ISO/IEC 8885:1993/AMD9:1995

Information technology – Telecommunications and information exchange between systems – High-level data link control (HDLC) procedures – General purpose XID frame information field content and format – Amendment 9: Extension of HDLC sequence number modulus beyond 128

This amendment increases the modulus number (i.e. the sequence number) in steps up to a maximum of 2 147 483 648 which can be represented in 31 bits. This is done by the introduction of a new “Set Mode” command that can be used to negotiate or indicate the modulus in the absence of or to override a default value. This uses an optional information filed in the “Set Mode” command.