Evaluation of hierarchical DHTs to mitigate churn effects in mobile networks

• This research reviews recent works on flat DHTs under high churn.
• This research evaluates a flat DHT and a hierarchical DHT with or without churn.
• This research assesses the performance of two HDHTs with or without churn.

Existing flat peer-to-peer (P2P) systems based on distributed hash tables (DHTs) perform unsatisfactorily under churn due to their non-hierarchical topology. These flat DHTs (FDHTs) experience low lookup success ratio, high lookup latency and high bandwidth usage as a consequence of the presence of churn. With this, we explore the use of hierarchical DHT (HDHT), specifically the superpeer design, in mitigating the effects of churn. To the best of our knowledge, we are the first to intensively examine HDHTs with and without high churn through simulations.Using the OMNeT++ simulator and the OverSim framework, we analyze flat and hierarchical DHTs with and without churn. Results show that the implemented HDHTs perform more satisfactorily than a flat DHT because of better fault isolation and smaller cluster sizes at the cost of higher superpeer traffic. HDHTs are more stable as they have better lookup success ratios. They are more efficient as evidenced by lower lookup latencies and lower average node bandwidth usage. They are more scalable since their performance do not degrade significantly even at high population. With this, the implemented HDHTs can be utilized to alleviate the effects of churn in mobile networks.