automatic call back (Modem) (ACB)

Automatic Call Back (ACB) is a feature of telecommunications equipment for automatically interrupting an incoming connection and then setting up a connection in the opposite direction.

The Automatic Call Back feature is available for modems and routers. The called modem ensures that the connection is terminated and then re-establishes the connection to the calling modem on its own.

The ACB feature is a security function to prevent unauthorized connections; on the other hand, it serves to charge the first called connection with the costs of data transmission.