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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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I'd give it a week before an open cellphone is considered as antisocial as an open smtp relay.
I don't read ACs: If a post isn't worth so much as a nom de plume to its author then I wont bother either.
How strong is the signal power of a mobile phone?
A base-station is built to receive signals from mobiles far away and is usually equipped
with large antennas and located at a high point.
But the range for mobilephone2mobilephone
communication shouldn't be so long.
A mobile phone signal is very weak.
In the article they are onle talking about the network aspect but not about the "mobile" aspect.
Has anyone an idea about that?
--- censored
This would be also a very useful feature when you have no network connection, the phone would poll at regular times for another phone but only if that one is connected on the network. It seems to be a technological leap forward, though, compared to the situation today.
An easier solution, and also useful, would be the ability to send local messages, without network support. The problem here would be reluctance from the network operators as they would loose revenues.
As we are on the subject, all cell phones should have an "offline" option when you want to read/write messages but are not allowed to or do not want to be connected.
Men are born ignorant, not stupid; they are made stupid by education. Bertrand Russel
The guy who wrote this article probably doesn't know much about how wireless devices actually work.
First of all, for a number of technical reasons, the phones cant actually HEAR each other. Yes, the phone receives and transmits on different frequencies, and it cannot receive on the same frequency it transmits. It would of course be possible to build a phone that could receive on the same freq. it transmits on, but that intorduces a lot of problems that are expensive to solve.
So, unless everybody is willing to pay 10% more for their phones, no amount of software will make this work.
And if the hardware did support this, making it work software wise would be quite a nightmare. I suppose it wouldn't necessarily work worse in emergecies, because it wouldnot work well at the best of times either.
Another thing about these phones is that they are about as far removed from the world of open source as you can imagine - much further than Microsoft. The manufacturers wouldn't be allowed to open up the source even if they wanted to.
Even if every phone had a perfect routing table, you'd still have very severe scaling problems.
Even if almost all of the messages being routed are to phones in the same city, the density of messages at each relay node will be large (total traffic is proportional to the number of nodes talking, and for an even distribution, traffic per node is proportional to the square root of this). A city has a million phones or more. This means that each phone would be routing messages for hundreds or thousands of other phones on a *normal* day. *If* all of the load-balancing in the routing table works perfectly.
Fast forward to Sept. 11th. You have everyone in North America trying to call or message relatives in New York City. The traffic densities as you approach New York would be *HUGE*. Inside the city, you'd have phones trying to handle thousands of messages or *more* at *once*, instead of whenever phone users decided to send. This would melt down the message network in the city and for a little ways around it.
All of this assumes that each phone knows the best route for all messages. In practice, they don't. I'll let someone with more network expertise than I have describe how nasty things get when your phone can only fit a small routing table and you have a constantly-shifting pattern of connections that has to update itself in a decentralized manner (instead of being tracked by a central server that knows where everyone is). Short version: It's not going to be pretty.
In summary, I think that the authours of the article are overlooking a significant problem, especially given that they're proposing this as a way of overcoming system load problems in situations like the Sept. 11th attacks.
First you'd form a piconet. If any of the systems is physically connected to (internet | base station | something else), relay there, else form/connect next device on a (same | different) piconet (the next device might have different piconets available). When the working relay is found, send back a message, targetting the original device. Relay it randomly and add a node to the route table the message contains. The original sender can deduce a short path (it's not necessarily the shortest!) just by looking at the message that arrives first/has the shortest route.
At this point, it should be possible to send small text messages with some efficiency.
It's also possible for other devices that happen to recieve a route recovery message to use the some of the readymade routes (so that everyone doesn't need to do this slow procedure).
The total amount of transferrable payload *per device* should probably be limited to something like 2kB, if this is to be used as an emergency network, to insure everyone can transmit their messages.
Any ideas/corrections from those "in the know", especially bluetooth people here?
Disclaimer: I'm not a bluetooth specialist... In fact I don't know much at all about it! :)
Silly people... Ham Radio has been doing packet radio for 19 years now with AX.25. It works great, has TCP/IP overlay, is fault tolerant, and it quite inexpensive... with Linux gateways to internet. Again... nothing new here - just applying the same technology to cellular that has been on other "OPEN" RF links for nearly two decades...
