Data Access Arrangement

What Does Data Access Arrangement Mean?

Data access arrangement (DAA) is a computer modem with a built-in electronic system that interfaces with public switched telephone networks (PSTN). DAA is required for PSTN devices, including set-top boxes, fax machines, private branch exchanges (PBX) and alarm systems.


DAA devices are isolated from high voltage phone lines, but system authorities require device registration. Preregistered DAA is built into most modems and devices.

DAA is also known as a telephone line interface circuit.

Techopedia Explains Data Access Arrangement

There are three international DAA standards:

  • North America: Federal Communications Commission (FCC) Part 68, which parallels many Canadian and Mexican regulations
  • Europe: European Telecommunications Standards Institute (ETSI) Common Technical Regulation (CTR) 21
  • Japan: Japan Approvals Institute for Telecommunications Equipment (JATE)

A key DAA design factor is layout, which defines the area between line and modem components. Examples include:

  • Optocoupler: Computer and phone line are connected without surge risk or damage
  • Clare Based: Uses two high-voltage isolation capacitors to implement caller ID and ring detection with separate PSTN/pathways
  • Capacitive-Coupled: Uses integral modem system components to directly interface with the digital signal processor (DSP)
  • Simple: Includes incoming ring detector and hook switch relays and provides other application-specific functions

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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.