What Is X.25 in Networking?

There are a myriad of networking protocols and standards, each serving its own unique purpose in the digital world. One such standard, often overlooked but undeniably significant, is the X.25.

What is X.25?

X.25, a protocol suite for packet-switched wide area network (WAN) communication, was developed by the International Telecommunication Union (ITU). The primary aim of X.25 is to provide an interface for connecting public data networks. It specifies procedures and protocols for establishing, maintaining, and terminating a connection, as well as for transferring data and network traffic.

History of X.25

The origin of X.25 traces back to the 1970s when it was conceived to be used over analog telephone systems. Back then, the digital revolution was just picking up pace. X.25 was among the first protocols to offer end-to-end connectivity by packaging data into packets before transmission. Despite the advent of more advanced technologies like Frame Relay, ATM, and more recently MPLS, X.25 has managed to hold its ground, particularly in industries where reliability outweighs speed.

How X.25 works

The workings of X.25 might seem complicated at first, but with a closer look, one can appreciate the elegance of its design. X.25 uses a virtual circuit approach to provide a bidirectional communication path between two devices.

The process begins with call setup, where the source and destination addresses are established. Once the call is accepted, data transfer begins. Data is divided into packets and each packet is assigned a sequence number to ensure correct order at the receiving end. The X.25 layer at the receiving end sends an acknowledgement for each received packet. Once the data transfer is complete, a disconnect call ends the session.


Despite the emergence of newer and faster protocols, X.25 remains relevant due to its simplistic design and high reliability. While it may not be the first choice for high-speed applications, it serves as a robust solution for industries that prioritize data integrity over speed.

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