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I've seen a team demonstrating an idea of broadcasting an emergency beakon to all the devices connected to a wifi access point without authentication. they claim that they can send upto 27,XXX bytes of data!

I tried to contact them regarding this but didn't get any response.

in the same way i found mobile carriers like att and verizon, instaling updates on the mobile devices of their users to send emergency alerts.

I'd like to try it out as well. I tried searching on google and looking for research papers but found none.

does anyone have any idea about how to achieve this?

Thanks!

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This is rather blurry. Can you describe this system in more detail? What did which team demonstrate? Are there any publications or web pages on this? Was this only to specific devices running specific software? –  Marcel Waldvogel Aug 6 '13 at 7:20

2 Answers 2

The phone system in the US has Wireless Emergency Alerts, but this has nothing to do with wifi and as you point out required a rewrite of software for all existing smartphones.

The wifi management protocol has a beacon frame which can be used in infrastructure mode to announce the name of the wifi network. I suppose you could create a similar emergency beacon, if you are willing to rewrite all the wifi management software in all your devices to transmit and recognize this new frame. It sounds like a lot of work, though.

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so this beacon frame announces the SSID of the network? and i have to write a script that runs on the mobile devices to read this transmission and display it? –  Kiran Vemuri Aug 5 '13 at 17:59
    
I have no idea what you want to do, so I don't know if you can accomplish your task by sending data as SSID names. I am pointing out that if you want to send data to wifi devices that aren't even authenticated, much less associated with an access point, you should probably rethink your solution. You are using a tool for a purpose it was not designed to serve. –  Fred Aug 5 '13 at 18:09
    
I am working on an emergency management system and i wish to send alerts to everyone on campus. I thought sending an alert on everyones mobile device would be effective.. so i thought of this solution. can you suggest me an alternative approach to do this? Thanks. –  Kiran Vemuri Aug 5 '13 at 18:12
    
My suggestion would be to send emergency texts to the phones of people on campus. Put up a webpage, let people register their cell number, and send to those. If you want to send to computers connected to the campus LANs, provide a small program that people can download and run which listens for a broadcast message. –  Fred Aug 5 '13 at 19:10
    
ok. but that would send texts to everyone who's registered right? what if its spring break and they are on a vacation.. i just want the people who are on campus to know.. and what if i want to send the information to the people in a single building on campus? we can use GPS but gps doesn't work well when the device is in a building.. right? –  Kiran Vemuri Aug 5 '13 at 20:54

The easiest and least intrusive is if you have anyone interested in the messages run a specific software that listens to these announcements. So it is your duty to make this software useful enough to them to run it (or have Management mandate its use).

If your campus provides email to all members (and is being used by many), sending out an email to all of them may be good enough. Many will receive it immediately using IMAP IDLE or other push email mechanisms.

A nasty approach which might be able to notify more people in a real emergency might be to redirect their web traffic similar to a captive portal to a page which displays the emergency warning. This works especially well if your WiFi infrastructure can tell you which IP addresses are connected to the access points in a particular building.

Last but not least, a few sirens installed in the building are probably still the fastest, easiest and most cost-effective way of getting people to leave the building in a real emergency (even though many will even then ignore them).

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