scope:

This International Standard describes elements of data link control procedures for synchronous bit sequence independent data transmission using the HDLC frame structure (see ISO 3309¹⁾) and independent frame numbering in both directions.

These HDLC elements of procedures are described specially in terms of the actions that occur on receipt of commands at a secondary.

This International Standard is intended to cover a wide range of applications, for instance, one-way, two-way alternate or two-way simultaneous data communication between DTE's which are usually buffered, including operations on different types of data circuits, for example, multipoint/point-to-point connections, duplex/half-duplex transmission, switched or non-switched, etc.

The defined HDLC elements of procedures are to be considered as a common basis for establishing different types of control procedures. This International Standard does not define any single system and should not be regarded as a specification for a data communication system. Not all the commands or responses, respectively, might be required for a particular system implementation.

A DTE intended to be operated within the constraints of this International Standard provides a high degree of compatibility, if it implements all features of the stipulated class of operation as specified in other HDLC standards.

¹⁾ ISO 3309, Data communication - High level data link control procedures - Frame structure.