A Chunked File Transfer Method Dynamically Selecting One from TCP and UDP According to Network Conditions

Nowadays, various contents are provided on the Internet as user´s access lines become much broader. In general, most of file transfer applications use TCP on the Internet. Since TCP performance has low tolerance to packet losses, UDP-based file transfer methods which guarantee the reliability of transmitted data by application layer protocols have been proposed. Since UDP does not have congestion control mechanisms inherently, the methods can influence other traffic when congestion occurs. Therefore, we propose a file transfer method which dynamically selects one from TCP and UDP with according to the network condition estimated by the observed packet loss ratio for two constant rate probing UDP flows. As a result, the proposed method shares bandwidth with other flows fairly by selecting TCP when the congestion occurred and yields high performance by doing UDP when the bit error rate is high.