Multi-rate symmetric digital subscriber line

DSL technologies
	Standard
ADSL	ANSI T1.413 Issue 2 ITU G.992.1 (G.DMT) ITU G.992.2 (G.Lite)
ADSL2	ITU G.992.3 ITU G.992.3 Annex A ITU G.992.3 Annex B ITU G.992.3 Annex J ITU G.992.3 Annex L ITU G.992.3 Annex M ITU G.992.4
ADSL2+	ITU G.992.5 ITU G.992.5 Annex A ITU G.992.5 Annex B ITU G.992.5 Annex J ITU G.992.5 Annex M
HDSL	ITU G.991.1
HDSL2
IDSL
MSDSL
PDSL
RADSL
SDSL
SHDSL	ITU G.991.2
UDSL
VDSL	ITU G.993.1
VDSL2	ITU G.993.2

Multi-rate symmetric DSL (MSDSL) is a digital subscriber line technology with a maximum distance of 8,800 m (29,000 ft). It is capable of multiple transfer rates, as set by the Internet service provider, typically based on the service and/or price. The maximum speed in both directions is about 2 Mbit/s.

Technology

MSDSL is based on 2B1Q transmission with a capacity of 2.32 Mbit/s. The bandwidth is split between a full E-carrier E1 payload (2.048 Mbit/s), with the remaining bandwidth accommodating up to three voice channels or two ISDN channels. Additional bandwidth is used for management purposes. Transmission over the single pair requires echo cancellation and adaptive equalizers in order to achieve the maximum range at a specific rate. For each user rate, the modem changes the 2B1Q transmission rate, employing different filters and equalizer settings. The modem's adaptive setting is determined during its initial use, and continues constantly during operation.