Covers asynchronous data transmission with half duplex and duplex link protocols operating with window size one for message transfers. Specifies standards on coding, formatting and synchronizing data frames of variable and fixed lengths which meet specified data integrity requirements.Cross References:BS 7404:Section 1.1BS 7404:Section 5.2ISO 3309IEC 50(371)IEC 870-1-1IEC 870-1-2EN 60870-5-2