An ITU standard (1968) for automatic calling and/or answering equipment on dial-up lines. V.25 bis had three modes: asynchronous (rarely used), character-oriented synchronous (bisync) and bit-oriented synchronous (HDLC/SDLC). Both synchronous versions were used in IBM AS/400 and other small-to-medium sized computers that did automatic dialing for remote job entry.
Due to the popularity of the Hayes AT Command Set, V.25bis was not used as widely in North America. It did not perform modem configuration functions and was limited to dialing and answering calls. See
AT command set.