Rate-Adaptive Digital Subscriber Line

Rate-adaptive digital subscriber line (RADSL) is a pre-standard asymmetric digital subscriber line (ADSL) solution.<ref name="GoldenDedieu2004">Template:Cite book</ref> RADSL was introduced as proprietary technology by AT&T Paradyne, later GlobeSpan Technologies Inc.,<ref name="globespan">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> in June 1996.<ref name="ardsl-pr">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In September 1999, RADSL technology was formally described by ANSI in T1.TR.59-1999.<ref name="ansi-store">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="tr59">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> RADSL supports downstream data rates of up to approximately 8 Mbit/s, upstream data rates up to approximately 1 Mbit/s, and can coexist with POTS voice on the same line.<ref name="tr59"/>

RADSL allows rate-adaptation while the connection is in operation — 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">{{#invoke:citation/CS1|citation |CitationClass=web }}</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 (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 duplexed, 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">Template:Cite book</ref> Using this technique the line is more tolerant of errors caused by 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

• Etherloop—another DSL variant using single-carrier modulation (QAM)<ref name="GoldenDedieu2004"/>
• High-bit-rate digital subscriber line (HDSL)—another DSL variant using single-carrier modulation (CAP)<ref name="GoldenDedieu2004"/>
• Multi-rate symmetric digital subscriber line (MSDSL)—another DSL variant using single-carrier modulation (CAP)<ref name="GoldenDedieu2004"/>
• Very-high-bit-rate digital subscriber line (VDSL)—another DSL variant using single-carrier modulation (QAM)<ref name="GoldenDedieu2004"/>