INTERNET & WEB TECHNOLOGIES by Abhilash Sahoo 1 Internet and Web Technologies Chapter 1 | The Internet and WWW Internet A vast network of interconnected computer systems which permit users to communicate and share information. It is a network of networks that consists of millions of private and public, academic, business, and government networks of local to global scope that are linked by a broad array of electronic and optical networking technologies. The Internet carries a vast array of information resources and services, most notably the interlinked hypertext documents of the World Wide Web (WWW) and the infrastructure to support electronic mail. World Wide Web The World Wide Web is a system of interlinked hypertext documents contained on the Internet. With a web browser, one can view web pages that may contain text, images, videos, and other multimedia and navigate between them using hyperlinks. Hypertext Hypertext is text displayed on a computer with references (hyperlinks) to other text that the reader can immediately access, usually by a mouse click or keypress sequence. Apart from running text, hypertext may contain tables, images and other presentational devices. A hypertext document consists of non‐linear text with links to other text or documents. One navigates through hypertext by following the active links in the text. Hyperlinks A hyperlink, more commonly called a link, is an electronic connection between one web page to either (1) other web pages on the same web site, or (2) Web pages located on another web site. More specifically, a hyperlink is a connection between one pages of a hypertext document to another. Introduction: Web Architecture One of the greatest things about the Internet is that nobody really owns it. It is a global collection of networks, both big and small. These networks connect together in many different ways to form the single entity that we know as the Internet. In fact, the very name comes from this idea of interconnected networks. 2 Internet and Web Technologies The Internet: Computer Network Hierarchy Internet Service Provider (ISP) An Internet service provider (ISP, also called Internet access provider, or IAP) is a company or organization that has the equipment and telecommunication line access to provide connectivity to the Internet for customers. This is usually done for a set yearly or monthly fee. Point of Presence (POP) The POP is a place for local users to access the company's network, often through a local phone number or dedicated line. Every computer that is connected to the Internet is part of a network, even the one in your home. For example, you may use a modem and dial a local number to connect to an Internet Service Provider (ISP). At work, you may be part of a local area network (LAN), but you most likely still connect to the Internet using an ISP that your company has contracted with. When you connect to your ISP, you become part of their network. The ISP may then connect to a larger network and become part of their network. Most large communications companies have their own dedicated backbones connecting various regions. In each region, the company has a Point of Presence (POP). The amazing thing here is that there is no overall controlling network. Instead, there are several high‐level networks connecting to each other through Network Access Points or NAPs. 3 Internet and Web Technologies When you connect to the Internet, your computer becomes part of a network. DNS: Domain Name System When the Internet was in its infancy, it consisted of a small number of computers hooked together with modems and telephone lines. You could only make connections by providing the IP address of the computer you wanted to establish a link with. For example, a typical IP address might be 216.27.22.162. This was fine when there were only a few hosts out there, but it became unwieldy as more and more systems came online. The first solution to the problem was a simple text file maintained by the Network Information Center that mapped names to IP addresses. Soon this text file became so large it was too cumbersome to manage. In 1983, the University of Wisconsin created the Domain Name System (DNS), which maps text names to IP addresses automatically. This way you only need to remember www.example.com, for example, instead of example.com's IP address. URL: Uniform Resource Locator When you use the Web or send an e‐mail message, you use a domain name to do it. For example, the Uniform Resource Locator (URL) "http://www.example.com" contains the domain name example.com. So does this e‐mail address: [email protected]. Every time you use a domain name, you use the Internet's DNS servers to translate the human‐readable domain name into the machine‐readable IP address. Top‐level domain names, also called first‐level domain names, include .COM, .ORG, .NET, .EDU and .GOV. Within every top‐level domain there is a huge list of second‐level domains. For example, in the .COM first‐level domain there is: Google Yahoo Microsoft Every name in the .COM top‐level domain must be unique. The left‐most word, like www, is the host name. It specifies the name of a specific machine (with a specific IP address) in a domain. A given domain can, potentially, contain millions of host names as long as they are all unique within that domain. DNS servers accept requests from programs and other name servers to convert domain names into IP addresses. When a request comes in, the DNS server can do one of four things with it: 1 It can answer the request with an IP address because it already knows the IP address for the requested domain. 4 Internet and Web Technologies 2 It can contact another DNS server and try to find the IP address for the name requested. It may have to do this multiple times. 3 It can say, "I don't know the IP address for the domain you requested, but here's the IP address for a DNS server that knows more than I do." 4 It can return an error message because the requested domain name is invalid or does not exist. Internet Protocol Protocols Protocols (rules determining the format and transmission of data) are often text and simply describe how the client and server will have their conversation. Internet Protocol Suite The Internet Protocol Suite (commonly known as TCP/IP) is the set of communications protocols used for the Internet and other similar networks. It is named from two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were the first two networking protocols defined in this standard. Internet Protocol (IP) The Internet Protocol (IP) is a protocol used for communicating data across a packet‐switched internetwork using the Internet Protocol Suite, also referred to as TCP/IP. IP is the primary protocol in the Internet Layer of the Internet Protocol Suite and has the task of delivering distinguished protocol datagrams (packets) from the source host to the destination host solely based on their addresses. Transmission Control Protocol (TCP) The Transmission Control Protocol (TCP) is one of the core protocols of the Internet Protocol Suite. TCP provides a communication service at an intermediate level between an application program and the Internet Protocol (IP). That is, when an application program desires to send a large chunk of data across the Internet using IP, instead of breaking the data into IP‐sized pieces and issuing a series of IP requests, the software can issue a single request to TCP and let TCP handle the IP details. TCP is used extensively by many of the Internet's most popular applications, including the World Wide Web, E‐mail, File Transfer Protocol, Secure Shell, and some streaming media applications. File Transfer Protocol File Transfer Protocol (FTP) is a standard network protocol used to exchange and manipulate files over a TCP/IP based network, such as the Internet. FTP is built on client‐server architecture and utilizes separate control and data connections between the client and server applications. Applications were originally interactive command‐line tools with standardized command syntax, but graphical user interfaces have been 5 Internet and Web Technologies developed for all desktop operating systems in use today Hypertext transfer protocol (HTTP). A protocol (utilizing TCP) to transfer hypertext requests and information between servers and browsers. Hypertext Transfer Protocol (HTTP) is an application‐level protocol for distributed, collaborative, hypermedia information systems. Its use for retrieving inter‐linked resources, called hypertext documents. There are two major versions, HTTP/1.0 that uses a separate connection for every document and HTTP/1.1 that can reuse the same connection to download, for instance, images for the just served page. Hence HTTP/1.1 may be faster as it takes time to set up such connections. Request line, such as GET /images/logo.gif HTTP/1.1, which requests a resource called /images/logo.giffrom server Ports and HTTP Any server machine makes its services available using numbered ports: one for each service that is available on the server. For example, if a server machine is running a Web server and a file transfer protocol (FTP) server, the Web server would typically be available on port 80, and the FTP server would be available on port 21. Clients connect to a service at a specific IP address and on a specific port number. Once a client has connected to a service on a particular port, it accesses the service using a specific protocol.