X.25 PROTOCOL OPERATION RELATIONSHIP WITH THE OSI MODEL
FUNCIONAMIENTO DE PROTOCOLO X.25 Y SU RELACION CON EL MODELO OSI
(CON SUBTITULOS EN INGLES, ACTIVALOS EN LA CONFIGURACIÓN)
X.25 PROTOCOL OPERATION RELATIONSHIP WITH THE OSI MODEL
X.25 protocol
One of the most widely used protocols of the international telecommunications union that was originally approved in 1976 that has undergone various revisions since then.
This standard specifies an interface between a host system and a packet switched network, is used almost universally to interface with a packet switched network, and was used for packet switching in ISDN.
In x.25 each packet that is sent is confirmed between the computers that make up the network.
In x.25 communication is slow, good operation is ensured even with unreliable media, the standard uses three levels of protocols, physical level, data link, network level.
These three levels correspond to the three lowest layers of the OSI reference model, the physical level defines the physical interface between a station connected to the network and the link that links that station to a packet-switched node.
The link layer ensures the reliable transfer of data over the data link using a sequence of frames, the link layer standard is known as lap B.
The packet level offers an external virtual circuit service, this service allows any subscriber on the network to establish logical connections called virtual circuits with other subscribers.
The relationship that exists between the levels of x are:
User data is passed down to level three of x.25, which adds control information to it by creating a packet, alternatively user data can be segmented into multiple packets that serve various purposes.
Multiplexing in x.25
Perhaps the most important service that x.25 provides is multiplexing, a DTE can establish up to 4095 simultaneous virtual circuits with other DTEs, using a single physical link.