backbone and radio resource control units. In the framework of the IaaS, each or the combination of some of these advanced 5G features can be viewed as one kind of services offered by the InSPs, and then can be virtualized to the NSPs or anyone who needs them [@Trakas].

### Radio-Access-as-a-Service (RAaaS)

When the whole RAN is decoupled, the infrastructure and radio access can be treated separately, which motivates the novel concept of RAaaS, where some RAN functionalities belonging to the protocol stack of the radio interface can be viewed as a service. In light of RAaaS, all the software related components, such as signalling, access and admission control, radio network controller, gateway, and many other protocols in the RAN or core networks, are virtualized. All of these RAN functionalities, or part of them, may then be offered as a service by the RANaaS platform to the NSPs, which adapts, configures, and extends their operation to current traffic demands and keeps up with the backhaul and access network structure requirements.

### Radio-resources-as-a-Service (RaaS)

In the virtualized networks, after abstracting, isolating and slicing, scalable radio resources can be better controlled and optimized, and may be pooled independently of the location, and 