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Topic: Skyhook, wifi, magic

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Old 04-07-2011, 07:18 PM
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Skyhook, wifi, magic

Hi

I have scoured these posts for a little enlightenment on the mechanics of the brilliant Skyhook scheme - the way I understand it working and what I observe leaves me somewhat perplexed.

What I think is going on:

In the wifi end of things (there is also cell and GPS in their new expanded system) Skyhook maintains a gigantic d/b that relates wireless radio mac address to a location.

The majority of this d/b was and is being fed by survey similar to the way Google does their street view gathering; guys driving around collecting wifi signatures by location. They also welcome manual additions to the d/b; use their form on the web to enter your wifi's wireless radio mac address and lat/lon location and your wifi will eventually be part of it all.

This d/b is made available to applications by real time IP query thus:

The application (Google maps, Google earth, some astronomy program that needs location, etc) queries Skyhook's server(s) with the current wifi "cloud"
signature (could be one or several 'seen' mac addresses) and the Skyhook server returns location info back to the application which then 'knows' where it is (current location) For now we're just considering the wifi part; a big part of the SkyHook info includes cell tower triangulation, and GPS fixes.

However: I have an Ipod touch 4 which as we all know has no GPS and no cell awareness so wifi is it. I live in an area that is not surveyed by SkyHook
and presumably none of the wifi routers in the few homes around here have been manually added to the d/b. (I live in a western mass hilltown pop. 800)

Yet I can drive at a respectable clip and notice that my location enabled application actually does update my location. I am flumoxed (amazed) at whats happening. These wifi signals my ipod is sensing (I'm whizzing by 45 mph) are somehow registered with Skyhook AND the wifi is unprotected in the first place AND the app has time to IP a query to SkyHooks d/b AND SkyHook responds with location data before I lose connection.

wow.

Just to confuse me further my neighbor has a dsl inet connection just like mine; when I am at his house (my ipod connected to his net) location services works; at my house it does not work. This could be a firewall issue perhaps, but he has definately not registered his wifi with SkyHook and yet it works there.....

Anybody out there work for SkyHook?

Peace,

Malcolm
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Old 04-07-2011, 09:00 PM
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Well first, Apple stopped using Skyhook awhile back in favor of something similar, which I think may be their own acquisition from a few years back. If I'm not mistaken, the change happened along with the change from iOS 3 to 4, so if you had an older Touch on iOS 3 it would still be using Skyhook.

As far as the nuts and bolts of how Skyhook or Apple's system works with wi-fi only, the Touch would have to see an open network in order to ascertain its MAC address to decode its location. A hidden network can't be used, unless somehow there is still enough info broadcast to determine the router's MAC (I doubt it though).

As to why your house is not working, you must not be entered into Apple's database. With Skyhook you can submit your MAC and location, but with Apple there is no such utility that I know of. But the good thing is, when you're home you know where you are
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Old 04-08-2011, 07:58 AM
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It's unclear how Apple gets location information into its database, but I wouldn't be surprised if all GPS-equipped IOS devices are surveying open Wi-FI access points and reporting coordinates as normal users move around.

Note that a Wi-Fi access point doesn't have to be unprotected to be used for location positioning. Protected Wi-Fi access points still provide enough information to be used for triangulation -- you just can't actually connect to them or get onto the Internet this way. "Closed" (or hidden) Wi-FI access points (those that don't broadcast their SSID) can also still be theoretically used, although these are trickier to locate and I suspect that iOS devices probably aren't jumping through the extra hoops required, not to mention the potential privacy concerns with regard to doing so.

Note that the Location Services APIs are an OS-level thing, so the apps themselves -- even things like the built-in Maps app -- are just asking iOS for a location fix. The OS provides the best location fix that it can and the app isn't necessarily informed as to whether the fix is based on WI-Fi, cellular triangulation or GPS, although the accuracy of the coordinates and the presence of an altitude value can be used to determine if a GPS fix is in fact available.



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Old 04-08-2011, 11:27 AM
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OK so if Apple is now using something other than Skyhook that explains a lot. (I was basing all my theories on Skyhooks methodology)

Could it be that Apple systems connected to wifi routers somehow instruct those routers to broadcast as part of their 100 ms 'here I am' burst a packet with location info encoded? This is how it seems to be happening because as I posted earlier I just cannot believe there is time for a query (IP) to have been generated and responded to. (ipod 4 no cell for IP; whipping past wifi warm spots)

I did return to one wifi that updated my location and sure enough it was non protected.

I would ask Apple but they keep stuff like this pretty close to the vest.

I'm gonna look into the wifi standard to see if there is provision in the packet protocol for info like position etc.

Then I gotta get a life.

M
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Old 04-08-2011, 11:40 AM
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Well, if the location database is cached on the device itself that would explain how it can do lookups even when you're out of Wi-Fi coverage. While it's unlikely that the device stores the entire worldwide database, it would be fairly easy to download and cache a list of all of the nearby Wi-Fi hotspots. Open Wi-Fi access points are broadcasting their SSID and MAC addresses and it takes fractions of a second for the iOS device to read this information.

As I undersand it, the methodology is very similar to what Skyhook is doing. Apple brought it in-house primarily because like most things they don't want to rely on third-parties that may or may not continue cooperating. Rumour has it that Apple has been working on its own mapping solutions for the same reasons.

I'm not aware of anything in the Wi-Fi protocol itself that encodes location data -- that's handled at a higher level, but even if such a feature existed, it wouldn't be implemented on 99% of the Wi-Fi routers out there.



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