BT 21CN
The 21st Century Network (21CN) programme is the data and voice network transformation project, under way since 2004, of the UK telecommunications company BT Group plc. 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 by Openreach). Capital expenditure was put at £10 billion over five years, this being 75% of BT's total capital spending plans in that period. Architecture The new network is based on an architectural model of five classes of network nodes. These are: Premises Access (MSAN) Metro Core iNode Premises Premises nodes includes residential, small-medium enterprise (SME) and enterprise. The presumption is that all these will have high speed connections to the network, delivered over copper (in the form of ADSL