Availability and Failure Rate of VNF Instances: Impacting Parameters and Calculation Methods

Network Function Virtualization (NFV) defines a dynamic environment to deploy Virtual Network Functions (VNF) as constituents of Network Services (NS) that provide specific network functionalities. A VNF is composed of at least one VNF Component (VNFC) and zero, or more Internal Virtual Links (IntVL). The availability of an NS depends on the availability of the composing VNF functionalities. In turn these depend on the underlying resources, their placement constraints, policies, and their number, which change over time as required by the varying workload. Accordingly, the availability and failure rate of a VNF instance may vary over time. That is, it may be different for the different VNF scaling levels. In this paper, we investigate the parameters affecting the availability and the failure rate of a VNF instance, and we propose methods to calculate for such dynamic cases the guaranteed minimum availability and the guaranteed maximum failure rate for a VNF instance considering a given infrastructure.