The 21st Century Network (21CN) programme is the network transformation project of the UK telecommunications company BT Group plc for data and voice. It had been intended to move BT's telephone network from the present 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.