ADSL (Asymmetric Digital Subscriber Line) provided high-speed internet over existing copper telephone lines. "Asymmetric" means the download and upload speeds differ. On NTT East's Flets ADSL, the fastest tier (Moa III, 47M type) offered 47Mbps down and 5Mbps up, weighting the available bandwidth heavily toward downloads. All tiers were best-effort, and the figures were theoretical maximums.
Commercial ADSL service began in Japan around 2000. Yahoo! BB, launched in September 2001, and rival entrants triggered a price war that drove explosive adoption. Orders of magnitude faster than 56kbps dial-up, ADSL brought the idea of an "always-on" connection into ordinary homes and sharply accelerated Japan's shift to broadband.
ADSL's weakness was that speeds fell as the distance from the telephone exchange grew. NTT East itself noted that line length, facility conditions, interference from other lines and equipment inside the customer's home could all reduce speeds or make the service unusable. Because it ran over the same copper as telephone service, quality was easily swayed by those conditions.
As fiber optic lines spread, ADSL subscriptions declined steadily. Flets ADSL was withdrawn in stages, starting with areas where fiber was already available: NTT East ended it on 31 January 2025 and NTT West on 31 January 2026, with both companies closing new and relocation orders on 31 July 2023. Roughly 25 years after its commercial debut around 2000, the service was gone, but its role in spreading internet access in Japan was immense. See telephone evolution for the technology timeline.