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Service providers will need to have a look at the example of how 21Century network of British Telecom is creating waves by trying to transform its legacy network into a single multi service network. From a network technology perspective, BT's 21CN programme is transforming many legacy networks into a simpler, but more powerful, multi-service network, which will be the platform for a full portfolio of new wave services, as well as continuing to support traditional services. There is a lot of interest in next generation networks, but how are they different to legacy networks and why is the architecture considered to be truly disruptive?   

In the traditional world, services, such as voice require their own discrete networks with discrete infrastructure, systems, management and services to support them. In an IP world, services are applications. For example, voice becomes one of many applications running on a common platform and the systems, services and management processes are shared. In essence, the transport layer-the electronics that convert communications signals and convey the communications to its destination-is separated from the session control or signaling. This separation leads to 'open architecture' that challenges traditional business models.  With open architectures, it is possible for thousands of applications providers to 'experiment' with new attractive applications that can be launched quickly and relatively cheaply. No longer are these things the sole province of the telco. 

21CN is BT's next generation network which it is building in the UK and markets which BT servers. It is an advanced broadband network based on intelligent systems, Internet Protocol (IP), Session Initiation Protocol (SIP) and Multi-Protocol Label Switching (MPLS). IP is key to 21CN because it has the potential to act as a common transport protocol for all types of communication and applications; SIP allows the service provider to control the communications activity to meet a customer's requirements and MPLS enables the efficient designation and routing of IP traffic flows.

The shape or topology of 21CN is being fashioned by economic analysis that takes into account advances in fiber optic transmission. It results in network designs that have fewer main switching/routing nodes and, as a rule of thumb, longer transmission links between nodes. The physical simplicity and the reduction in the number of operating facilities will have the added benefit of enhancing reliability.

Drivers for 21CN
Radical improvements for the customers are the promised results of BT's drive to build a 21st century network (21CN). This initiative is primarily aimed at developing a truly customer-focused network, to be operated at best cost, that will ultimately allow communications in a range of formats across an IP based network. It is a massive task, and illustrates BTs determination to be forward looking, both for the sake of its wholesale and retail customers and the market, financial and technological needs. The new network will be aimed at providing flexibility, including mobility, and personalization, so that customer communications are seamless, offer multi-device capability and secure communications.  The 21CN programme has three key objectives-to transform the customer experience; to increase speed to market and; to become a cost leader.

How Different Will Be 21Century Network
Over the years, BT has provided a series of separate products and services created by disparate technologies-many of them excellent in their own right. But they haven't been integrated with each other, and they've all had their own separate systems and service management. They simply do not have the same look and feel to the customer. Hence, BT is transforming the many legacy networks into a simpler, but more powerful, single, network, which will be the platform for a full portfolio of new wave services, as well as continuing to support the more traditional services. The new network will have far fewer components-nearly 50% in many areas-in terms of, for example, switches, hubs and routers. The shape or topology of the network will be fashioned by advances in fiber optic technology. It will be consolidated to a fewer number of operating facilities which will enhance reliability at the same time.

Time Taken To Build The Network
Having already undertaken a considerable amount of research and design work, BT on June 9, 2004 set out the timetable for the transformation of its UK networks. It announced a five-year programme to underpin the next generation of converged, multimedia communications services. The early stages include the initial migration of PSTN to an IP network and a deep fiber trial.

Cost In Building 21CN
BTs 21CN programme will be funded from the previously announced CAPEX envelope of Ł3 bn per annum. From this year, about two-thirds of the annual spend is directed to 21CN and other new and intermediate technologies and this proportion is expected to increase. However, the programme is also addressing the need to cut operational costs and to position the company to offer a host of new services for customers.

Latency Specifications For 21CN
BT is seeking to minimize the latency of information within BT's network. Services, which are latency-critical, will continue to be provided on an SDH TDM infrastructure, where latency will be minimal. Other services will be emulated over an MPLS core network, and will experience an additional packetization delay, of the order of 5ms. Voice services will be carried as VoIP, where BT is targeting a delay of less than 35ms end to end for the segment of the call carried on BT's network, assuming a single TDM;IP conversion at each end. In addition, there will be a speed of light delay due to distance, being at worst 8ms for calls within the UK. The eight strategic suppliers chosen to work with BT are Alcatel, Ciena, Cisco, Ericsson, Fujitsu, Huawei, Lucent and Siemens.

Products And Services
21CN will allow future products and services to be built using common, reusable capabilities, designed to create a world-class experience for customers while at the same time reducing costs and bringing products to market more quickly. BT has drawn up a set of common capabilities. These are building blocks that can be combined in different ways to create new services, something like chemical elements, which combine to form different compounds. Re-using proven components in this way can save time, reduce costs and increase consistency for customers, as well as meaning that new services can be brought to customers faster than before.

Examples Of These Capabilities
Authentication: The ability to identify an individual or device based on a range of credentials such as a username, password or even biometric data such as fingerprints and eye retinas.
Content: Turning content such as books, audio tapes or videos into digital content that can be used online.
Application Driven QoS: The ability of the network to configure itself to deliver the services a customer requires in real time, such as flexing bandwidth when sending a video file.

Technologies Behind 21CN
Ethernet: Ethernet's ubiquity, simplicity and low costs make it attractive for the links between the nodes in BT's 21CN. As a first step, the backhaul links between the MSANs and the metro nodes will be Ethernet-based. Arguably Ethernet today does not have all the characteristics to make it a general purpose link layer protocol. Currently BT is working with equipment suppliers and standards bodies to ensure it is. BT believes that truly carrier class Ethernet needs to be able to offer the same level of security and resilience, and the same end-to-end fault and performance monitoring, simple and quick error location and remote configuration, as traditional telecom technologies offer. In 21CN, Ethernet has to be able to offer these characteristics across multi-vendor environments. When BT completes the development of 21CN, it will represent one of the largest installations of Ethernet in any carrier's network, anywhere in the world.
IP Multi-media Subsystem-IMS: The IMS was originally designed for the mobile industry to add a common session layer on top of the IP network layer to support many different applications. The applications can range from real-time call control applications to multi-media streaming applications for content services.
    The IMS was standardized for the mobile industry by an organization called 3GPP (3G Partners Program). Recently, the standard has been augmented for fixed networks by ETSI TISPAN, adding authentication, authorization and accounting (AAA) and quality of service (QoS) control for fixed access networks.
Multi-Protocol Label Switching -MPLS: With BT's 21CN, communications are sent over a high quality, secure network using IP as the transport protocol. To maximize efficiency, a technique called MPLS allows different services, for example voice, audio and video calls, to be assigned their own portion of the capacity on the links between metro nodes and for that portion to be given the appropriate prioritization. This is an essential protocol for converged IP networks since it ensures, for example, that voice is prioritized over less time-critical data.   
Synchronous Digital Hierarchy -SDH: SDH will continue to be used as part of 21CN. SDH will provide transmission pipes that run between the network nodes. Those pipes are typically at transmission speeds of 2.5Gbit/s or 10Gbit/s although lower speeds of 155Mbit/s and 622Mbit/s are also used.
Session Initiation Protocol-SIP: SIP is a 'signalling' standard for setting up a session across an IP network.
Virtual Local Area Network - VLAN: 21CN VLANs allow us to partition the capacity of the links according to the needs of the different types of service, for example voice and video.
Wave Division Multiplexing - WDM: WDM is a multiplexing technology used for fiber. It acts like a prism, separating the light in the fiber into different colored beams, or different wavelength channels, each of which carries as much data as a single fiber, which has not had WDM applied to it.

(Source: British Telecom)