Optimising Virtual Network Functions Migrations: A Flexible Multi-Step Approach
Nguyễn Tuấn Khải, Andreas Baumgartner, Thomas Bauschert · 2019
In this paper, we introduce a novel optimisation model for virtual network functions (VNFs) migration in multiple steps. Since VNF migration can be enabled by VM migration, we model the course of VM migration by applying the concept of time-expanded networks. Our model is related to virtual network embedding (VNE), i.e., the problem of mapping virtual networks, or service chains (SCs), onto a capacitated substrate network. Contrary to the classical static VNE problem, we focus on finding an optimum transition from one mapping to another through one or multiple intermediate mappings. The concept of multi-step VM migration was first introduced in a previous publication, in which a fixed migration deadline per step was imposed. In this paper we remove this restriction, making the migration model more flexible. The VNF migration problem is formulated as a mixed integer linear program (MILP) and solved by a commercial solver. The performance of our new approach is evaluated via simulations assuming a realistic substrate network topology and SCs. The results show significant performance improvements w.r.t. migration time, failure sensitivity, feasibility, and cost of migration, especially in the case of high network utilisation.