ny parts of Chapter 8. As mentioned above, the crucial services are real-time services, traditionally voice but also in the future video telephony and similar multimedia real-time services. As usual QoS and security are in focus. The heritage from the previous century is a number of vertical networks, which often carry the same media traffic, and therefore need interconnection. See Figure 12.3. In this chapter the design of a universal backbone is in focus. Thus, instead of designing many vertical networks, including their respective backbone, let us look at a common multi-service backbone serving the 'all-access architecture'. Figure 12.4 also shows its role as a bridge to and between other network types. Thus, let us disregard the fact that many access network operators will tend to have tailored backbones as well. A common backbone can be designed in numerous ways, with ATM as a common example of a transfer mode today. In principle, it should be possible to connect all types of accesses and other backbones to this network. A balanced traffic engineering and dimensioning with smooth scalability gives the best ROCE. A multi-service packet backbone network must be capable of handling different types of traffic with widely differing characteristics, for example: real-time traffic for person-to-person communication Internet traffic IP backbone ATM backbone SDH/SONET network Fibre network Figure 12.2 The wanted service classes and a common packet backbone structure today Packet Backbone Frame relay networks PSTN/ISDN IP/MPLS networks Radio access networks Ethernet Wireless access Source: ITU-T SG 13 networks ATM networks Figure 12.3 The era of the vertical networks offer many interconnect possibilities/needs PSTN/ISDN Rec. Q.931 network Q & X series Rec. Q.700 series Frame relay PSTN/ISDN Rec. 1.580 networks Rec. Q.2931, PNNI Rec. 1.555 M series Rec. IETF RFCs Rec. 1.580 ATM networks IP-based networks Wireless access Rec. Y.1310 ATM OSF & NM, M series Rec. OSF = Operating support function for Source: ITU-T SG 13 fra