Automated Validation of a Communications Protocol: the CCITT X.21 Recommendation
Colin H. West, P. Zafiropulo · IBM Journal of Research and Development · 1978
The call establishment procedure of the X.21 interface recommended by the International Telegraph and Telephone Consultative Committee (CCITT) has been validated as a test of a recently developed theory and of an implemented system for automated communications protocol validation. The test demonstrated the applicability of the validation technique and identified a number of points where the interface state diagram does not completely define the interface behavior.