FDA: a novel base station flow control scheme for TCP over heterogeneous networks

A novel proactive base station flow control algorithm, called forced duplicate acknowledgement (FDA), is proposed for extending TCP over wireless networks. FDA is implemented at the base station (BS) of a wireless network. It works in conjunction with existing TCP enhancement schemes such as Snoop or New Snoop. In FDA, if the average occupied buffer size at a BS exceeds a pre-defined threshold, an incipient congestion is detected. Then three forced duplicate ACKs, functioning as a congestion notification, will be generated by the BS and forwarded to a set of selected TCP senders. Upon receiving the forced duplicate ACKs, a sender reduces its transfer rate as a result of performing the fast retransmit procedure. To prevent multiple packet dropping due to buffer overflow at the BS, a quality guaranteed cache release policy is designed. The idea is to make room for the on-the-fly packets by releasing some cached but not-yet-acknowledged packets at the BS in advance. The performance of the proposed FDA is evaluated by simulations. We found that under various traffic and system configurations, FDA can not only fairly allocate the available wireless bandwidth among all TCP connections, but also achieves the highest throughput as compared to other schemes we have investigated.