+1 in favor of using optimized DHCP if possible (no opinion on 'if
possible'), rather than inventing something new.
As I've shared with several people in private emails recently, it's
pretty clear that lowpan nodes are going to get more capable moving
forward, not less. Why? Radios don't scale down in area when you scale
CMOS processes. Today's 15.4 single-chip nodes are made in technologies
that are several (maybe five?) generations behind the cutting edge.
This makes economic sense because the sales volumes don't support the
need for expensive mask sets yet.
When there's a volume application, and someone puts a 5mm2 radio into
modern CMOS, it just doesn't make sense to put 48kB of rom/flash and
10kB of RAM next to it. You'll put hundreds of kB of rom/flash, and
many tens of kB of RAM, and the radio will still be by far the biggest
thing on the chip.
Even the 48k/10k node from the (very nice) 6lowapp bof presentation is
not up to commercial standards - it's a five year old, expensive,
academic platform - great for it's time, but old. Single-chip nodes
from Jennic, Freescale, etc. have ~200kB ROM/flash + 128kB RAM, a 32bit
processor, and they aren't made in cutting-edge processes yet either.
Life is just going to get better. Let's try to find the smallest
optimized set of *existing* protocols that serve our needs, that run on
the existing new low-cost hardware (not the old workhorses). Let's
invent the absolute minimum of new "optimized" protocols, because it's
not at all clear to me that we are optimizing the right things at this
point. The less we invent, the broader the set of applications and
applications programmers we address.
ksjp
Jonathan Hui wrote:
On Nov 9, 2009, at 5:50 PM, Carsten Bormann wrote:
Again, entirely getting rid of a function is always the best
optimization.
Can we do that for DAD?
The *need* for DAD is the core question for me. As specified within
6lowpan-nd now, IPv6 addresses are maintained using a centralized
protocol. That protocol looks and smells like DHCP - there's
request/response, lease times, relays. The whiteboard may also
administratively assign addresses. So in the end, it's not clear to
me why we would need to *detect* duplicates when we essentially
*avoid* them from the beginning.
I've voiced my comment several times over the past 1+ years and
presented a draft that argues for the use of optimized DHCP in Dublin,
so this is not new from my end. The fact that the current 6lowpan-nd
document has evolved towards using DHCP-like mechanisms is not an
accident. But if what we do is DHCP-like, it would seem to make sense
to utilize existing DHCP infrastructure rather than defining something
new.
--
Jonathan Hui
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