ECMA-49

This Standard ECMA-49 defines in detail the Elements of Data Link Control Procedure for bit sequence independent data transmission using the Standard ECMA-40, Frame Structure, and frame numbering in both directions.

These HDLC Elements of Procedure are defined specifically in terms of the actions that occur on receipt of commands at a Secondary or Combined.

This Standard is intended to cover a wide range of applications, for instance, one way, two way alternate or two way simultaneous information transfer between stations which are usually buffered, including operations on different types of data circuits, e.g. multipoint/point-to-point configurations, duplex/half duplex facilities, switched/non-switched services.

In HDLC procedures, the normal cycle of the code transparent data communication between two data stations consists of the transfer of frames containing information from the data source to the data sink, acknowledged by frames in the opposite direction. Until the station receives an acknowledgement, it must hold the original information in memory in case a retransmission is necessary.

The basic configurations of stations are specified indicating how Secondaries are responsible to a Primary and how Combined’s are responsible to each other.

Implementation of a particular system will normally require only a limited selection of commands and responses. Equipment designed for particular systems may not implement all the commands and responses defined in this Standard.