In a recent press release (http://www.nasa.gov/press/2013/october/nasa-laser-communication-system-sets-record-with-data-transmissions-to-and-from/#.UmkyxPlwrng) NASA announced that now they have a 622 Mbps Laser link to the moon.
The press release also mentions that NASA was also able to transfer data at 20Mbps from earth to the space craft via this link.
I’m wondering what effective rate was NASA getting when transferring data on this link? The data should be transferring at the theoretical limit of 622Mbps.
At an average distance of 380,000 kms from Earth, it takes the signal (speed of light) just over 2 seconds to go to the moon and back (2500ms to be exact). This latency for sure will negatively affect any data throughput. Using our FTP vs. FC Calculator, we calculated that the maximum throughput for any TCP protocol including FTP on 622Mbsp link with 2500ms is 80Kbps. Yes that’s with a “K” yikes!!
I’m sure that NASA increased the TCP window size and used some acceleration techniques beyond the regular TCP configuration. But what was their effective file transfer rate from the moon?
We couldn’t resist testing this scenario with our FileCatalyst accelerated file transfer protocol. In our lab using a WAN network emulator from Apposite Technologies, FileCatalyst HotFolder and FileCatalyst Direct Server. We used the following parameters:
- Bandwidth: 622Mbps
- Delay: 3000ms +/- 150 ms (for jitter)
- Packet loss: 5% (NASA mentions negligible network loss)
The Result: About 602Mbps. That’s 95% link utilization, the other 5% is the pocket loss! See the screen capture below: