ADSL modems can be purchased with various speed range and capabilities. Downstream data rates depend on number of factors, including the length of the copper line, it s wire gauge, presence of bridged tapes and cross-coupled interference. Line attenuation increases with line length and frequency, and decreases as wire diameter increases. Km Premises beyond these distances can be reached with fiber based digital loop carrier systems.
Many applications envisioned for ADSL involve digital compressed video.
As a real time signal, digital video can t use link or network level error control procedures commonly found in data communication systems.