AT command
The AT command set is a Hayes command set developed by the Hayes company for modem control from terminal programs.
This command set always starts with the command AT for Attention, hence the name, and has developed as a quasi- standard.
The AT command set contains, among others, commands for dialing into a telephone network, for redialing, number dialing, transmission format, speaker control, port control and assignment, connection time, control procedures, and for transmit and receive mode.