quick links

technology
fasp™ versus FTP

The following graphs compare file transfer throughput and transfer time for fasp™ file transfer and FTP file transfer in typical network scenarios. All fasp™ and FTP benchmarks are for file transfer tests run within the Aspera labs. In each test, a 1-gigabyte file was transferred between commodity Pentium-4 computers running Debian Linux, using a standard Debian Linux implementation of FTP and Aspera Scp for fasp™ file transfer. A nistnet network emulator was used to simulate network round-trip latency and packet loss conditions typical on the Internet. Actual FTP throughputs will depend on the particular implementation of FTP used, the operating system, and the particular network loss pattern, but the results shown are typical.

fasp™ vs. FTP on gigabit metropolitan and wide area networks

Conventional TCP file transfer technologies such as FTP dramatically reduce the data rate in response to any packet loss, and cannot maintain long-term throughputs at the capacity of high-speed links. For example, the maximum theoretical throughput for TCP-based file transfer under metropolitan area network conditions (0.1% packet loss and 10 ms RTT) is 50 megabits per second (Mbps), regardless of bandwidth. The effective FTP throughput is even less (22 Mbps). In contrast, fasp™ achieves 100% utilization of high-speed links with a single transfer stream.

In the particular test shown, the fasp™ throughput on a gigabit ethernet MAN (509 Mbps) presses the disk read/write speed limits of the endpoint computers. Perhaps more important, fasp™ maintains this throughput even as latency and packet loss increase (505 Mbps at 200 ms/2%). FTP throughput degrades to about 550 Kbps under the same conditions. While this 1000X speed advantage over traditional TCP transfers is only evident on the fastest long-haul networks, it illustrates the difference in the fasp™ approach.

 fasp™ vs. FTP on cross-continental links

Aspera fasp™ sustains the highest possible end-to-end file transfer rates on cross-continental and intercontinental file transfers where latencies are high and packet loss is variable. An FTP file transfer from LA to New York (90 ms) will achieve 5-6 Mbps when loss is low (0.1%). As congestion on the link increases (1%), FTP dramatically reduces its rate to 1.4 Mbps. In contrast, fasp™ transfers data at link capacity. On a 155 Mbps link with 90 ms/1%, fasp™ transfers at 154 Mbps, 100 times faster than FTP. Using a more typical 45 Mbps link, the transfer is still 30 times faster than FTP.

fasp™ vs. FTP on intercontinental links

fasp™'s throughput advantage over FTP is more pronounced on an intercontinental transfer. At a packet loss rate of 2% and latency of 150ms, an FTP file transfer between continents runs at 700 kbps, and can drop to a crawl during periods of high congestion. fasp™ maintains stable throughput at link capacity in around-the-world file transfers. Using fasp™ file transport, a 1-gigabyte data transfer on a 10 Mbps link at 2% loss will run consistently at 9.9 Mbps, and finish in under 15 minutes, regardless of distance. On a 45 Mbps link, the transfer finishes in 3.3 minutes. An FTP transfer under the same conditions takes several hours, and may terminate prematurely.

fasp™ over high-delay satellite links

The high latency and bit error rates of satellite links severely hamper FTP file transfers, making large data set distribution or file upload over satellite impractical. fasp™ file transfer rates are immune to the distance and loss characteristic of single and multiple satellite hops. For example, a single fasp™ file transfer can fill a full transponder bandwidth (e.g. 45 Mbps) and will gracefully tolerate even the most extreme packet loss (over 30%), while FTP runs at 100 kbps or less and may not complete.

fasp™ vs. FTP on 802.11 Wireless

802.11 Wi-Fi and fixed wireless networks are proliferating. However the promise of uploading/downloading personal data, large email attachments, or images from a mobile endpoint is limited today by the poor performance of TCP-based file transfers over wireless links. File transfers using conventional FTP or HTTP over wireless achieve a fraction of the specified capacity and are prone to wide variations in throughput and early terminations, depending on the link quality. Early experiments show that fasp™ improves the throughput of file transfers over standard 802.11 a/b/g connections by a factor 1.5 -2 and is more robust to the changes in link quality due to roaming or other traffic. As shown in the graph below, FTP throughputs and transfer times vary by +/-20% while fasp™ runs faster and at a steady rate. The fasp™ throughput and reliability advantage over standard file transfer may become even more necessary as wideband wireless enters the mainstream.