Internet

In IT, the global computer network and the related services that can be accessed, via Modem connected to a public telephone line, and a computer or PC, by any user (private or organization) by subscription with a service company (Provider , ISP), through access points (Point Of Presence, POP), which takes care of the connection between the user and the rest of the network. This network consists of countless sites, portals, physical networks and nodes around the world, which can exchange data with packet-switched techniques using the TCP / IP protocol (Transmission Control Protocol / Internet Protocol). The sites represent virtual locations of subscribers, identified by a specific address (URL: Uniform Resource Locator), in which information is available for those who access the address. The most typical services are consultation and interaction with databases and use of electronic mail (electronic mail, e-mail, V.). The set of links between various sites and information resources create the so-called World Wide Web (WWW or synthetically the “Web”, web), a network extended to the whole world, in which it is possible to move from one site to another using appropriate tools connection and software search programs (“browser”). These programs allow the exploration or so-called surfing between the sites, as well as the acquisition of written documents with HTML (Hyper Text Markup Language) and XML (Extended Markup Language, V.) languages, by means of HTTP hypertext transfer protocol (Hyper Text Transfer Protocol). Internet access via the traditional telephone line takes place at the maximum nominal speed of 56 kbps (on average 33 kbps), connections are also possible at 64-128 kbps and at 640/128 kbps, respectively with ISDN and ADSL technologies, always on the traditional telephone line. To access the Internet, via a modem, in addition to the traditional telephone line, the computer can be connected to the cellular telephone network (GSM) at 9.6 kbps, or at higher speeds with the relevant upgrade standards: HSCSD at 43 , 2 kbps, GPRS at 115 kbps, EDGE at 384 kbps. Access is also provided with the new UMTS and LMDS standards at 2 Mbps and beyond in development. Internet access is available without a computer and modem; it is also possible with only the mobile phone (GSM) using WAP (Wireless Application Protocol) technology which, via a WAP gateway of the cellular network manager, interconnects with the Internet. Access to information resources and application services can be public or linked to the recognition of keywords (passwords). In the railway sector, Internet technology is spreading in particular with regard to information services, timetables, commercial transactions and data exchange between operators and companies. In circulation systems, the use of hypertextual browser techniques finds applications for access to the manual, databases, operator guide, etc