On the Impact of Slicing Granularity on the Availability and Scalability of 5G Networks

5G networks will support network slicing to address the diverging needs of 5G applications. In this paper, we lay out a system model and mathematical framework to analyze the impact of resource granularity of network slicing on service availability and densification. We establish closed form expressions for service/slice availability in two extremum points of system operation that correspond to very fine and very coarse resource allocation for slice instances. We call the system operation around these extremum points as micro-slicing and macro-slicing regimes, respectively. Our analysis indicates that micro-slicing can achieve multiple orders of magnitude difference in service availability against macro-slicing even with as few as two slice types. Our results also indicate that in the short run, macro-slicing with resource over-provisioning is a viable approach to support few slice types at carrier-grade availability, but this approach fails to scale to higher densities of slice types. Another crucial outcome of our analysis is that the relationship between the slice availability and resource granularity (of slice instances) is not monotonic due to a quantization effect. Thus, rather than adopting a gradual reduction in slice instance sizes, system architects should consider moving directly into the micro-slicing regime in order to support higher service densities in 5G cloud.