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ECMA-71

HDLC selected procedures

1st edition, January 1981

High Level Data Link Control Procedures (HDLC) are designed to cover a wide range of applications, e.g. TWA or TWS communication between computers, concentrators and terminals, as a wide range of data link configurations, e.g. multipoint or point-to-point, switched or non-switched.

Standards ECMA-40 and ECMA-49 define frame formats, operational modes, commands, responses and exception recovery techniques. These functions used in various combinations provide the full range of HDLC capability.

The majority of HDLC implementations will not require the full range of capability. Subsequent ECMA Standards have therefore defined certain selections of these functions for specific types of application.

Standard ECMA-60 defines a Class of HDLC Procedure using the Unbalanced modes of operation (UNR or UAR) and certain optional functions. Selected procedures 1 and 2 in this Standard ECMA-71, are specific implementation within this Unbalanced Class.

Standard ECMA-61 defines a Class of HDLC Procedure using the Balanced mode of operation (BA) and certain optional functions. Selected Procedure 3 in this Standard ECMA-71 is a specific implementation within this Balanced Class.

The Selected Procedures in this Standard are expected to meet the majority of requirements in the immediate future. They contain no optional features for user selection, so that conformance with them can be precisely and simply achieved.

Additional Selected procedures may be defined to meet any additional requirements as they are identified.

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