Sigram Schindler D. Altenkrüger Ute Flasche Juergen Schulze Michael Steinacker The OSA Project - Design and Formal Specification of an X.25 Based Open Transport Layer and its Protocols. 51-86 1979 conf/kivs/1979 Kommunikation in Verteilten Systemen db/conf/kivs/kivs79.html#SchindlerAFSS79