Rate-Adaptive Digital Subscriber Line
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 edit
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 edit
- Etherloop—another DSL variant using single-carrier modulation (QAM)[1]
- High-bit-rate digital subscriber line (HDSL)—another DSL variant using single-carrier modulation (CAP)[1]
- Multi-rate symmetric digital subscriber line (MSDSL)—another DSL variant using single-carrier modulation (CAP)[1]
- Very-high-bit-rate digital subscriber line (VDSL)—another DSL variant using single-carrier modulation (QAM)[1]
References edit
- ^ a b c d e f Vladimir Oksman (2 August 2004). "Fundamentals of Single-Carrier Modulation". In Philip Golden; Hervé Dedieu; Krista S. Jacobsen (eds.). Fundamentals of DSL Technology. CRC Press. p. 144. ISBN 978-0-203-31749-5.
- ^ "GlobeSpan Emerges From the Former AT&T Paradyne as a Separate Technology Licensing Business". PR Newswire. 1996-08-20. Retrieved 2014-03-06.
- ^ "AT&T Paradyne Announces High-Speed Modem Technology". New York Times. 1996-06-04. Retrieved 2014-03-06.
- ^ "T1.TR.59-1999 - Single-Carrier Rate Adaptive Digital Subscriber Line (RADSL)". ANSI. September 1999. Retrieved 2014-03-06.
- ^ a b c d e "Technical Report No. 59 - Single-Carrier Rate Adaptive Digital Subscriber Line (RADSL)" (PDF). ANSI. September 1999. Retrieved 2014-03-06.
- ^ "TR-197 - DQS: DSL Quality Management Techniques and Nomenclature" (PDF). Broadband Forum. August 2012. p. 29–30. Retrieved 2014-03-06.
- ^ "5.4.2.2.2 Link Initialization and Adaptation" (PDF). Technical Report No. 59 - Single-Carrier Rate Adaptive Digital Subscriber Line (RADSL). ANSI. September 1999. p. 104–105. Retrieved 2014-03-06.