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(protocol, standard)
An ITU-T standard protocol suite for the DTE-DCE interface in a packet-switched network, approved by ISO. X.25 defines standard physical layer, data link layer and network layers (layers 1 through 3). It was developed to describe how data passes into and out of public data communications networks. X.25 networks are in use throughout the world.

Document: ISO 8208.

Several other ITU-T recommendations are relevant to packet switching: X.3, X.28, X.29, X.75.


The first international standard packet switching network developed in the early 1970s and published in 1976 by the CCITT (now ITU). X.25 was designed to become a worldwide public data network similar to the global telephone system for voice, but it never came to pass due to incompatibilities and the lack of interest within the U.S. It has been used primarily outside the U.S. for low speed applications (up to 56 Kbps) such as credit card verifications and automatic teller machine (ATM) and other financial transactions. It has also been used for signaling networks in first-generation cellular systems.

X.25 provides a connection-oriented technology for transmission over highly error-prone facilities, which were more common when it was first introduced. Error checking is performed at each node, which can slow overall throughput and renders X.25 incapable of handling real-time voice and video.

In the U.S., leased T1 lines were favored for internetworking offices together rather than public data networks. However, frame relay, which was modeled after X.25, has been successful as a public data network technology for meeting the high bandwidth demands of today's organizations. See packet switching, frame relay and SMDS.
References in periodicals archive ?
28kg X25 convertible backpack is on sale now and again offers the brand's trademark 'back-to-front' security.
A revised timetable will be introduced for services 225 and X25 between Brighouse, Clifton, Cleckheaton and Leeds with two new X25 trips from Leeds.
Go North East service X25 and Gateshead Central Taxis/Stanley Travel service 23 will operate as follows: Service 23 will divert from Springwell Village via Springwell Road past the Bowes Railway to Wrekenton.
Summary: Routes 17, 32C, 367, C7, F1, F10 and X25 are being upgraded.
and a tri-cluster design, similar to the Helio X20 and X25, plus it is built
The Redmi Pro also sports 4GB of RAM, 128GB storage and MediaTek's Helio X25 SoC.
Thomas was caught on CCTV getting off the Stagecoach X25 bus on Moss Road, near Oak Road, at 6:23pm on July 2.
According to BAIC's website, only three models are for sale which include the compact D20, which is offered in both hatchback and sedan versions, and the X25, a small crossover based on the D20.
The Meizu PRO 6 is the first phone to ship with the MediaTek Helio X25, packing ten ARM CPU cores in three different groups.
Routes F24, 81 and X25 will join the service from September 1, along with several other routes that have been modified to enhance the service.
Her visit to her husband's former school and its young football team marked the launch of the new X25 service travelling from Langley Park and Newcastle.
Lane Community College reviewed seat and room utilization data obtained through X25 on its Main Campus, focusing on reviewing and resolving classroom demand issues during the prime time of 10:00 a.