X over bluetooth?

Richi Plana myopenmoko at richip.dhs.org
Mon Feb 5 05:45:15 CET 2007

On Sun, 2007-02-04 at 15:37 -0800, Mitch Skinner wrote:
> On Sun, 2007-02-04 at 11:39 +0100, Dr. H. Nikolaus Schaller wrote:
> > If you have IP networking over Bluetooth, you can directly access X11  
> > (and other client-server apps) without modifying it at all.
> > So, it appears to me to be a better solution to make the OpenMoko a  
> > wireless client of your LAN.
> Hence my question about how much overhead is involved with running
> networking over bluetooth (BNEP).  Does anyone have measurements on
> that?
> Mitch
> > > My question is, would it be better to use BNEP?  Or does BNEP impose
> > > some overhead that we could avoid by going over straight rfcomm?  It
> > > doesn't seem like a huge amount of effort to add bluetooth support  
> > > to X,
> > > though it might be a while before that was widely deployed.   
> > > Besides SDP
> > > support, what else would be involved?

The overhead is unsurprisingly very small for IPV4, typically 19 bytes
(versus Ethernet's 14). That includes the 4-byte L2CAP Header.[1] BNEP
supports Bluetooth Master-Slave logical links, as well, which is as
straight as straight goes (only 7 bytes overhead).

It would probably be worth it to implement a full IP stack, anyway. With
the screen resolution being so small and the user interface so slow, I
don't think Bluetooth will be much of a bottleneck. Energy consumption
will be pretty minimal, as well (someone wants to do the math?). And the
scenario would only be useful if your application just requires a dumb X
terminal. All the other devices on the phone would either not be used or
you'd have to write special X drivers for them.

[1] Based on BNEP 0.95a

Richi Plana

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