Elastic Routing Table with Probable Performance for Congestion Control in DHT Networks

Structured P2P (DHT) networks based on consistent hashing functions have an inherent load balancing problem. The problem becomes more severe due to the heterogeneity of network nodes and the non-uniform and time-varying file popularity. Existing DHT load balancing algorithms are mainly focused on the issues caused by node heterogeneity. To deal with skewed lookups, this paper presents an elastic routing table (ERT) mechanism for query load balancing, based on the observation that high degree nodes tend to receive more traffic load. The mechanism allows each node to have a routing table of variable size corresponding to node capacities. The indegree and outdegree of the routing table are also adjusted dynamically in response to the change of file popularity and network churn. Theoretical analysis proves the routing table degree is bounded. The elastic routing table facilitates locality-aware randomized query forwarding to further improve lookup efficiency. By relating query forwarding to a supermarket customer service model, we prove a 2-way randomized query forwarding policy leads to an exponential improvement in query processing time over random walking. Simulation results demonstrate the effectiveness of the elastic routing table mechanism and its related query forwarding policy for congestion and query load balancing. In comparison with the existing “virtual-server”-based load balancing algorithm and other routing table control approaches, the ERT-based congestion control protocol yields significant improvement in query lookup efficiency.