An architecture model and a subset of a behavior model of the ISO virtual terminal (VT) are specified in the formal description technique Estelle. The architecture model includes modules and their appropriate interconnections (channels) for a VT-user, a VT protocol machine (VTPM), an association control service entity (ACSE), autonomous-abort internal events, a presentation layer element, and a mapping machine to map protocol data units of the VTPM onto service primitives of the ACSE and the presentation layer. The behavior model specifies the association establishment phase of the VTPM for the synchronous mode of operation, assuming that no optimal function units are selected. The combination of VT and Estelle represents ISO's effort toward implementing the Open Systems Interconnection (OSI) model.>