On Aug 10, 2007, at 10:47 AM, Kris Pister wrote:
JP - great presentation. I hope that it was well received. I'm
very supportive of everything in that document, with one
exception. There is one assumption that I believe is potentially
fatal to the entire 6lowpan/rsn effort in ietf. On slide 11 you
state "Research has focused on near-optimal solutions to specific
problems", and then in bold "IP is maximizing interoperability, not
aiming at finding a local optimum ;-)". I agree with the second
statement, but the first one is flat out wrong.
Very few people in sensor network research seem to care about near-
optimal solutions. Consider one of the best-received papers
[Kim07] at the recent IPSN conference. Note that the authors are
leaders in the field, this is a respected conference, one of the
better papers, and this is the dissertation work culminating four
years of research on this project. The paper presents the best
academic work to date on reliable multi-hop data collection, MP2P.
The payload goodput in this network was 1.4% of the channel
bandwidth, at 100% radio duty cycle. This is not "near-optimal" in
any sense that I know.
If we start with 1.4%, and then degrade that so that we can
maximize interoperability, we'll be left with something that no one
will use. We have an opportunity to do this right - let's not fall
victim to the Zigbee-esque assumption that all we need to do is
define *something* and adoption will be automatic.
ksjp
[Kim07] Kim, Pakzad, Culler, Demmel, Fenves, Glaser, Turon, "Health
Monitoring of Civil Infrastructures Using Wireless Sensor
Networks", IPSN07.
You're right, Kris, but it's a bit deeper than that. There's a big
debate in the research community right now about layered vs. cross-
layer design, and there are more of the latter than the former. The
protocol briefly mentioned in the paper you cite has a full paper
about it that will be appearing in SenSys. It's clear that a cross-
layer design could lead to higher performance (hence JP's comment
about optimal point solutions), and some reviewers made this point.
But you can't easily compose cross-layer protocols into larger
systems. hence the morass many research systems enter when they try
to incorporate protocols X, Y, and Z together. So the community is
slowly shifting from "how good can we get if we throw out all
layering" and moving towards "what have we learned from that and how
can we apply it to the layers?" That shift is one reason why R2LN's
timing is very auspicious.
The 1.4% is a bit misleading. As 6.2 discusses, the transport
protocol in the paper achieves 94.8% of the layer 3 protocol's
throughput (when considering the 1/3rd effect you get from multihop).
The big inefficiencies are the layer 3 and 2 protocols the particular
implementation builds on, neither of which were optimized for
throughput. It would be great to see how well the e2e transport
protocol works on top of a layer 2 and a layer 3 with this metric in
mind.
Phil
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