The term data access arrangement (DAA) has the following meanings:
#In
public switched telephone network
The public switched telephone network (PSTN) is the aggregate of the world's telephone networks that are operated by national, regional, or local telephony operators. It provides infrastructure and services for public telephony. The PSTN consists o ...
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 '':de:Abschlusspunkt Linientechnik, Abschlusspunkt LinienTechnik'' (APL, "Demarcation point")
In telecommunications, a ...
for
data transmission
Data communication, including data transmission and data reception, is the transfer of data, signal transmission, transmitted and received over a Point-to-point (telecommunications), point-to-point or point-to-multipoint communication chann ...
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 (legal system), civil law systems,Encyclopædia Britannica CD 2000 "Civil-law public carrier" from "carriage of goods" usually called simply a ''carrier ...
that permits a DCE or data
terminal equipment
In telecommunications, 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.
* ...
(
DTE) to be attached to the common carrier network.
Data access
Data access is a generic term referring to a process which has both an IT-specific meaning and other connotations involving access rights in a broader legal and/or political sense. In the former it typically refers to software and activities relat ...
arrangements are an integral part of all
modem
The Democratic Movement (, ; MoDem ) is a centre to centre-right political party in France, whose main ideological trends are liberalism and Christian democracy, and that is characterised by a strong pro-Europeanist stance. MoDem was establis ...
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
The Carterfone is a device invented by Thomas Carter. It connects a two-way radio system to the telephone system, allowing someone on the radio to talk to someone on the phone. This makes it a direct predecessor to today's autopatch. The conne ...
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
Western Electric Co., Inc. was an American electrical engineering and manufacturing company that operated from 1869 to 1996. A subsidiary of the AT&T Corporation for most of its lifespan, Western Electric was the primary manufacturer, supplier, ...
- 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 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