BT 21CN

The 21st Century Network (21CN) programme is the network transformation project of the UK telecommunications company BT Group plc for data and voice. It was intended to move BT's telephone network from the AXE/System X Public Switched Telephone Network (PSTN) to an Internet Protocol (IP) system. As well as switching over the PSTN, BT planned to deliver many additional services over their new data network, such as on-demand interactive TV services.

BT originally stated that it would accrue annual savings of £1 billion when the transition to the new network was completed, and hoped to have over 50% of its customers transferred by 2008 (see External links below for current progress on the roll-out of optical fibre.) Capital expenditure was put at £10 billion over five years, this being 75% of BT's total capital spending plans in that period.

21CN has been heavily delayed and is yet to roll out in many parts of the United Kingdom, where the legacy circuit-switched network is still in place.