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Peer-to-Peer Cellular
Phos writes: "A cool article over at the O'Reilly Network outlines a possible solution to cellular network outages in the event of an emergency. A P2P SMS technique where individual handsets act as autonomous SMS relays."
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This article examines the task of creating a wireless communication system that can survive a catastrophic failure, and still provide basic communication services to its users.
It's called Amateur or 'ham' radio - every year they have an event called 'field day' which is an exercise in taking your gear out and operating on generators, etc. 2 Meter handy talkies can work thru a repeater or direct simplex (peer-to-peer) if the repeater is down.
I'll never forget listening to a ham during hurricane floyd, w/o power, operating on emergency backup power, 80 meter band, crouched in his garage on the NCarolina cost reporting the fierce winds in the night.
try { do() || do_not(); } catch (JediException err) { yoda(err); }
It is called a Mobile Ad-hoc Network (manet) and the IETF has a working group which has come up with some protocols and such.
. ht ml
http://www.ietf.org/html.charters/manet-charter
Interested readers should probably read A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing Protocols to find out why this is difficult.
According to the article, phones would have to exchange and update their routing information all the time, even while everything was working normally (because by definition a phone can not know if a neighboring base station that's just out of reach is still working or not). Every phone would continuously keep broadcasting a list of every other phone and base station in it's reach.
This overhead alone (just to update the routing tables) would consume a big chunk of the bandwith all the time. Since a base station dropout or overload is an exception (hopefully), a dynamic on-demand routing protocol would make much more sense in this case.
Idempotent operation: Like MS software, wether you run it once or often, that doesn't make it any better.
I think I recall this ....
Typical cellphones are a few hundred milliWatts.
A tower can punch out power (in some cases) up to 60 Watts or more, though it doesn't usually.
At least that was how it worked for cell data systems such as CDPD. Cellphones are probably analogous. I think when they try to either acquire a channel or when they are broadcasting, they can amp the power up (I'm not sure quite at what starting level they use) up to 200 or 300 mW max. If you have one of the in-car systems, you can go up to 2 or 3 W. (Considerable increase in range, and the big ass antennae helps receiving fainter signals). Towers can pretty much always reach a phone that can reach them. Usually it is the phones returning signal that drops below the noise threshold rather than the signal from the tower.
FYI... (from memories a couple or four years old).
Tomb
-- Mal: "Well they tell you: never hit a man with a closed fist. But it is, on occasion, hilarious."
No, it doesn't. Rather than try to explain why not, I suggest you read Ad Hoc Networking by Charles Perkins (editor) or the papers and references from the IETF MANET working group, or some of the stuff from CMU or Cornell. In short, an end-node usually only needs to know about its immediate neighbors, plus a modest amount of information regarding location (either physical or abstract).
Absolutely not.
Wrong again. Both end-to-end and in-network retransmission and acknowledgement can be used to prevent such loss even in the face of multiple failures. That's just basic networking, not even specific to mobile networks.
The problems you mention are real, but don't assume that solutions do not or cannot exist just because you weren't able to see them after a few minutes' worth of independent thought. Some pretty bright people have been working on them for twenty years or more, not without success, and before you assume "it won't work" you owe it to yourself to find out whether you've been proven wrong already.
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