Internet and Web-based network
Web applications run on the World Wide Web (Web, World Wide Web, WWW, Web). Initially, the Web-based network was considered an information system designed for the collective work of users with hypertext documents (HTML pages) located on the Internet. Currently, the Web-based network is already being considered as a platform on the basis of which various applications and complex information systems are developed. In turn, the WWW is one of the services that operates on the Internet. The interrelation of web-applications with WWW and Internet networks, as well as the protocols used in them, is shown in Fig. 1.1.
Fig. 1.1. Interconnection of web applications with other technologies
In this regard, before considering the development of web-applications, you should consider the basic concepts of the Internet and Web-based networks.
Internet (Internet) is the worldwide network of computers and various devices for storing and transferring data. This network appeared in 1969, when the first transfer of data between the computers of the University of California Los Angeles and the Stanford Research Institute (distance - 640 km.). By June 30, 2012, the number of users who regularly use the Internet amounted to more than 2.4 billion people (more than a third of the world's population).
Basic Internet Concepts
The Internet includes:
• Infrastructure - high-speed data transmission channels, special computers that control the transfer of data packets (routers) and special software;
• A large number of connected computers and various devices with server and client software.
All the Internet software runs on the "client-server" technology, that is, the programs used are divided into two types:
• servers - passive programs that wait for requests from users, process them, generate a response and send it to the user.
• Clients - are the active programs that network users normally use on their computers. They send requests to servers for some work (usually getting information).
For the interaction of clients and servers, it is necessary to follow the same rules for the description of queries and responses to them. These sets of rules are called data transfer protocols . The baseline of the Internet operates using two main Internet Protocol (IP) and Transmission Control Protocol (TCP) protocols, often referred to jointly , such as TCP/IP. They allow you to transfer data in the form of specially designed packages of limited size. Working with the IP and TCP protocol is usually supported at the level of the operating system. Currently, two versions of the IP protocol are used: the fourth version (IPv4) and the sixth version (IPv6).
All devices (including computers) connected to the Internet are assigned unique digital addresses, called IP addresses, which are whole 4-byte (unsigned) numbers (for IP-protocol version 4) or 16-bit byte (unsigned) numbers (for IP protocol version 6). For convenience, IP addresses are written as a sequence of values for each byte, separated by the symbol & quot;. & Quot ;. For example, 184.108.40.206.
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