Re: Speed specific Link-Layer Header Types for USB 2.0

[Tomasz Moń via tcpdump-workers <tcpdump-workers () lists tcpdump org>]

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>
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> From: Tomasz Moń <desowin () gmail com>
>
> Date: Mon, 09 May 2022 21:40:47 +0200
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> On Mon, 2022-05-09 at 12:02 -0700, Guy Harris wrote:
> > On May 9, 2022, at 7:41 AM, Tomasz Moń <desowin () gmail com> wrote:
> >
> > > That would require defining pseudoheader that would have to be
> > > included in every packet.
> >
> > Is that really a great burden?
>
> I think it would make it harder to understand the protocol for
> newcomers that use tools like Wireshark to try to make sense of USB.
>
> > > And it would only solve the corner case that the
> > > currently available open-source friendly sniffers do not presently
> > > handle.
> >
> > The point isn't to just handle what currently available open-source
> > friendly sniffers handle.  I'd prefer to leave room for future
> > sniffers that *do* handle it.
> >
> > > I think it is fine to assume that any tool that would create full-
> > > speed
> > > captures that contain both full-speed and low-speed data should be
> > > able
> > > to write pcapng file (or simply create two separate pcap files).
> >
> > I think that, if you're capturing on a link between a full/low-speed
> > host and a full/low-speed hub, with low-speed devices plugged into
> > that hub, it would not make sense to treat that link as two
> > interfaces, with one interface handling full-speed packets and one
> > interface handling low-speed packets; I see that as an ugly
> > workaround.
> >
> > So I see either
> >
> >         1) a link-layer type for full/low-speed traffic, with a per-
> > packet pseudo-header
> >
> > or
> >
> >         2) don't support full/low-speed traffic capture, just support
> > full-speed-only and low-speed-only traffic capture
> >
> > as the reasonable choices.
>
> The choice number 2 is essentially what the OpenVizsla does.
>
>
> --- End Message ---
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