This Standard is applicable to the interconnection of data terminal equipment (DTE) and data circuit-terminating equipment (DCE) employing serial binary data operation via the ITUT Recommendation V.24, 100-series interchange circuits. This Standard, through reference to ITU-T Recommendation V.250, provides four elements: -- codifies existing practice in common asynchronous DCE that use the AT command set. It identifies the protocol elements procedures, and behaviors that were found to be held in common among a large portion of DCE manufacturers; -- defines a format for extension of the AT command set in an orderly fashion. It reserves the "+" command prefix to be used by other standardized extensions; -- provides a set of standardized extensions, based on the extended "+" command format.