the user local client machine. Web Server: A Web Server is a computer purposed to runs special serving software. That software \"serves\" HTML pages and the files associated with those pages when requested by a client, usually a Web browser. The computer is secured so that only authorized people can access it to make changes to the data, so, If a person is on the same network as the Web Server, he or she may be able to save the data directly onto the Web Server computer (if authorized). Server-side: JSP (Java Server Pages) ASP (Active Server Pages) 9 ASP.NET (next generation of ASP) PHP Phython Client: The Client (front end) or user side of the Web, it typically refers to the Web browser in the user\'s machine. It may also refer to plug-ins and helper applications that enhance the browser to support special services from the site. The term may imply the entire user machine or refer to a handheld device that provides Web access. Client-side: HTML / XHTML (Extensible Hyper Text Markup Language) CSS (Cascading Style Sheets) JavaScript / VBScript (client-side scripting). Web Browsers: Generally, a web browser is a software application or program for retrieving, displaying, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier (URI) and may be a web page, image, video, or other piece. 10