Centralized vs. distributed algorithms for resilient 5G access networks

Cloud radio access networks (C-RANs), relying on network function virtualization and software-defined networking (SDN), require a proper placement of baseband functionalities (BBUs) to reach full coverage of served areas and service continuity. In this context, network resources can be shared and orchestrated to meet the flexibility required by a dynamically evolving environment. Different methodologies, based on analytical formulation or heuristic algorithms, can be applied to achieve suitable trade-offs among cost components. This paper considers both centralized and distributed algorithms to obtain BBU hotel placement in C-RAN and compares their performance, scalability and adaptability to evolving scenarios. As expected, the results obtained with the distributed approach are sub-optimal, but very close, in most cases, to the optimal solutions obtained with a centralized algorithm based on integer linear programming. In addition to off-loading the SDN orchestrator, the distributed approach, differently from the centralized one, is shown to be able to cope with the evolution of the C-RAN topology with limited incremental changes in the original placement. The limits of the centralized approach in terms of scalability that the distributed approach is able to overcome are also evidenced.