I've seen it both ways--although you are correct according to IEEE (of which I am a member anyway and as such I should probably try to make sure I don't stick my foot in my mouth when referencing their technical terms). This confusion is an obvious problem which arises from using poorly-chosen abbreviations. Either way, having 20MB/s is impossible without having a port which can transfer at speeds higher than 100mbps--which the 360 doesn't have.
Now, using my super hero skills of logical deduction, I will venture to guess that his FTP client uses MB/s as an abbreviation for megabit. (IMG:
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The most likely cause is that FileZilla is actually showing incorrect values - I use it, and while monitoring network transfer rates elsewhere, FileZilla often spikes the transfer speed even though it isn't actually transferring that fast.