X.25 Interface and End-to-End Virtual Circuit Service Characteristics

Public packet switching networks around the world use CCITT Recommendation X.25, which is the standard device-independent interface between packet networks and user devices operating in the packet-mode. Since its development in 1976 and with four years of network operational experience, the X.25 interface specification has reached a high level of maturity. A revised version of X.25 has been approved by CCITT Study Group VII at its meeting in February 1980. The revised X.25 specification is more complete than its predecessor, eliminates a number of ambiguous areas which lead to network implementation differences, and has been enhanced by the addition of new capabilities both to the X.25 interface and to the end-to-end service. This paper presents a consolidated view of the end-to-end characteristics of the virtual-circuit-based services accessible through the X.25 interface. It then discusses the characteristics of the revised X.25 interface, with emphasis on areas that have been addressed in the revised Recommendation. The revised Recommendation leads the way to greater commonality among network implementations. The increased functionality of the end-to-end virtual-circuit services has impact on the relationship of X.25 to system architectures being discussed by international standards bodies.