[lug] USB to USB as serial connection

Tkil tkil at scrye.com
Tue Jun 29 17:17:51 MDT 2004

>>>>> "Nate" == Nate Duehr <nate at natetech.com> writes:

Tkil> No, because current USB is not capable of peer-to-peer operation
Tkil> (unlike firewire - but most p2p modes for firewire end up just
Tkil> implementing IP over it, so...)

I should have been more precise: current USB ports cannot act ina
peer-to-peer fashion with just a straight cable, and not with just
crossing wires either; they require active electronics on the wire.

Contrast this with firewire, which can use the same cable to talk from
a host to a client (say, my powerbook to an external HD) as can talk
from one host to another (from one powerbook in "target mode" to
another powerbook).  That said, it's not a true peer-to-peer, but that
is (so far as I know) a software limitation, not a hardware /
signalling limitation (as it is in USB).

>>>>> "Nate" == Nate Duehr <nate at natetech.com> writes:

Nate> I'm not 100% sure this is true.  I have a version of Norton
Nate> Ghost that will do peer-to-peer with a special USB cable between
Nate> two machines.

In this case, I believe that the "special cable" acts as a usb client
to both sides of the connection, which means that the actual topology
is something like:

   +---------+      +-------------------------+      +---------+
   |     host|      |client    link     client|      |host     |
   |pc1  USB =------=USB       cable       USB=------=USB   pc2|
   |     port|      |port      widget     port|      |port     |
   +---------+      +-------------------------+      +---------+

So each PC is still seeing only a single client device.  See:

   http://tinyurl.com/yuo8g  (link to symantic page)

The new(ish) standard for USB that I was thinking about is a
supplement to the USB 2.0 standard called "USB On The Go".  A nice
writeup seems to be this one:


Nate> I don't think it's very common to see the cable available in
Nate> local stores, though, and I'm not sure how they implement the
Nate> protocol.

Yeah.  In the current situation (just want fast transfer between two
computers) I'd consider a crossover ethernet cable, figuring that both
machines have at least 100mbps ethernet -- which is about 10x faster
than USB 1, and 1/4th as fast as USB2 / firewire.  If they both have
GigEthernet ports, then you don't even need a special crossover cable;
those ports should autosense what's going on.

At home, I tend to use netcat over wired / switched 100MBps and that's
fast enough for most of what I do.  I'm considering upgrading to GigE,
but that's mostly for huge transfers (150GB of MP3s from point A to
point B, tagging them remotely, things like that).


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