A Desperate Plea for a Free Software Alternative to Aspera (2018)
Ex Aspera Dev here. I did the encryption and early parallel work.<p>There is a lot of good science behind fasp. An advantage it has over IETF protocols is that both ends trust one another. Another advantage, until recently, was out-of-order delivery.<p>The protocol totally ignores drops, for flow control. Instead, it measures change in transit time. The receiver knows, the sender needs to know, but the useful lifetime of the measurement is less than the transit time. This should make an engineer think "control theory!", and did. So, the receiver reports a stream of transit time samples back to the sender, which feeds them into a predictor, which controls transmission rate.  Simple, in principle, but the wide Internet is full of surprises.<p>If you think this wouldn't be able to go a thousand times faster than TCP, you have never tried moving a file to China or India over TCP. :-) (Customers used to report 5% drop rates.) Drops and high RTT are devastating to traditional TCP throughput on high-packet-rate routes; read about "slow-start" sometime, and do the math. Problem is that for untrusted peers, drops are the only trustworthy signal of congestion. Recent improvements where routers tag packets to say "I was really, really tempted to drop this!" help some.<p>Torrents get the out-of-order delivery and the lower sensitivity to drops, but its blocks are too big.. Others commented that opening lots of connections gets around some TCP bottlenecks, but that helps much only when the drop rate isn't too high (i.e. not to India or China).