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X.25 is a WAN communication standard used for dial-up internet service. It defines how users connect to the network and pay based on usage. The standard was adopted in the 1970s and is used by common carriers. It consists of three parts: data terminal equipment, data circuit-terminating equipment, and packet switched exchanges. Data transfer occurs through virtual circuits and segmented packets. X.25 was widely used in the 1980s but has been largely replaced by Internet Protocol.
X.25 is a standard for WAN (Wide Area Network) communication maintained by the International Telecommunication Union-Telecommunication Standardization Sector. Most commonly, it is used for dial-up Internet service. Defines how home users connect to the network and how those connections are maintained. Users generally pay for connected service based on how much they use it, just like an electricity or water bill.
The X.25 standard was adopted in the mid-1970s. It is most often used by common carriers, such as telephone companies using packet switched networks. As information moves through a packet-switched network, it is automatically split into packets of a particular size. Information is moved as a package even if the content and format of the various pieces are unrelated. A small number of packets can be moved at any one time, leading to slow processing times when there is high demand on the network.
A network that follows the X.25 standard consists of three basic parts. Data terminal equipment is the network hosts and personal computers that use the network. Data circuit-terminating equipment are modems and packet switches that allow computers to communicate with the network. Packet switched exchanges are the switches that actually transfer data across the network.
When a user wants to download something, the user’s computer sends a signal over the phone line and modem to the X.25 network. A packet-level protocol sets up a virtual circuit, which is basically a temporary connection between the user’s computer and the server or computer the user is downloading from. The connection request can be accepted or rejected. An X.25 network uses the X.121 address format to ensure that the virtual circuits it creates are among the correct components of the network.
The data requested by the user is then segmented into packets. These packets are sent over the X.25 network to the user’s computer at standard speed. The data is then “unzipped” for use on the user’s computer.
To process the packets created during data transfer, many computers rely on a packet assembler and disassembler. This device works between the computer and the modem. In addition to assembling and disassembling packages, it also stores packages until the device can process them. This is called buffering.
The X.25 standard was used extensively in the 1980s, primarily by telephone companies and for financial transactions. Some telephone companies still use the system. Most telecommunications companies have switched to Internet Protocol as it is simpler and does not suffer from the same traffic constraints.
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