Improving file transfers using SCTP multistreaming

We identify overheads associated with FTP, attributed to separate TCP connections for data and control, non-persistence of the data connections, and the sequential nature of command exchanges. We argue that solutions that avoid these overheads using TCP place an undue burden on the application. Instead we propose modifying FTP to use SCTP and its multistreaming service. FTP over SCTP avoids the identified overheads in the current FTP protocol without introducing complexity at the application, while still remaining "TCP-friendly". We implemented FTP over SCTP in three ways: (1) simply replacing TCP calls with SCTP calls, thus using one SCTP association for control and one SCTP association for each data transfer, (2) using a single multistreamed SCTP association for control and all data transfers, and (3) enhancing (2) with the addition of command pipelining. Our experiments compared these 3 variations with the classic FTP over TCP. Results indicate significant improvements in throughput for multiple file transfers with all three of our variations. The largest benefit occurs for (3) FTP over a single, pipelined, multistreamed SCTP association. More generally, this paper encourages the use of SCTP's innovative services to benefit existing and future application performance and presents the case for multistreaming.