On control parameters for segmented file download using PR-SCTP unordered delivery

As wireless networks have pervaded as an access network to the Internet, various contents are delivered also on them. However, the performance of wireless networks suffers from sudden fading or shadowing. When we use TCP for downloading large files as usual, its performance often decreases due to the following three major TCP features: shrunk window size which is caused by congestion avoidance feature, binary backoff for retransmissions, and strict in-order delivery on single channel. In order to alleviate the second problem, our research group already proposed a segmented file download method which uses PR-SCTP multi-stream function to cancel retransmissions with too long timeout value. However, the control parameters have not been enough discussed on the method and unordered delivery which is defined in SCTP specifications is preferred to multi-stream since the segmented files can be reordered after the donwloading process. In this paper, the control parameters such as the number of concurrent requests and the timeout value for retransmission of request are discussed and some automatic tuning method is introduced for the segmented download using PR-SCTP unordered delivery.