utilization of cloudlet and mobile cloud processing, etc, which can help to reduce traffic amount on the fronthaul or backhaul, also release the abundant on central data processing units.

Service Composition
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In order to run a network or provide QoS-guaranteed services directly to the end-users, a NSP needs to acquire from different InSPs in the XaaS framework. Such a inherit nature of XaaS essentially requires to enable the service composition. For example, when a end-user needs to watch a stream, different InSPs may be asked from the NSPs to provide caching capability, radio resource, infrastructure, and network functionality. Accordingly, the proposal and investigation for energy and cost efficient service composition will play a central role in supporting and coordinating the XaaS framework.

Specifically, as loose-coupling among services is one of the critical concepts in the XaaS and there are a large number of services involved in the XaaS, scalability emerges as one topic with research significance for service composition design. Accordingly, how to take into consideration of different needs to compose multiple services and maintain QoS requirements of different parties are of research importance. Besides, heterogeneity is another challenging issue to service composition. The services that are provided to 