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On May 9, 2022, at 12:31 PM, Tomasz Moń <deso...@gmail.com> wrote:
> There is no such thing as "low-speed bus" because low-speed is only
> allowed for non-hub devices. USB hosts and hubs *must* support atleast
> full and high speed. USB devices are allowed to be low-speed (such
> devices can operate *only* at low speed).
So what is the term used for a cable between a low-speed-only device and either
a host or a hub?
The USB 2.0 spec appears to use "bus" for an "edge", in the graph-theory sense:
https://en.wikipedia.org/wiki/Glossary_of_graph_theory#edge
rather than for the entire tree.
What *is* the correct term to use for a single cable, the traffic on which one
might be sniffing?
> It is important that the analysis engine know whether the packets were
> full or low-speed as there are slightly different rules. There is not
> so clear distinction between layers as USB does not really use ISO/OSI
> model.
>
> So I think it definitely makes sense to have separate link types for
> full-speed and low-speed.
It makes sense to indicate whether packets are full-speed or low-speed; nobody
is arguing otherwise.
The question is whether the right way to do that is to have separate link
types, so that you can't have a mix of full-speed and low-speed packets in a
single pcap capture or on a single interface in a pcapng capture, or to have a
single link-layer type with a per-packet full-speed/low-speed indicator.
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