BT's new Asymmetric Digital Subscriber Line technology (ADSL) allows high-speed data to be carried on existing copper telephone lines at the same time as normal voice calls, so that broadband internet users will no longer need to have fibre-optic cable fitted. Standard modems carry 56 kilobytes of data per second but ADSL carries 500. So far, up to 1,000 of BT's 6,500 local exchanges have been fitted with the fibre-optic connections which deliver the data to the copper-wire business or household networks.