n as cheaply as possible, regarding CAPEX and OPEX (CAPEX and OPEX are explained in Chapter 4). This is illustrated in Figure 12.2. 12.2 SERVICE PLAN VERSUS PACKET BACKBONE See also Section 5.13 in Chapter 5, and many 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 netwo