hors explain that all slices can run on the same shared infrastructure, or on separate infrastructures as the operator requires, and this is a much more flexible solution than a single physical network. 8.3 Network Slicing in the RAN Points to note about network slicing: A network slice provides a set of network capabilities and performance levels that may be suitable for a set of service types. A service must be mapped to at least one slice, but it may also be mapped to more than one slice. A network slice may be used by only one particular service type, or it may handle several types. The service type may represent more than just the normal concept of a service: for example, a mobile virtual network operator (MVNO) may be restricted to one or a limited set of slices by the physical network operator. In fiber networks the problem of having independent "logical pipes" with no interfer- ence between them is fairly easy to solve, but slicing in the RAN [24-27] is much more challenging as (i) that usually provides the constraint on resource availability and (ii) it is more difficult to prevent interference. The RAN can be logically divided to provide flexibility for different services and user requirements, potentially leading to significant cost savings [28, 29]. Figure 8.7 shows the concept of network slicing. Here, for simplicity, the spectrum allo- cated to an operator is shown as a contiguous block that is divided into slices with no gaps, but realistically a slice could comprise spectrum with gaps and split across different fre- quency bands. Notice that the network slicing concept of Figure 8.7 is very similar to spectrum sharing (e.g. Figure 8.4), but the entities sharing are not necessarily different operators: they could be users with different QoS requirements. The simplest form of slicing is to have separate allocations of spectrum to each slice; if this allocation is fixed, this guarantees resource allocation to the slices but does not allow for dynamic changing demand or for unequal load distributions.