My story was not an unusual one: I had just upgraded from ISDN to cable modem. Going to one of the bandwidth test sites, I confirmed that I was indeed getting 1.5 Mbps of throughput. A couple of days later, I downloaded a 150 MB file from a company in England to review. This should have taken about 15 minutes, but in fact, it took almost two hours. At the time, I assumed that their server was overloaded, or that there was a high degree of network congestion somewhere in between us. It was probably something else entirely, however.
TCP, the transport protocol underlying both FTP and HTTP, is sensitive to both latency and packet loss. As latency and packet loss increase, throughput goes down rapidly. With a 140 millisecond round trip time (RTT) and .03 percent packet loss, FTP maxes out at about 4 Mbps. With 360 ms RTT and .03 percent packet loss, it tops out at about 1 Mbps. With 360 ms RTT and 1 percent packet loss, FTP can't do better than 256 Kbps or so.
Digital Fountain has a product designed to help with this. Transporter Fountain 2.0 replaces FTP with an entirely different transport protocol not sensitive to either packet loss or latency. It uses a technology Digital Fountain calls Meta-Content, which basically is similar to RAID. A file is divided up in a fashion using parity so that all the packets contain enough information that the whole file can be re-created as long as most of the packets are received.
Transporter Fountain requires a 1 MB program to be loaded on the client. The program is available for Windows, Solaris, and Linux and will not provide much benefit if either the client or server have connections with less than 500 Kbits of throughput, or with file sizes under 100 MB. Within those limitations, the Transporter Fountain can deliver files at the maximum bandwidth that the WAN supports.
We received the TF3000 Transporter Fountain for testing. The 2U appliance is based on a Compaq server running RedHat Linux. It supports T-3 and higher connections, from 45 Mbps to 70 Mbps, and came with two 10/100 interfaces, six 36 GB hard drives, dual power supplies, a remote interface board that supports remote administration, including remote power on/off or reboot. Setting up the system was simple. The initial configuration can be done via serial terminal, or by attaching a keyboard and monitor. Once the initial network configuration is done, the rest of the configuration can be completed via a Web browser.
Source: Digital Fountain
Basic configuration is also quite simple. Although the manual is unclear on several configuration parameters, the on-screen help suffices. Files can be copied directly to the server one at a time. Transporter Fountain can also mount directories on other servers, poll those directories, and add any new files that are added to those directories. Files can be delivered by request from the client, or they can be pushed to other locations automatically. Other configuration parameters involve setting bandwidth limits on files as desired. Bandwidth Caps limit the maximum throughput of individual clients, while Tunable Rate Control offers the capability control Fountain traffic relative to other applications.
Once the server was configured, we set up a network impairment device that simulates a WAN connection using Shunra's Storm software. We tested both FTP and Transporter Fountain at three typical WAN speeds, 1.5 Mbps, 10 Mbps, and 45 Mbps, with five levels of packet loss: zero, .025 percent, 1 percent, 2 percent, and 4 percent, and three RTTs: 30 ms, 150 ms, and 300 ms. As packet loss and RTT went up, throughput with FTP went from the speed of the WAN link at zero packet loss and 30 ms RTT, to less than 200 Kbps at 300 ms RTT and 4 percent packet loss, even over the 45 Mbps connection. With Transporter Fountain, throughput was consistent with the speed of the WAN link, regardless of the level of packet loss or RTT.
For redundancy, multiple Fountains can be set up and a pool created. Clients can then download from any available Fountain, and fail over to another Fountain in the pool if necessary. Clients can even download from multiple Fountains simultaneously, further improving throughput.
How effective Transporter Fountain will be will depend greatly on the RTT and packet loss in your WAN. With short RTTs and zero packet loss, there is little benefit to the product. On the other hand, any company with offices on more than one continent is very likely to quickly amortize the device. The Internet Traffic Report (ITR) Web site www.internettrafficreport.com reports 0 to 6 percent average packet loss globally for June 2002. With typical RTTs, of just over 200 msec and 2 percent loss, FTP throughput is limited to 280 Kbps, no matter what the WAN connection supports.
|Model No.||Content Output||Size||No. of Concurrent Clients Included|
|Transporter Fountain 500||2 Mbps (T1/E1)||1U||Up to 5|
|Transporter Fountain 1000||10 Mbps (fractional T3)||1U||Up to 10|
|Transporter Fountain 3000||45 or 70 Mbps (T3)||2U||Up to 20|
Price of Server Setup as Tested: $95,000 (for the Transporter Fountain 3000)
Pros: Accelerates file transfers by five to 200 times, depending on WAN conditions;
Simple to deploy;
Provides bandwidth limiting on a per-file basis
Cons: A special client is required (although it is only 1 MB); Won't produce much benefit with files under 100 MB, or with client connections under 500 Kbps; The manual is generic for several versions of Transporter Fountain, and the syntax for some commands was incorrect for the version of Transporter Fountain we tested