scope:

General

The concept of Profiles for OSI, and the structure of the International Standardized Profiles that document them, are defined in ISO/IEC TR 10000- 1. Such Profiles are divided into a number of different classes and sub-classes. Two of these classes contain sub-classes comprising functions of the Virtual Terminal Basic Class Service and Protocol specified in the base standards ISO 9040 and IS0 9041. These are the Application Profiles (A-Profiles) and the Interchange Format and Representation Profiles (F-Profiles).

The relationship between A-Profiles and FProfiles is described in 7.3.2 of ISO/IEC TR 10000-1 and is as follows. Application Layer base standards require, implicitly or explicitly, the structure of information carried or referenced by them to be specified for each instance of communication. It is the purpose of F-Profiles to specify such information structures. Particular functional requirements may then be met by the combination of an A-Profile with one or more F-Profiles.

Establishment of a VT-association involves the selection by negotiation of a particuiar Virtual Terminal Environment profile (VTE-profile), and of particular values for any arguments of that VTE-profile. The VTE-profile specification, and possibly also the values of certain VTE-profile arguments, may in turn reference the definitions of VT control object types and assignment types. These VTE-profiles, control object types and assignment types are therefore Information Objects that require explicit reference within the VT protocol.

Particular instances of these Information Objects are fully defined within the base standards, but the base standards also provide for further instances to be defined by registration. Each registered instance constitutes an F-Profile within the framework of ISO/IEC TR 10000.

The Virtual Terminal Basic Class Service and Protocol may be used to realize a wide range of distinct functions. Particular functions may be realized through the selection of appropriate VT functional units, F-Profiles and other VTE-profile argument values. The specification of the selection required to realize a particular function and to promote interoperability constitutes a Virtual Terminal A-Profile within the framework of ISO/IEC TR 10000.

The three International Registers of VT information structures and the specifications of VT Application Profiles are each published' as a separate multi-part ISP as follows:

- ISO/IEC ISP 11184 is the Register of VTE-profiles;

- ISO/IEC ISP 11185 is the Register of control  object type definitions;

- ISO/IEC ISP 11186 is the Register of assignment type  definitions;

- ISO/IEC ISP 11187 contains the specifications of VT Application Profiles.

This part of ISO/IEC ISP 11187 is applicable to environments in which a terminal population requires access to application packages running on a variety of computers. It may be used where the connection between the terminal and the computer that hosts the application package is  local, is made across a Local or Wide Area Network, or is made across a concatenation of such networks.

This part of ISO/IEC ISP 11187 contains the specification of the A-mode Generalized Telnet Application Profile. Virtual Terminal implementations that operate in accordance with this A-profile provide powerful general-purpose terminal capabilities which are suitable in particular for TELNEiT emulation. This A-profile specifies a mode of operation of, and a selection of options for use wiîh, the A-mode Generalized Telnet VTE-profile FVT115. These are together designed to provide versatility and to promote interoperability between Virtual Terminal implementations which support that VTE-profile.

This part of ISO/IEC ISP 11187 also specifies a Profile ICs proforma for the A-mode Generalized Telnet Application Profile specified herein in compliance with the relevant requirements, and in accordance with the relevant guidance, given in ISO/IEC [DIS] 9646-7. The supplier of an implementation which is claimed to conform to ISÖ/IEC ISP 11187-5 is required to complete a copy of the Profile ICS proforma as specified in 5.2 and is required to provide the information necessary to identify both the supplier and the implementation.

Position within the taxonomy

The taxonomy of international Standardized profiles for OSI is laid down in ISO/IEC TR 10000-2. Within the classification scheme of this International Standardized Profile are in the taxonomy, the OSI Profiles specified in this Virtual Terminal subclass of the class of Application Profiles.

A Profile within this subclass has a Profile identifier of the form AVTab, where ab is a structured numerical identifier that identifies the position of the Profile within two levels of subdivision of the subclass. The value of a is a single digit but is an integer that is not necessarily a single digit.

In principle the ISO Virtual Terminal model allows for multiple classes of operation, although at the time of publication of this International Standardized Profile only the Basic Class has been defined. The value of the identifier component a distinguishes between the permitted modes of operation of the Virtual Terminal Service as follows:

- a = 1 for Basic Class A-mode ( asynchronous mode );

- a = 2 for Basic Class S-mode (synchronous mode ).

Values greater than 2 are reserved for future developments.

ISO/IEC ISP 11187 contains the specifications of the Profiles with identifiers of the form AVT1b and AVT2b. The component b distinguishes between different Application Profiles that make use of the same mode of operation.

This part of ISO/IEC ISP 11187 contains the specification of the Application Profile with the Profile identifier:

AVT16 - A-mode Generalized Telnet Application Profile.

Scenario

The VT Basic Class Service is defined in ISO 9040. It operates within the OSI Reference Model defined in ISO/IEC 7498-1 to provide facilities for interactive terminal-oriented communication between two application- processes. The aspects of an application-process that make use of these facilities Constitute a VT-user as defined in ISO 9040. Figure 1 illustrates the elements of the OSI model that are concerned with communication between two VT-users in accordance with a VT Application Profile

The VT-user component of an applicationprocess (AP) communicates by invoking an application-entiîy (AE) to establish a VT-association with an application-entity of a peer application-process. In order to provide the VT Basic Class Service to their VT-users, two AEinvocations (AEIs) exchange information by means of both the VT Basic Class Protocol specified in ISO 9041-1 and the ACSE Protocol specified in ISO 8650. The VT Basic Class Service enables the VT-users to exchange data that may include control information related to virtual terminal functions and to real devices.

In the model of the OSI Application Layer given in ISOAEC 9545 the AE is a composition of two application-service-elements (ASEs)and a Control Function (CF). It is the CF that provides the VT Service to the VT-user. The ASEs are the VT ASE and the ACSE. in an AEI the CF provides the functions of the VT Service by making coordinated use of the services provided to it by invocations of each of the two ASEs. Each ASE-invocation (ASEI) in turn provides its services by an exchange of APDUs with its peer, for which it requires the use of the Connection-oriented Presentation Service. These requirements of the two ASEIs are passed to the CF, which coordinates them and makes the actual use of the Presentation Service.

An AEI operates in accordance with rules determined by an application-context. The definition of the application-context for a VTassociation is provided by clause 11 of ISO 9041-1

A VT Application Profile specifies constraints on the operation of an AEI within the applicationcontext defined in ISO 9041-1. It also specifies constraints on the use of the Presentation Layer by such an AEI and on the consequent use of the Session Layer by the Presentation Layer. A VT Application Profile is intended to be used in conjunction with any Truisport Profile (T-Profile) of ISO/IEC TR 10000-2 that provides a connection-mode Transport Service for use by the Session Layer.

A VT Application Profile may also specify constraints on the exchange of control information between the VT-users and on the behavior of a VT-user in response to information exchanged.

An AP-invocation may make concurrent or consecutive use of more than one AE-invocation. An AE-invocation may be a partner in one or more application-associations, either concurrently or consecutively. A VT-association is an application-association capable of supporting communication between two VT ASEs.

The VT Application Profiles specified in ISO/IEC ISP 11187 are concerned solely with the operation of a VT- association. They place no constraint on any other application-associations of the AE-invocation concerned or on any other AE-invocation belonging to the AP-invocation concerned.

The VT Application Profile speciñed in this part of ISO/IEC ISP 11187 assumes a relationship between the two communicating end systems described below. One end system ( the keyboard side ) assumes an initiator function and the other side assumes the responder function ( the application side ). These two devices form part of the VT-user component of that end system and are modelled within the data structures of the VT Service.