This part of ISO/IEC 9041 specifies: a) a set of procedures for the connection-oriented transfer of data, control and reference information between protocol machines which implement the functions of a provider of the Basic Class Virtual Terminal Service; b) the two modes in which those procedures operate; c) the structure of protocol elements used for the transfer of data and control Information and the mapping of these protocol elements onto ACSE and lower layer services; d) the means of negotiating the functional units to be used by the protocol machines and the parameters of the service; e) the structure and mapping of protocol elements used for the transfer of data and control information. The procedures are defined in terms of: f) the interactions between Virtual Terminal Protocol Machines through the exchange of Virtual Terminal protocol elements; g) the Interactions between a Virtual Terminal Protocol Machine and the Virtual Terminal service user in the same system through the exchange of Virtual Terminal service primitives; h) the interactions between a Virtual Terminal Protocol Machine and the ACSE and Presentation Service providers through the exchange of service primitives. This part of ISO/IEC 9041 also specifies conformance requirements (see clause 13) for systems implementing these procedures. It does not contain tests which can be used to demonstrate this conformance. These procedures are applicable to instances of communication between systems that support the Basic Class Virtual Terminal Service in the Application Layer of the Reference Model for Open Systems Interconnection and which wish to interconnect in an open systems environment.