Editing Data access arrangement

{{Short description|Concept in circuitry networks}}
[[File:Fritz!Box Fon WLAN 7270 - IXYS Litelink CPC5621A-3340.jpg|thumb|Phone Line Interface IC [[IXYS Corporation|IXYS]] Litelink CPC5621A]]
The term '''data access arrangement''' (DAA) has the following meanings: 
#In [[public switched telephone network]]s, a single item or group of items at the customer side of the [[network interface device]] for [[data transmission]] purposes, including all equipment that may affect the characteristics of the interface. 
#A data [[Telecommunication circuit|circuit]]-terminating equipment ([[Data circuit-terminating equipment|DCE]]) supplied or approved by a [[common carrier]] that permits a DCE or data [[terminal equipment]] ([[Data terminal equipment|DTE]]) to be attached to the common carrier network.

[[Data access]] arrangements are an integral part of all [[modem]]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]] - to ensure the network was protected. These devices were not required for Bell-provided equipment, only equipment made by independent manufacturers.<ref name=":0">{{Cite web|date=1972-01-09|title=Computerworld|url=https://archive.org/details/computerworld6197unse2|access-date=2020-08-13|website=Internet Archive|language=en}}</ref><ref name=":1">{{Cite book|last=Enterprise|first=I. D. G.|url=https://books.google.com/books?id=2otFgtEgfiEC&dq=FCC+%22automatic+DAA%22&pg=PA1|title=Computerworld|date=1975-11-12|publisher=IDG Enterprise|language=en}}</ref>

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,<ref>{{Cite web|date=1972-07-19|title=Computerworld|url=https://archive.org/details/computerworld6197unse28|access-date=2020-08-13|website=Internet Archive|language=en}}</ref> and the FCC began investigations into the legality of the practice.<ref name=":0" /> 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.<ref name="Computerworld">{{Cite web|date=1969-09-24|title=Computerworld|url=https://archive.org/details/computerworld3265unse13|access-date=2020-08-13|website=Internet Archive|language=en}}</ref>

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.<ref name="Computerworld"/>

In 1975, the FCC implemented [[Title 47 CFR Part 68|Part 68]] of the FCC Rules,<ref>{{Cite book|url=https://docs.fcc.gov/public/attachments/FCC-00-400A1.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://docs.fcc.gov/public/attachments/FCC-00-400A1.pdf |archive-date=2022-10-09 |url-status=live|title=2000 Biennial Regulatory Review of Part 68 of the Commission's Rules and Regulations|publisher=FCC|pages=51|quote="[...]in 1975 when the Part 68 program was originally implemented"}}</ref> 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,<ref name=":1" /> 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.<ref>{{Cite book|last=Enterprise|first=I. D. G.|url=https://books.google.com/books?id=AGFRu5N2hloC&dq=computerworld%20modem&pg=PA102|title=Computerworld|date=1977-06-13|publisher=IDG Enterprise|language=en}}</ref>

==References==
{{Reflist}}
*{{FS1037C}}

==External links==
* [https://web.archive.org/web/20060309114314/http://www.3amsystems.com/wireline/daa.htm Wireline DAA] - introductory slides by 3am Systems
* [http://www.scantec.de/Whitepaper/TDK/embedded-modem-designs.pdf Direct-Access Arrangements Are Crucial To Successful Embedded-Modem Designs] - in-depth article by Jeff Sorensen

[[Category:Local loop]]