Fritz!Box Fon WLAN 7270 - IXYS Litelink CPC5621A-3340

The term data access arrangement (DAA) has the following meanings: #In

public switched telephone network The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telep ...

s, a single item or group of items at the customer side of the

network interface device upTwo simple NIDs, carrying six lines each, on the outside of a building upA German copper phone line termination box called '' Abschlusspunkt LinienTechnik'' (APL, " Demarcation point") In telecommunications, a network interface device (NID; ...

for

data transmission Data transmission and data reception or, more broadly, data communication or digital communications is the transfer and reception of data in the form of a digital bitstream or a digitized analog signal transmitted over a point-to-point or ...

purposes, including all equipment that may affect the characteristics of the interface. #A data circuit-terminating equipment ( DCE) supplied or approved by a

common carrier A common carrier in common law countries (corresponding to a public carrier in some civil law systems,Encyclopædia Britannica CD 2000 "Civil-law public carrier" from "carriage of goods" usually called simply a ''carrier'') is a person or compan ...

that permits a DCE or data

terminal equipment In telecommunication, the term terminal equipment has the following meanings: * Communications equipment at either end of a communications link, used to permit the stations involved to accomplish the mission for which the link was established. * I ...

( DTE) to be attached to the common carrier network. Data access arrangements are an integral part of all

modem A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by modulating one or more c ...

s built for the public telephone network. In view of mixed voice and data access, DAAs are more generally referred to as direct access arrangements.

Requirement for DAAs

While DAA now describes an integral component of a device that connects to the telephone network, during the 60s and 70s it described a separate device mandated by the Bell System, connected between the telephone line and non-Bell equipment, typically a modem. Following the Carterfone decision, which required Bell to allow customers to attach any non-harmful equipment to their network, Bell mandated that subscribers use PCAs/DAAs - purchased exclusively from

Western Electric The Western Electric Company was an American electrical engineering and manufacturing company officially founded in 1869. A wholly owned subsidiary of American Telephone & Telegraph for most of its lifespan, it served as the primary equipment ma ...

- to ensure the network was protected. These devices were not required for Bell-provided equipment, only equipment made by independent manufacturers. At the time, some subscribers believed that the DAA was a scheme by AT&T to penalize and discourage use of non-Bell modems and recover lost profits from hardware sales, and the FCC began investigations into the legality of the practice. Subscribers also became frustrated when Bell failed to deliver DAAs in a timely fashion after the ruling, leading to the use of unauthorized third-party DAAs. There were two main varieties of DAA described by AT&T: manual and automatic. A manual DAA required a call to be initiated (or answered) as normal, at which point it could then be connected to the third-party device, while an automatic DAA allowed an attached device to be connected without human intervention, important for receiving modem use. In 1975, the FCC implemented

Part 68 'Title 47 CFR Part 68'' is a section of the Code of Federal Regulations of the United States that regulate the direct electrical connection of telecommunications equipment and customer premises wiring with the public switched telephone network, cer ...

of the FCC Rules, which granted permission for direct connection of any equipment to the telephone network given compliance with specific electrical requirements. This technically eliminated the need for DAAs, although the first modem that didn't require a separate DAA was not marketed until 1977 when a court ruled that Part 68 was legal.

References

*{{FS1037C

External links

Wireline DAA
- introductory slides by 3am Systems
Direct-Access Arrangements Are Crucial To Successful Embedded-Modem Designs
- in-depth article by Jeff Sorensen Local loop