Combined Virtual Mobile Core Network Function Placement and Topology Optimization with Latency Bounds

In this paper, a novel mathematical optimization model for virtual mobile core network embeddings with respect to latency bounds is presented. This formulation differs from the classical virtual network embedding (VNE) model as the virtual network topology (i.e. The allocation of e.g. eNodeBs to single core gateways) is not known in advance but subject to optimization. Our formulation can be regarded as network functions/service chaining approach [1] as it relies on the joint embedding of individual core network service chains where a core network service chain denotes the sequence of mobile core virtual network functions (VNFs) a user or control plane traffic flow traverses. Regarding the placement decision of virtual core network functions, we consider upper bounds for the latency caused by processing, packet queueing and propagation. It is assumed that the queueing and processing delay depends on the user/control plane traffic utilization of the node/virtual machine on which the respective VNF is executed and that the propagation delay is proportional to the path length of the respective user/control plane traffic flow. The performance of the proposed optimization model is evaluated for the case of the European example network topology NOBEL-EU as physical substrate network, taken from SNDlib [2].