 it must be capable of isochronous packet re-assembly. It must have security built in, far more than the current Internet technology, especially for protection of VoIP. The foundation is IPv6. Such networks are often being constructed as a federator for other networks. One major application here is the transport of backhaul mobile traffic, from other operators but also for expansion of the broadband local loop, be it by forms of xDSL, or the broadband wireless access technologies being proposed in Korea and now in the United States (by Nextel) for Internet access. One prime example for detailed examination is BT's IP network architecture with its 21st Century Network Project (21CN). 21CN is a complete IP infrastructure, being rolled out to 2008. It is based upon multi-protocol label switching (MPLS), that carries voice, data and Internet services over the one network, rather than today's multitude of networks offering specific services. BT sees that services like ATM, TDM, frame relay etc., beyond the access network layer, can be collapsed into a far simpler structure - a core - based upon existing MPLS and DWDM (dense wavelength division multiplexing) technologies. MPLS offers high-performance packet switching along predetermined paths and also uses unique route distinguishers. A vastly simplified core reduces the number of copper pairs and fibre in the system. It means fewer network elements and simpler network management. It also reduces the number of service management organisations, equipment in outside plant and buildings. It will reduce the number of different technologies in the network, and so reduce operating costs. In the 21CN, BT has combined MPLS technology with traffic engineering techniques that differentiate between time-critical, high-priority traffic, and delay-tolerant, low-priority traffic. 21CN should reduce the complexity of BT's infrastructure with claimed elimination of 100 000 network components by establishing a single platform that is multi- service and future proof, on IPv6. INFRASTRUC