Software-Defined Networking 2

4Adaptive and Continuous Consistency for Distributed SDN Controllers: Anti-Entropy Reconciliation Mechanism

4.1. Introduction

Logically centralized but physically distributed SDN controllers are mainly used in large-scale SDN networks for scalability, performance and reliability reasons. These controllers host various applications that have different requirements in terms of performance, availability and consistency. Current SDN controller platform designs employ conventional strong consistency models so that the SDN applications running on top of the distributed controllers can benefit from strong consistency guarantees for network state updates.

However, in large-scale deployments, ensuring strong consistency is usually achieved at the cost of generating performance overheads and limiting system availability. This makes weaker optimistic consistency models, such as the eventual consistency model, more attractive for SDN controller platform applications with high availability and scalability requirements. In this chapter, we argue that use of the standard eventual consistency models, though a necessity for efficient scalability in modern SDN systems, provides no bounds on the state inconsistencies tolerated by the SDN applications.

To remedy this, we propose an adaptive multi-level consistency model for the distributed ONOS controllers following the notion of continuous and compulsory (Yu and Vahdat 2000) eventual consistency, in which network application states adapt their ...