BT’s 21CN (21st Century Network) or BT NGN project is a unique example of migration from a traditional network to all IP NGN using NGN/IMS architecture. The project plans to migrate all of BT’s 30 million fixed copper lines to a NGN-enabled network by 2012.
The main motivation of BT’s 21CN is to reduce cost by
migrating from the currently 16 independent network
platforms to a single network which supports end-to-end
IP-based network. BT plans to realize annual operational
expenditure savings of around USD 2 billion after the migration.
There are five strategic domains in 21CN network:
1. Access domain refers to the edge of 21CN that links to BT’s existing access network. Multiservice access nodes (MSANs) aggregate the voice, data and video services from end users onto the 21CN core IP-based network. They replace the service-specific equipment of the legacy network. (Approximately 5,500 BT sites in the United Kingdom will house either copper MSANs or fibre MSANs).
2. Metro node refers to nodes that provide the IP routing,Ethernet switching, SDH switching and gateways to existing networks for the unified 21CN. There will be approximately 100 metro nodes in the United Kingdom.
3. Core node refers to high-capacity, large-scale routers that provide cost-efficient connectivity between metro nodes.There will be approximately 20 core nodes in the United Kingdom.
4. i-Node 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 country.
5. Transmission includes the fibre transport infrastructure that connects all nodes in the 21CN, as well as the electronics that convert the signals carried at high capacity over the cables that connect the MSANs and the metro and core nodes. New fibres of 2,300km are added in the network.
It is important to note that 21CN is not associated per se to an access overhaul. Even though broadband access is mentioned as the basic access mode and IMS multimedia architecture will be used, 21CN’s objective is grounded on network core migration, with its associated cost reductions. However, BT has not exclude the upgrading of their access network with fibre and BWA.
Besides the challenging task of migrating 30 million users
in 5 years, 21CN involves a number of major technical challenges:
• Making eight equipment manufacturers share compatible
network elements and a common goal.
• Making immature technologies work together (e.g.,
21CN’s IMS needs further development with regard to
the integration of BT’s Fusion service, which converges
fixed and mobile services, and BT’s Communicator,
which is a VoIP consumer service).
Source: ITU
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