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in a case of huge round trip delay a simple TCP window increasing is not an effective solution.I was facing a similar problem some years ago while my colleagues were transferring big files from India to Germany via FTP.
I can say, years ago, had a single TCP flow, between USA and Germany, that throughput increased 4X after increasing receiving host's receive buffer 4x. In your case, you know the flow had absolutely no drops?
What really helped there was a client supporting mutlisession file transfer.
Indeed it can, as multiple TCP flows can "ramp up" concurrently. A few data transfer utilities can do this automatically.
PS:
BTW, newer TCP stacks often advertise much, much larger receive windows then they did years ago. I.e., manual tuning of the host's TCP receive window isn't necessary. However, it's often worthwhile to confirm this is the case.
