A simple cross-layer approach to reduce duplicate acknowledgements for TCP over WLAN

TCP was designed to perform on wired networks, where packet loss is mostly caused by congestion, as compared to wireless networks, where losses due to error in channel are more likely. Hence TCP respond to all kind of losses by invoking congestion control and avoidance schemes resulting in performance degradation. Several solutions for the improvement of TCP over wireless link have been proposed which are divided into four broad categories, namely, transport layer, link layer, cross layer and split connection schemes. Wireless link layer protocol 802.11 is required to receive acknowledgment of every frame it sends, which is too conservative. This paper presents an improved delayed-ACK for wireless LANs (IDAWL), a new cross layer approach which reduces acknowledgments at link layer which a sender get, hence it eliminates the duplication of acknowledgement at link layer and transport layer. It is variation of DAWL in which ACK number of the TCP-ACK is sent at a MAC level and TCP ACK is discarded. This cross-layer approach leads to the local generation of the TCP acknowledgment of the downstream TCP data at the access point (AP). The performance of the proposed scheme is evaluated over NS-2 by comparing it with IEEE 802.11 and DAWL. The results show a significant improvement in TCP goodput.