urces is impressive according to Figure 11.12. In a way it is easier to say what is not included, such as service enablers, application logic. Packet Backbone 12.1 OBJECTIVES The packet backbone is the main solution regarding core connectivity. Figure 12.1 shows its central network position. What are the technical and business requirements on the packet backbone? What protocol stack is available to fulfil the requirements, especially the IP and ATM enablers? What about control and management? The main requirements on the backbone are low cost, high capacity, high quality and reliability. The fulfilment of these needs is feasible: Low cost: low cost per circuit because of low fibre cost and very high capacity in a fibre. High capacity: with new techniques, such as dense wavelength division multiplex (DWDM), 10 million users can communicate simultaneously over a fibre optic cable with 10 Mbit/s (!) bandwidth per user. High quality: normally fibre based with very few bit errors. However, the combination of real-time services and packet switching is still a challenge, requiring a set of QoS enablers and fairly sophisticated traffic engineering especially for IP transfer of traffic with multiple QoS requirements. Terminal if any Service network, if any Content Content Applications Service enablers Network control and intelligence Access Core connectivity Figure 12.1 Position of the packet backbone Understanding Changing Telecommunications - Building a Successful Telecom Business. Edited by A. Olsson © 2004 John Wiley & Sons, Ltd ISBN: 0-470-86851-1 Understanding Changing Telecommunications - Building a Successful Telecom Business Reliability: redundant capacity in ring/meshed networks, protection logic and cross- connect equipment for fast rearrangement in case of cable breaks etc. See also the CD IP Internetworking, especially Chapters 11 and 12. The main objective of this chapter is therefore to gain further knowledge about provid- ing a bit-transporting backbone that fully responds to the demands of the service pla