s to the LSP rather than inspecting the DSCP (which is hidden in the IP packet header). A second approach used by MPLS is to assign different DiffServ classes to the same LSP but make use of the three Exp (experimental) bits in the shim label to allocate up to eight PHBs. While it can be seen that MPLS can support the mapping of DiffServ classes into labels, this in itself does not pose a great advantage. A more significant advantage of MPLS is that traffic-engineered trunks can be used between edge nodes in the MPLS network. In this way it is possible to dimension the network with tighter tolerances than is possible with a con- ventional IP DiffServ solution. Typically the trunks will be set up using RSVP-TE between customer endpoints and will have QoS parameters that match the customer's Service Level Agreement (SLA). Because the RSVP-TE LSPs allocate resources (typically datarate) it is possible for routers and network management systems to keep track of committed resources in the network. Then, as new traffic trunks are requested, it is possible to plan the network dimensioning appropriately through assigning the trunks to appropriate paths. This requires resource-oriented traffic engineering that IP cannot easily provide but MPLS can. Resource-Oriented Traffic Engineering Resource-oriented TE is generally concerned with configuration of paths through the network such that network utilization is maximized. To achieve this usually requires paths to be placed according to resource awareness, not just topology, and the paths must be con- nection oriented. This is difficult to apply to conventional IP, which uses a shortest-path route and a hop-by-hop approach. As a simple example to demonstrate the problem, con- sider the scenario shown in Figure 13.13. Here there are two different traffic requests made on the ingress to the network at A and B toward router F. Conventional IP routing will select the shortest path through the network such that the route from C to F will be C, E, F. Clearly Chapter 13 Multiprotoco