A Data Access Arrangement (DAA) is an electronic interface within a computer and its modem to a public telephone line. A DAA is also sometimes called a Telephone Line Interface Circuit (or Module). DAAs are required in any device that attaches to the public switched telephone network ( PSTN ), including fax machines, private branch exchange , set-top box , and alarm systems. Among other things, the DAA isolates the electronic device from the higher voltage on the telephone line. DAA circuitry requires registration with the telephone system governing authority (such as the Federal Communications Commission in the U. S.). However, most manufacturers of modems and other devices build an already-approved DAA design into the modem.
A Data Access Arrangment can be built into a computer's motherboard but is more commonly built into the modem.