Talkiet: The 100% honest answer is that I don't know... I'm relatively sure that ANY level 1 helpdesk from any ISP would be flummoxed by this clearly complicated or subtle issue. I have worked on issues before where unexpected performance (that was still well in excess of what would be considered reasonable BB performance) was observed - just because it was unexpected... Often unexpected performance is an early indicator of a problem, even if at an absolute level it's still fine for 99.99% of people.
Have you tried using this:
Plug in the values you know and see what you get...
Cheers - N
Plugging in my default window size of 131071 bytes and the observed ping of 159ms gives a result of about 6.5mbit/sec.
While I appreciate the link (it's better presented than I've seen thus far), it's just doing the match that was explained early on in this thread.
The fact of the matter is that I don't see 6.5mbit/sec, which I would expect with no tweaking. And I have taken the window way up to 512k (and at places in between) - which should be good for some 33mbit/sec (which is beyond the capability of my connection).
The fact of the matter is I've only seen better performance by running multiple connections.
TC (Gary) has stated again and again that they do not shape packets. Their BB & Media architect has reiterated they do not mess with packets in any way. TCPDumps confirm the sliding window TCP options arrive intact. I've done about every test that can be done without having deep access to TC's network.
Oh, and I think you've earned the retraction and apology I offered above. :-)