Comments inline:
On Oct 20, 2011, at 12:02 AM, Juliusz Chroboczek wrote:
We have proposed an alternative to WiFi Ad Hoc called WiFi-Opp, which
is more flexible and doesn't require pairing (as in WiFi Direct which
we tested on Galaxy SII).
Very interesting work, although I'm not sure it's an alternative to
ad-hoc.
Well, our goal is to allow "ad hoc" communications w/o WiFi ad hoc
using stock phones (non routed/jailbreaked) and leveraging what is
currently feasible with the Android API, especially the one related to
WiFi.
We don't target geeks that root their phones but the masses.
The tl;dr version: they're running in infrastructure mode, and
randomly
switching between AP and STA. There's a number of heuristics
involved,
but they appear to have refined their algorithms to the point where
they
claim to run a naive flooding protocol at 70% of the performance of
ad-hoc mode, with 20% of the power usage.
Well we do the same with 10% of the power usage and at 90% of the
flooding performances of what WiFi ad hoc would provide you. We use
the same naive flooding approach.
The main difference is that we consider a completely mobile network
(no mesh), i.e., people are switching randomly to AP mode and others
are connecting to these random AP on the go.
Unless I'm missing something, WiFi-Opp doesn't allow quickly scanning
for all the peers in range (which can be done with just a few
multicast
packets in ad-hoc), or communicating with multiple peers in quick suc-
cession (which makes it unsuitable for something like a DHT algorithm,
let alone a mesh network). That's why I'm not so sure about the claim
to being an "alternative" to Ad-Hoc.
True, we can't scan for all peers around as we're using the 802.11b/g
infrastructure features but you might have one of the devices around
you in AP mode through which you can discover all the peers connected
to it.
Since we propose to have nodes randomly switch to AP mode, after some
time you'll see all the peers around you. Actually, we rather think in
terms of content which can be on any peer, not specific peers. That's
probably one big difference between mesh and opportunistic networking.
In the former, you might care about peers, we care about content in
the latter.
A DHT on a completely mobile network is not realistic. There are nice
research papers on DHT for mesh if you want me to provide pointers.
For a quick look at content on peers around you, please have a look
at: http://podnet.ee.ethz.ch/ and related papers. A prototype is
available for windows mobile, symbian and Android.
I was also under the impression that the iPhone supports ad-hoc mode
out
of the box, but the paper claims otherwise.
iPhones can connect to any already existing wifi ad hoc network...but
cannot create one if none exists in the first place.
Franck, could you please clarify two things? First, you claim
a five-fold decrease in power usage w.r.t. ad-hoc, but was that
measured
with WiFi or with Bluetooth? And second, when you speak of
"percentage
of the dissemination performance", what is it exactly you're
measuring?
I clarified this above. Again we use only 10% of what ad hoc would be
using (no Bluetooth). This is simply coming from the sleeping
strategies used for WiFi on Android. You could even make this better
using more advanced sleeping strategies. Ad Hoc is power hungry and
remember how buggy 802.11b was at the beginning (e.g.,
incompatibilities, etc). WiFi Ad Hoc has exactly the same flaws and
will need 1-2 years to get to the same level of maturity.
Thanks for the interesting read,
thanks for your interest and comments. Let me know if something still
needs to be clarified.
--
Franck
-- Juliusz
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