# Towards adaptive state consistency in distributed SDN control plane

## TL;DR

This paper proposes an adaptive consistency model for distributed SDN controllers that balances strict synchronization and eventual consistency to improve performance in large deployments.

## Contribution

It introduces a novel cost-based adaptive consistency approach combining strict and eventual synchronization for SDN controllers.

## Key findings

- Simulation shows performance improvements with the adaptive model.
- Critical operations are synchronized strictly, reducing delays.
- Less critical updates are propagated periodically, enhancing scalability.

## Abstract

State synchronisation in clustered Software Defined Networking controller deployments ensures that all instances of the controller have the same state information in order to provide redundancy. Current implementations of controllers use a strong consistency model, where configuration changes must be synchronised across a number of instances before they are applied on the network infrastructure. For large deployments, this blocking process increases the delay of state synchronisation across cluster members and consequently has a detrimental effect on network operations that require rapid response, such as fast failover and Quality of Service applications. In this paper, we introduce an adaptive consistency model for SDN Controllers that employs concepts of eventual consistency models along with a novel `cost-based' approach where strict synchronisation is employed for critical operations that affect a large portion of the network resources while less critical changes are periodically propagated across cluster nodes. We use simulation to evaluate our model and demonstrate the potential gains in performance.