A Digital Subscriber Line DSL variant with E1-like data rates (72 to 2320 kbit/s).
It runs over one pair of copper wires, with a maximum range of about 3 kilometers. The main difference between ADSL and SDSL is that SDSL has the same upstream data transfer rate as downstream (symmetrical), whereas “ADSL”/a/adsl always has smaller upstream bandwidth (asymmetrical).
However, unlike ADSL, it can’t co-exist with a conventional voice service on the same pair as it takes over the entire bandwidth.
It is quite expensive and is mainly targetted at small and medium businesses who may host a server on site (eg a Terminal Server) so don’t want to use ADSL, but don’t need the higher performance of a leased line.
SDSL was never properly standardised until Recommendation G.991.2 (ex-G.shdsl) was approved by ITU-T.
SDSL is often confused with G.SHDSL and unfortunately, in Europe G.SHDSL was standardized by ETSI using the name ‘SDSL’.
This ETSI variant is compatible with the ITU-T G.SHDSL standardized regional variant for Europe.
Equipment routing SDSL support is usually proprietary equipment which only speaks to
SDSL equipment from the same vendor, or to SDSL equipment from other vendors that use the same DSL chipset.
Most new installations use G.SHDSL equipment instead of SDSL.