In this article we will discuss X-25, will make brief discussion on X-25, In last article we discuss about PPP.

X.25 is an ITU-T standard protocol suite for packet-switched wide area network (WAN) communication. An X.25 WAN consists of packet-switching exchange (PSE) nodes as the networking hardware, and leased lines, plain old telephone service connections, or ISDN connections as physical links.

X.25 Packet Switched networks allow remote devices to communicate with each other over private digital links without the expense of individual leased lines.

Three Layers of X.25: These three layers correspond to the three lower most layers of the ISO-OSI reference model. The physical layer takes care of the interface between a computer terminal and the link which attaches it to the packet switching node.

X.25 uses Virtual Connection to connect DTE to the network, data circuit-terminating equipment (DCE) is used. DCE devices are communications devices, such as modems. A PAD (packet assembler/disassembler) is used if a DTE is to simple (like character-mode terminals) to support the full X.25 functionality. 


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