Rate-Adaptive Digital Subscriber Line

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This article is about the non-standardized DSL variant. For the rate-adaptive mode of ADSL, see ADSL § Operation. For RE-ADSL2, see ITU G.992.3 Annex L.

Rate-adaptive digital subscriber line (RADSL) is a pre-standard asymmetric digital subscriber line (ADSL) solution.[1] RADSL was introduced as proprietary technology by AT&T Paradyne, later GlobeSpan Technologies Inc.,[2] in June 1996.[3] In September 1999, RADSL technology was formally described by ANSI in T1.TR.59-1999.[4][5] 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.[5]

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).[6]

Technology

RADSL specifies two alternative modulation schemes, quadrature amplitude modulation (QAM) and carrierless amplitude phase modulation (CAP).[1][5] 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).[5] Upstream and downstream are frequency-division duplexed, the upstream and downstream transmit PSD masks are identical to those in ANSI T1.413.[5]

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.[7] 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

References

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