TCP Upload and Download Fairness over IEEE 802.11 Wired-cum-Wireless Heterogeneous Networks

A scheme of setting a limit to the TCP sending window size is proposed to improve the TCP fairness between upload and/or download flows in wired-cum-wireless networks. The goodput and delay of the upload and download TCP flows are compared to evaluate the TCP fairness for different schemes, which are the different combinations of setting a limit (64 or 4) to the sending window size and using the delayed acknowledgement (ACK) scheme or not. Extensive simulation results and analysis show that (1) for TCP download flows, setting the limit of sending window size to 4 can improve the fairness; (2) for TCP upload flows, limiting the sending window size and using the delayed ACK strategy are both beneficial to fairness; (3) for TCP download and upload mixture flows, limiting the sending window size to a small value (e.g., 4) rather than using the delayed ACK strategy, is the solution to improvement of the fairness; (4) a large delay interval (200 ms or 300 ms) does not result in improvement in fairness and performance; (5) a larger TCP packet size (1 400 B) can improve the TCP upload goodput and decrease the download goodput; in contrast, a smaller TCP packet size (560 B) can increase the download goodput and decrease the upload goodput.