[ale] USB 2 RJ-45 adapter

[ahuitzot at mindspring.com]

On Fri, 20 Dec 2002 13:16:49 -0500 "David S. Jackson" <dsj at sylvester.dsj.net>
wrote:

> On Fri, Dec 20, 2002 at 06:40:25PM +0000
> cfowler  wrote:
> > 
> > Will not work.
> > 
> > This type of modem requires a direct plug
> into a PC.  
> 
> 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.

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?

> 
> An adapter that connects to a PC USB port can
> translate to an RJ-45
> socket back and forth.  Is it a power problem
> (adapter gets power from
> the PC/notebook USB port)?  Can't the adapter
> get power from the DSL
> modem as well?

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.  

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
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