On Efficient VNF-FG Design in IoT Networks

In recent times, it has been witnessed that an increasing number of Internet connected devices impose an huge challenge on Internet of Thing (IoT) networks, which provides diverse and complex network services through edge computing empowered IoT terminals. A network service can be formally represented by Virtualized Network Function Forwarding Graph (VNF-FG) with the advent of Network Function Virtualization (NFV) technology. Previous researches mainly focus on VNF-FG embedding (VNF-FGE) and take VNF-FG as the input. In this paper, we investigate the design of VNF-FG, which is required to be a Directed Acyclic Graph (DAG) and achieved by the IoT terminal, in two scenarios. In static scenario, for a set of traffic flows arriving at the IoT terminal and requesting different network services, an ILP model Ps including loop prevention constraints is well formulated. An approximation algorithm AFGC with competitive ratio O(1+(|R|-1)α), α (0, 1) is then designed, which thoroughly search all key instances to run comprehensive loop break. In dynamic scenario for a flow request on the fly reaching an IoT terminal, an ILP model Pd and another approximation algorithm DFGU with a competitive ratio O(1 + |SCr||Fr| ) are developed, giving priority to reuse of existing topology to generate an augmented VNF-FG of minimum size. Simulation results indicate AFGC and DFGU outperform state-of-art work, and the gap between each of the two algorithms and their respective ILP models is marginal.