BT’s vision for the future, the 21st Century Network (21CN), aims to empower the user by providing a simpler, single network for all services and providing an open interface for service providers to quickly and cleanly implement additional functions and services at the application layer.
21CN is comprised of a network based on the use of 3 primary nodes. With the addition of user premises (house, business, etc) and an intelligence layer called the iNode, the infrastructure can be thought of to comprise of the following 5 key elements.
Advertisement:
Premises
The premises component merely relates to the end user’s location. Whether it is a residential house, a small business or a corporate setting. Ideally, every premise’s will have some form of high-speed connection to 21CN, whether this is provided via copper Digital Subscriber Lines (DSL), or over a fibre optic link. The architecture of the consumer environment will give support to multiple IP sessions with both private and public IP addressing, Point to Point Protocol (PPP), Dynamic Host Configuration Protocol (DHCP), Network Address Translation (NAT) and both IPv4 and IPv6.
Provisions for the continued use of the traditional analogue Public Switched Telephone Network, or PSTN, will also be made.
Access Node
The access node, sometimes referred to as the MSAN domain (Multi Service Access Node), takes the various technologies supplied by the premises, such as voice, data and video services, and amalgamates them onto the IP-based 21CN. This includes converting any analogue voice into Voice over Internet Protocol (VoIP) by using the MSAN as what is known as a Media GateWay (MGW).
The Access Nodes will replace existing, traditional, systems, such as the PSTN, Integrated Services Digital Networks (ISDN) and Digital Subscriber Line Access Multiplexers (broadband DSLAMs) as used in current System X and AXE10 concentrators (RCUs).
MSANs come in two flavours:
Copper MSANs – which terminate the copper lines from the end user and
Fibre MSANs – which will terminate the fibre optic lines from larger sites, such as businesses.
The aim is for the Access Nodes to be implemented in about 5,500 BT exchanges and to convert all incoming data, whether digital or copper fed analogue, to the IP based network before running it to the Metro Node via fibre optics.
The MSAN will offer support for the legacy PSTN, VoIP, IP, Virtual Private Networks, ISDN and network layer 2 data services and will be provided in a number of sizes to provide the optimum solution for small, medium and large exchange scenarios.
Metro Node
The Metro Node acts as the gateway to the 21CN in much the same way as a common network router acts as the doorway to the Internet. Acting as the workhorse of the 21CN, the Metro Nodes take the data streams from the Access Nodes and convert them to their relevant IP-based services whilst encapsulating the IP traffic in Multi Protocol Label Switched (MPLS) tunnels for transmission over the Core Node. The Metro Node also provides IP traffic routing for the first time and access to the Internet and International Service Routing.
Session border controlling, Provider Edge (PE) IP routing and media servers & gateways will also be a core component of the Metro Nodes as well as the implementation of Quality of Service (QoS), Storage and Processing. Whilst call control will be instigated at the Metro Node level (via Softswitches or IP Multi-Media Subsystems (IMS)), this will be regarded as part of the encompassing iNode intelligence layer.
The Metro Nodes will also provide the mechanism for end users to interact with the 21st Century Network, allowing the creation and customisation of services, facilities and billing without the need for intervention by service providers.
Each Multi Service Access Node will be connected to at least two Metro Nodes in an effort to provide stability and alternate routing, thus reducing the effects of system downtime and technical failures. BT plans to incorporate approximately 100 Metro Nodes throughout the 21CN infrastructure, with the contractors named as Alcatel, Cisco and Siemens.
Core Node
The Core Nodes are simply high capacity, large scale, Multi Protocol Label Switching routers that provide a cost effective connection between the Metro Nodes using Dense Wave Division Multiplexing optical transport links. As the Internet Protocol traffic has been encapsulated in MPLS tunnels at the Metro Node, no customer IP traffic will be available at the Core Nodes. At this level, Internet Protocol will only be used to exchange routing information between the Core Nodes.
The Core Nodes will also provide Synchronous Digital Hierarchy (SDH) switching, enabling transmission speeds from 155mbit/s to 40Gbit/s using G.652 fibre cores.
Security is a particular concern throughout the Next Generation Network (NGN). At the Core Nodes BT aim to establish a system that is impenetrable to attacks from both the Internet and its internal customer base. The current solution is to allow no native IP traffic inside the Core Nodes apart from the control mechanism
There will be 10-20 Core Nodes established within the network with technology providers Cisco and Lucent supplying the MPLS routers.
iNode
Whilst not strictly a node in itself, the iNode acts as the 21CN’s intelligence layer. Encompassing the Access, Metro and Core Nodes, the iNode will implement a set of standard functions and common resources that will deliver layered services. Combinations of these capabilities will be used to offer different types of services.
The key purpose of the iNode is to provide a control mechanism for the other sections of the network, these responsibilities will include; authentication, session management, resource management, directories and location control.
The 21CN architecture specifies that the iNode layer will be based on the 3rd Generation Partnership Project (3GPP) Internet Protocol Multimedia Subsystem (IMS) – the same system currently being used by UK mobile communications operators and their subsequent 3G networks. However, in the case of the 21CN, BT plans to utilize the IMS in the iNode to control the fixed network. Aiming to modify the 3G IMS, in order to account for both wired and wireless connections, the compatibility of the network management can be future proofed.
There are currently plans to put into operation 10 iNodes across the UK, with the technology for voice service controllers, voice and application servers and signalling gateways, being provided by Ericsson.
It may be worth noting that the initial replacement for the legacy Public Switched Telephone Network (PSTN) will, more than likely, not be IMS compatible.