Rate-Adaptive Digital Subscriber Line: Difference between revisions

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{{About|the non-standardized DSL variant|the rate-adaptive mode of ADSL|ADSL#Operation|RE-ADSL2|ITU G.992.3 Annex L}}

'''Rate-adaptive digital subscriber line''' ('''RADSL''') is a pre-standard [[asymmetric digital subscriber line]] (ADSL) solution.<ref name="GoldenDedieu2004">{{cite book|author=Vladimir Oksman|editor1=Philip Golden|editor2=Hervé Dedieu|editor3=Krista S. Jacobsen|chapter=Fundamentals of Single-Carrier Modulation|title=Fundamentals of DSL Technology|chapterurl=https://books.google.com/books?id=m77kZl71gysC&pg=PA144|url=https://books.google.com/books?id=m77kZl71gysC|date=2 August 2004|publisher=CRC Press|isbn=978-0-203-31749-5|page=144}}</ref> RADSL was introduced as proprietary technology by AT&T Paradyne, later GlobeSpan Technologies Inc.,<ref name="globespan">{{cite web |title=GlobeSpan Emerges From the Former AT&T Paradyne as a Separate Technology Licensing Business |url=http://partners.nytimes.com/library/cyber/week/0604radsl.html |publisher=PR Newswire |date=1996-08-20 |accessdate=2014-03-06}}</ref> in June 1996.<ref name="ardsl-pr">{{cite web |url=http://partners.nytimes.com/library/cyber/week/0604radsl.html |title=AT&T Paradyne Announces High-Speed Modem Technology |date=1996-06-04 |accessdate=2014-03-06 |publisherwork=New York Times}}</ref> In September 1999, RADSL technology was formally described by [[American National Standards Institute|ANSI]] in T1.TR.59-1999.<ref name="ansi-store">{{cite web |url=http://webstore.ansi.org/RecordDetail.aspx?sku=T1.TR.59-1999 |title=T1.TR.59-1999 - Single-Carrier Rate Adaptive Digital Subscriber Line (RADSL)| date=September 1999| accessdate=2014-03-06 |publisher=ANSI}}</ref><ref name="tr59">{{cite web |url=http://www.csd.uoc.gr/~hy530/docs/RADSL.pdf |title=Technical Report No. 59 - Single-Carrier Rate Adaptive Digital Subscriber Line (RADSL) |date=September 1999 |accessdate=2014-03-06 |publisher=ANSI}}</ref> RADSL supports [[downstream (networking)|downstream]] data rates of up to approximately 8&nbsp;Mbit/s, [[upstream (networking)|upstream]] data rates up to approximately 1&nbsp;Mbit/s, and can coexist with [[plain old telephone system|POTS]] voice on the same line.<ref name="tr59"/>

RADSL allows rate-adaptation while the connection is in operation&nbsp;— rate-adaptation during connection setup is possible in many other DSL variants, including [[G.dmt]] and its successors. Rate-adaptation while the connection is in operation is specified as an option in [[ADSL2]], [[ADSL2+]], and [[VDSL2]], under the name ''seamless rate adaptation'' (SRA).<ref name="tr-197">{{cite web |url=http://www.broadband-forum.org/technical/download/TR-197.pdf |title=TR-197 - DQS: DSL Quality Management Techniques and Nomenclature |date=August 2012 |accessdate=2014-03-06 |publisher=Broadband Forum |page=29-3029–30}}</ref>

==Technology==

RADSL specifies two alternative modulation schemes, [[quadrature amplitude modulation]] (QAM) and [[carrierless amplitude phase modulation]] (CAP).<ref name="GoldenDedieu2004"/><ref name="tr59"/> RADSL is not interoperable with [[discrete multi-tone modulation|discrete multi-tone]] (DMT) modulation variants of ADSL, standardized in [[ANSI T1.413 Issue 2]] and [[G.dmt]] (G.992.1).<ref name="tr59"/> Upstream and downstream are [[frequency-division duplex]]ed, the upstream and downstream transmit PSD masks are identical to those in ANSI T1.413.<ref name="tr59"/>

In RADSL, the [[baud rate]], center frequency, and constellation size of the downstream and upstream channels can be adjusted while the connection is in operation.<ref name="tr59-pg104">{{cite webbook |chapter-url=http://www.csd.uoc.gr/~hy530/docs/RADSL.pdf|chapter=5.4.2.2.2 Link Initialization and Adaptation |page=104-105104–105 |title=Technical Report No. 59 - Single-Carrier Rate Adaptive Digital Subscriber Line (RADSL) |date=September 1999 |accessdate=2014-03-06 |publisher=ANSI}}</ref> Using this technique the line is more tolerant of errors caused by [[Noise (physics)|noise]] and signal loss. As the parameters are adjusted, the bandwidth may be markedly decreased if there is a large amount of line noise or signal degradation.

==See also==