One thing about ham radio -- you *can* run it on backup power....
Actually, I wonder... is there a subculture out there of people using hacked cellphones for legitimate, i.e. hobbyist, purposes? I don't mean cell phreakers or people using stolen service, I mean people doing precisely this p2p sort of thing, completely off the nets (or even using their own shadow nets). I can't think it would be that hard to do -- the only problems would be a) modifying the firmware and b) hooking your cell-frequency ham radio tower up to a PBX to connect to the rest of the phone net...
/Brian
Are these the iDen phones? (Mike network?)
If so, I think you misunderstand what was happening. They were basically using a digital signalling technology to make it appear like a p2p network. Basically you were subscribed to a calling group, or had someone else's number programmed already, and whenever you pressed the Push-To-Talk button it just called up the receivers and they automatically answered - all in less than a second - and put it on the speakerphone.
sufficiently advanced technology == magic, etc.
If you're a ham radio op. If you have a loose network of hams with dual band handhelds, you can cross-band and relay a message a long distance using other people's handhelds. Of course, this all requires the cooperation of the user. Let's look, perhaps, at how this could have helped in the NYC tragedy:
Op with a 5 watt handheld has set up a small communication base near ground zero. The op can sync up with another op a few miles away and relay help and welfare information. Ground zero does not have power. The second op does not have power. The second op is able to relay the message to a ham with power who can relay the info on 20 meter to the other side of the country. With minimal amounts of planning and just a few hams, a system is devised that permits message relaying all over the country, even though the phone system is jammed and power is down for miles. Anyone with a decent scanner can pick up the signal on 20 meters and hear a nice formatted report of people who are OK.
There is no reasonable defense against an idiot with an agenda
:wq
10 years ago or so, before Cell phone's exist as they do nowadays, Motorola had a 900mhz system that was like cell phones but not the same in all aspects.
Anyways, the phones could be tweaked to the ham bands with a little bit of work. The ones I saw were only land-line linked through a standard auto patch and they were mainly used to talk to other hams with modified phones.
Pete
What the article describes is the old military concept of "mobile mesh network". Highly survivable solutions are a must in a combat environment, but their their characteristics make them completely unmarketable. In our specific example, the reasons are as follow :
Full-mesh wireless networks like JTIDS are inherently inefficient because one cannot make
range (timing) and Doppler corrections at the transmitters, and because there is no frequency
reuse. With a repeater-based architecture, all transmitters can adjust timing and frequency to
correct for their range from the repeater and for relative velocity. In a full-mesh network, all of
the other nodes are potential receivers, but one can make range and Doppler corrections for only
one of them. With multiple repeaters (base stations), two repeaters that are not close to one
another can use the same frequencies without interference; such frequency reuse enables large
increases in system capacity over full-mesh and single-repeater architectures. Decreasing cell size in order to increase frequency reuse reduces the survivability of the network.
A closely related concept is that of the self-organizing hierarchical network. These networks are similar to the homogeneous mobile mesh networks, except that nodes organize themselves into clusters and by some means "elect" a cluster head (see, for example, Alwan et. al, 1996). The cluster head is responsible for keeping track of the membership of the cluster and the locations of nearby cluster heads, and for performing routing, switching, and trunking functions. However, since any node must be able to function as the cluster head, cost and battery life are likely to be problematic. Remember that mobile devices are highly contrained.
The problem with military stuff is that it is grossly overengineered from a civilian point of view. We all would like to carry cutting edge radio hardware with us and be ready for all kinds of emergencies, but there is a price to pay and the civilian market won't bear it, preferring to take long term risks and to get more features and more performance in the short term. If survivability was foremost, everyone would be backing up their data. Field experience shows that it is not he case.
Sources :
http://www.google.com/search?q=cache:3fDYY36opQQ:w ww.rand.org/publications/MR/MR960/MR960.chap3.pdf+ tactical+network+relay+node++survivability
http://dss.ll.mit.edu/dss.web/98F-SIW-143.html