X.25
X.25 is a standard protocol suite for packet-switched wide area network (WAN) communication, developed in the 1970s by the International Telecommunication Union (ITU-T). Here are detailed aspects regarding its history, functionality, and relevance:
History
- X.25 was developed to provide a common interface for connecting public and private data networks, enabling data transmission between different systems.
- Its development began in the late 1960s, influenced by the work of Donald Davies on packet switching at the National Physical Laboratory in the UK, and by the efforts of the ARPA with the ARPANET.
- The first version of the standard was published in 1976, with subsequent revisions in 1980, 1984, and 1988.
- X.25 was widely adopted for connecting remote terminals to central computers, especially in banking and government sectors due to its reliability and error correction capabilities.
Protocol Structure
- Physical Layer (Layer 1): Defines the physical means of connecting to the network, such as electrical, mechanical, procedural, and functional interfaces. It typically uses EIA RS-232, V.35, or X.21 standards.
- Link Layer (Layer 2): Known as LAPB (Link Access Procedure, Balanced), it provides error-free transmission over the link. It uses techniques like frame sequencing, acknowledgment, and retransmission to ensure data integrity.
- Network Layer (Layer 3): Manages the connection setup, routing, and termination. It includes:
- Call establishment, data transfer, and call clearing.
- Flow control and congestion control to manage network load.
Applications and Usage
- X.25 was predominantly used for:
- Connecting remote terminals to mainframes or minicomputers.
- Interconnecting different types of networks.
- Supporting applications like electronic funds transfer, credit card verification, and airline reservation systems.
- Despite being overtaken by newer protocols like Frame Relay and ATM due to speed and efficiency, X.25 remains in use for some legacy systems and in regions where its reliability is still valued.
Relevance Today
- While not commonly used for new deployments, X.25 is still employed in specific niches due to its:
- Robust error checking, which is beneficial in noisy environments or over long distances.
- Compatibility with older systems where upgrading might be cost-prohibitive.
External Links
See Also