Dropping policy for improving the throughput of TCP over optical burst-switched networks

Burst loss due to contention in Optical Burst-Switched (OBS) networks significantly degrades the throughput of TCP sources in the local access networks because TCP congestion control mechanism makes a TCP source enter a slow start phase regardless of the congestion degree of OBS networks. In this paper, to improve TCP throughput over OBS networks, we first introduce a dropping policy (DP) with retransmission of the bursts dropped due to contention, by the ingress node. Then, we extend the DP with retransmission to drop a burst that has experienced fewer retransmissions in the event of contention in order to reduce the number of events that a TCP source enters the slow start phase due to contention. Additionally, we propose to limit the number of retransmissions of each burst to prevent severe congestion. For the performance evaluation of the proposed schemes, we provide an analytic model of TCP throughput over OBS networks. It is shown via numerical and simulation results that the proposed schemes can achieve better TCP throughput performance than an existing DP without retransmission.