This Standard ECMA-61 describes the HDLC Balanced 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 is specially intended for operation on point-to-point links over either permanent or switched data transmission circuits. The characteristic of this class is that both stations have equal responsibilities and rights for link management. Hence the name Balanced Class of Procedure.
Stations capable of operating in this way are called Combined because they combine the properties of Primary and Secondary functions. In balanced operation the link consists of Combined operating in asynchronous balanced mode (ABM). A basic set of functions is defined, which can be modified by means of optional functions.
It is the intention that this Standard should be compatible with the ISO Balanced Class of Procedure. The ISO Standard was developed in conjunction with CCITT and the conformity with CCITT X.25 LAP B is identified in this Standard.