On Thu, 2006-07-20 at 08:52 -0700, Philip Levis wrote:
> On Jul 19, 2006, at 8:10 PM, Behcet Sarikaya wrote:
>
> > I agree with Phil, I think we should have his consideration
> > considered seriously.
> > Regarding his question, in the format draft, 802.15.4 MAC layer is
> > assumed and the frame sizes are from IEEE standard. This WG assumes
> > that even the light sensors support 802.15.4 MAC (kind of like
> > Telos motes). In that sense this WG is addressing futuristic sensor
> > nodes on which IP stack can be implemented. How close that future
> > be, we do not know.
> >
>
> You can totally write an IP stack -- even a TCP stack -- on sensor
> nodes today, admittedly the ones that have the biggest
> microcontrollers you can buy (atmega128L, MSP430F1611, etc.). The TCP
> stack might not have a lot of RAM for windowing and high performance,
> but that's rarely the goal. You can do it.
We have already built an 802.15.4MAC/AODVtiny/IPv6/UDP stack that will
run on a 64K part and, with some optimization in the MAC, should run on
a 32K part. For a non-routing node (read RFD) it should run on a 16K
part! As Phil rightly points out, RAM is actually more of a constraint.
>
> I don't think the requirements the document implies are unrealistic
> or onerous. As I said, you have to cut the line somewhere. My comment
> was just that they *do* preclude smaller nodes whose storage cannot
> hold a complete IPv6 packet, and it might be useful to note as such,
> since the document is defining the problem statement, and therefore
> the problem scope.
There certainly could be a problem for very small parts (ie those with
very limited RAM - 2k) where it could be nearly impossible for the
device to store a complete 1280 byte IPv6 packet, but I think with some
judicious use of memory it might be doable even on a 2k ram device so
long as it isn't trying to maintain routing tables.
geoff
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