ISO/IEC 3309:1993

Specifies the frame structure for data communication systems using bit-oriented high-level data link control (HDLC) procedures. Defines the relative positions of the various components of the basic frame and the bit combination for the frame delimiting sequence (flag). The mechanisms used to achieve bit pattern independence (transparency) within the frame are also defined. In addition, two frame checking sequences (FCS) are specified, the rules for address field extension are defined, and the addressing conventions available are described.