Multi-rate symmetric digital subscriber line

Content sourced from Wikipedia, licensed under CC BY-SA 3.0.

Multi-rate symmetric DSL (MSDSL or MDSL) is a proprietary, non-standard symmetric broadband technology that runs over a single copper pair. It can reach up to 29,000 feet (8,800 meters) from the phone office. It supports multiple fixed data rates chosen by the service provider, usually based on the service plan or price. There are eight speeds, ranging from 160 kbit/s to 2.32 Mbit/s. MSDSL uses either 2B1Q or carrierless amplitude phase (CAP) modulation to reach up to 2.32 Mbit/s.

The line’s bandwidth is typically shared: a full E-carrier E1 payload of 2.048 Mbit/s is carried, with the remaining bandwidth available for up to three voice channels or two ISDN channels. Extra bandwidth is reserved for management and control.

Because MSDSL uses a single pair, it requires echo cancellation and adaptive equalizers to achieve the maximum range at a given rate. For each service rate, the modem adjusts the transmission rate and uses different filters and equalizer settings. The modem determines its adaptive settings at first use and keeps them during operation, adapting if the rate changes.