[ale] USB 2 RJ-45 adapter

[David S. Jackson]

On Fri, Dec 20, 2002 at 02:00:12PM -0500 ahuitzot at mindspring.com <ahuitzot at mindspring.com> wrote:
> > Why?  
> 
> Because a usb "device" is just that, its a device.  And a usb "host" is also
> just that, a host.  You cannot expect a device to act as a host under USB.  It
> just cant.  The protocol will not allow it.

Hmmm.  That makes a lot more sense.  Duh.  Kinda like client and server
I guess.

> Now, if it were firewire, it would be possible, but expensive to impliment
> because then the device would not only have to have enough smarts to do its
> job as a device, but it would also need the correct firmware and prossing
> power to act as a host as well.  A bit overkill for a simple USB->Ethernet
> dongle dont ya think?

Yeah, definitely.  :-)

> The way you state that makes it sound so simple (it also implies to me that
> you do not know how USB works...) its not that simple at all.  

I don't know how USB works; I certainly hope I don't sound as though I'm
pretending to know.  :-)

> USB has an underlying protocol of its own that each device must adhere to. 
> Its not simple like it used to be with Async serial devices, where if it
> talked serial, it talked serial and all was rosy and nice.  For example with
> serial devices, you can connect 2 computers together simple as pie, you just
> need a null modem cable and the correct terminal software and your talking. 
> That would be like connecting 2 USB hosts together, but thats not possible in
> USB without some special hardware in the middle (which you can buy BTW, its
> usually called a USB file copy cable, or a USB host to host cable).
> 
> You can do the same thing with 2 serial modems, you just connect them together
> with the correct cable, and they can talk to each other (you can even call
> one, then connect to it and have it send commands to the other to have it dial
> out).  You can't do this with USB devices.  Most of the time USB devices are
> dumb as rocks until they are connected to the computer because a small piece
> of firmware is uploaded to it when its enumerated (most of the USB->serial
> things are like this I think).  So that is the first obsticle you would have
> to overcome in usb device->device communication.  The second (and the biggest)
> is the USB protocol does not allow it.  If you wanted to devices to be able to
> talk to each other, someone would have to invent something like the
> afformentiond usb host->host device, that would act as a host that then talked
> to each device and acted as an intermediary between them.  This device would
> have to be very specific to the functions of the 2 devices you want to connect
> together however, either that or real expensive (meaning just use a computer
> to do it).
> 
> So see, USB is not as simple as you make it out to be :)
> 
> HTH,
> Mike

This definitely helps, Mike.  I was thinking about it simply, which
happens when you don't know what the hell you're talking about.  :-)
I'm glad this got posted to the list, because your explanation makes
crystal clear sense!  

-- 
David S. Jackson                        dsj at dsj.net
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