During the design stage, BT consulted widely with its customers and with the world's leading telecoms and IT suppliers. BT will continue this partnership approach in order to choose the best of breed technology platforms available worldwide and to minimise any implementation risk by choosing proven technology platforms for each element of the overall programme.
There are five 21CN strategic domains, namely:
Access domain - the edge of 21CN linking to BT's existing access network. Multi-service access nodes (MSANs) aggregate the voice, data and video services from end users on to the 21CN core IP-based network. They replace the service-specific equipments of the legacy network - for example System X and AXE10 concentrators for PSTN and ISDN and DSLAMs for broadband. Approximately 5,500 BT sites in the UK will house MSANs with Fujitsu and Huawei selected as suppliers.
There are two types of MSANs:
Copper MSANs - which terminate the copper cables from end user customers
Fibre MSANs - which terminate the fibre cables from many business sites.
Metro node - provides the IP routing, Ethernet switching, SDH switching and gateways to existing networks for the unified 21CN network for voice, data and video. There will be approximately 100 metro nodes in the UK with Alcatel, Cisco and Siemens selected to provide the technology which includes Provider edge IP routers; Ethernet switches; media servers; trunk media gateways and session border controllers.
Core node - the high capacity, large scale routers providing cost efficient connectivity between metro nodes. There will be approximately 20 core nodes in the UK with Cisco and Lucent selected to provide the technology, MPLS routers.
i-Node - this is where the service execution functionality is located - in essence the intelligence that controls services. It includes soft switches, network intelligence and bandwidth management capabilities. There will be approximately 10 i-Nodes in the UK with Ericsson selected to provide the technology for the control of voice services which includes call servers; application servers and signalling gateways.
Transmission - this includes the optical fibre transport infrastructure that connects all nodes in 21CN but also the electronics that convert the signals carried at high capacity over the cables connecting the MSANs, metro and core nodes. Much of the optical fibre infrastructure is already in place and Ciena and Huawei have been selected to provide the electronics which include WDM and high bit-rate SDH cross connects.