ADSL
acronymISP & telecomnetworking
Asymmetric Digital Subscriber Line: broadband over the existing telephone pair by frequency division - voice below ~4 kHz, data above, a DSLAM terminating the data side at the exchange. Asymmetric because downstream gets most of the spectrum. Its arrival made home connections always-on.
The technology that let the same copper carry the internet full-time - the beginning of POTS's end.
ADSL carried broadband over ordinary telephone copper by using frequencies above the voice band, which is why a filter at each socket kept the two from interfering. Asymmetric described the split: much more capacity downstream than up, matching what browsing looked like at the time.
Its defining constraint was distance. Attenuation rises with line length, so the achievable rate fell off sharply with distance from the exchange, and two subscribers on the same package could receive very different service for reasons of geography alone. That single fact shaped a generation of complaints and is the reason cabinet-based deployments shortening the copper run mattered more than any protocol improvement.
Also known as: asymmetric digital subscriber line