This Standard ECMA-60 describes the HDLC Unbalanced Class of Procedure for data transmission, using the Frame Structure described in Standard ECMA-40 and the Elements of Procedure defined in Standard ECMA-49.
This Class applies to point-to-point and multipoint configurations only, over either permanent or switched data transmission circuits. The characteristic of this class is the existence of one privileged station with a Primary function that bears an overall responsibility in link management. Hence the name Unbalanced Class of Procedure.
It is also recognized that it is possible to construct symmetrical configurations for operation on a single data transmission circuit from the class of procedure defined in this Standard.
For example, the combination of two Primary to Secondary links (with I frame flow as commands only) would create a symmetrical point-to- point configuration.