On-the-fly TCP path selection algorithm in access link load balancing

Many enterprises install multiple access links for fault tolerance or bandwidth enlargement. Dispatching connections through good links is the ultimate goal in utilizing multiple access links. The traditional dispatching method is only based on the condition of the access links to ISPs. It may achieve fair utilization on the access links but poor performance on connection throughput. In this work, we propose a novel approach to maximize the per-connection end-to-end throughput by the on-the-fly round trip time (RTT) probing mechanism. The end-to-end RTTs through all possible links are probed by duplicating the SYN packet during the three-way handshaking stage of a TCP connection. The experiment results show that the ratio to choose the best outgoing access link is 79% on the average. If the second best link is chosen, it is usually very close to the best, thus averagely achieving 94% of the maximum possible throughput. The ratio of the traditional round-robin (RR) algorithm is only 35%, and the link selected by RR algorithm could provide 69% of throughput.