and the system rolled back to the conditions before the new request was received. Type B2 uses the PrU compensation approach of Liu et al. [56], but it can be seen that this protection is incomplete; although the loss of PrUs is small it is still finite SO isolation is not achieved completely. The reason this performs much worse, in that sense, than the PrU compensation mechanism in Liu et al. [56] is that all the users are priority users, apart from the single new user being added, SO there are insufficient free RBs to perform the compensation. Type C2 is provided purely as a comparison with C1 by omitting rollback. As with B, not including rollback means that the implicit isolation is not 100%, although there is a greater number of QUs overall since some of the new users will have better channel conditions than the PrUs. Another effect of the protection is shown in Figure 8.18 where the need to ensure isolation shows there is a waste of RBs - the B1/C1 types with rollback prioritize isolation at the expense of allocating all the RBs. However, the waste is relatively small, of the order of 12%, but it is a price that must be paid for the isolation. These results are for cases where, once a user is allocated enough RBs to achieve its desired SINR, it is never removed from the network. In a realistic case, users only have a finite connection time, SO at some point they will terminate their connection. This is demon- strated in Figure 8.19 for a single example run using Type C1 where after 700 requests from 2% of the PrUs are randomly chosen to terminate their connection SO that the RBs released can then be used for new users as shown. The conclusion of this example is that CAC is a very effective means of maintaining iso- lation between slices, the rollback mechanism (i.e. not allowing any changes) achieving Total number of QUs recovered as new users are added 2% of PrUs terminating Cumulative number of requests Figure 8.19 Example of dynamic change to number of PrUs ©IEEE. 8 Network Slicing with Spectrum Sharing 