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    Well-done consolidating all that in one place. I’ve gone looking for many of these details at different times more than once. I’ll be saving this link.

    This is the best-organized and most comprehensive presentation of these details that I’ve seen. And it does a tremendous job citing sources for the details presented. The USB Implementors Forum would be smart to take this, add more canonical citations for some of the points, and maintain it going forward.

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      A single line can either be simplex (unidirectional, transmitting in the same direction all the time) or half-duplex (alternating between directions).

      True in case of USB, but not in general. With some clever trickery you can have full-duplex over a single line. For example, gigabit Ethernet is implemented over 4 full duplex lanes, while there are only 4 lines in a Cat 5A cable.