yer. 12.4.2 CONTROL SPLIT Figure 12.9 shows an example of a border area functionality split between backbone connectivity control and call control. The exemplified standard (BICC) is described in Chapter 14. In the connectivity part the traffic resources are handled by means of bearer signalling. There are also QoS and security resources in the backbone. ISN is an interface- serving node, that is to say a gateway/edge node. This border area automatically brings the question of connectionless versus connection-oriented backbone network design. For pure data IP connectionless networks are fine. However, IP will apparently conquer a much broader range of services. If considering all the services according to Figure 12.2, Packet Backbone Management system Traffic system Control implemented for IN (Compare figure 8-7) Sevice layer Control servers Control layer Connection control CO, CL Connectivity layer Traffic resources Figure 12.8 The principle split between call control and connectivity layer functions ,======== Bearer Bearer signalling signalling TDM links Packet network TDM links PSTN/ISDN network BICC network PSTN/ISDN network Figure 12.9 The split in control between control and connectivity layers, as illustrated by means of BICC then connection-oriented design gives the best QoS and traffic engineering tools. This means that there is a need for connection-oriented IP network design, One of the most interesting standards is called multi-protocol label switching (MPLS). The reason for the name is that MPLS label switching can be achieved using any L2 protocol such as ATM, frame relay, Ethernet, and point-to-point links. An introduction to MPLS is presented in Chapter 7. The connection-oriented feature with paths is illustrated in Figure 12.10. The backbone is now defined as the lowest elliptical layer in Figure 12.11 with some additions indicated in the text below the figure: QoS, routing, numbering and security solutions in the backbone, and bearer signalling for path set-up. Regarding QoS, users will actually