Tag Archives: SSID

Opting-out of Google Location Server

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In September Google announced their intention to comply with requests from European data protection authorities and offer a method for opting-out of their Google Location Server (GLS).

Peter Fleischer (Google’s Global Privacy Counsel) has today published an update on the European Public Policy Blog and Google have added specific opt-out details on their Maps Help page.

What is GLS? It’s a location service that most Android smart phones use to request your current location. Your smart phone could simply use satellite positioning (GPS) to accurately pin-point your location, but GPS consumes battery and generally only works outside.

Instead of using GPS your smart phone attempts to discover your location by scanning for nearby WiFi access points. It gathers the relative signal strengths, network names and unique network addresses and sends the details to the Google Location Server (GLS) for processing.

The GLS checks its database of WiFi access points and returns an estimate of your location. If your local WiFi access points are known and already in the GLS then it will return a fairly accurate location, almost on a par with GPS, for a fraction of the power.

Google built their WiFi location database while collecting data for Google StreetView and it is constantly updated and augmented by smart phone crowdsourcing. The manner in which Google collected this data has been controversial and Google have been investigated for breaches of interception laws. As a result Google has been forced to offer this opt-out scheme to appease regulators.

So what do you need to do to ensure that your own WiFi access point is not included in the Google Location Server database?

Simply append “_nomap” to the SSID of your WiFi network and Google will remove it from their database the next time a device sends information to the GLS.

It’s undoubtedly an inconvenience to change your WiFi network name and re-associate all your wireless devices, but if this scheme is adopted by all the mapping services (Microsoft, Apple, Skyhook) then it could well be worth it.

BT fix Openzone roaming

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In July 2008 O2 announced a deal with BT to provide access to over 3,000 BT Openzone premier WiFi hotspots for all their iPhone customers.

There was however a technical spanner in the works, which has prevailed in ruining this bonus ever since. The name of this ‘spanner’ is BT FON.

FON is a network of community hotspots, which in the UK is mostly made up of BT Total Broadband customers. As a BT customer you can opt-in to sharing your broadband bandwidth with other FON members. In return you have access to any BT FON community hotspot that you come across.

It’s actually quite a neat idea, but the launch of this service introduced a big problem for iPhone customers trying to use the BT Openzone premier hotspots.

For reasons best known to themselves, when BT set up a BT FON community hotspot they also make it act like a BT Openzone hotspot. This is fine if you’re a BT FON member as you can roam onto either of these networks, but if you’re a subscriber of BT Openzone through a partner like O2 then you only have access to the BT Openzone premier hotspots.

Most smartphones remember known WiFi networks and will automatically associate with them when they are in range. The only way they have of differentiating between networks is the network name – or SSID.

If you save the “BT Openzone” SSID on your smartphone then it will attempt to use a WiFi hotspot that broadcasts that name whenever it’s in range. This allows the device to seamlessly move between WiFi access points and cellular data without having to ask you each time.

The problem for O2 customers is that when have registered with BT Openzone and saved it as a known network, your smartphone will blindly associate with any hotspot which claims to be “BT Openzone”. This includes the BT FON hotspots for which you don’t have access!

When this happens your smartphone effectively goes offline and apps which rely on a data connection stop working until you move out of range. The only remedy for this is to remove BT Openzone from the known networks list, which is an inconvenience and negates the benefits of a BT Openzone subscription.

Now finally it seems that BT are addressing the problem. They are hastily updating residential home hubs and changing the broadcast SSID from “BT Openzone” to “BT Openzone-H”.

Thank you BT. It’s only taken you 4 years to sort this mess out.

Apple AirPort trusted networks list

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I was tearing my hair out trying to understand why my MacBook repeatedly joined a WiFi network, despite my removing the SSID from the preferred networks list and deleting the AirPort network password from the System Keychain. I was attempting to force my MacBook to only associate with the 5GHz version of a WiFi network (on an Airport Extreme Base Station), but no matter what I did I would find that the MacBook occasionally reverted to associating with the original 2GHz SSID again.

The mystery was solved with the discovery that as well as the WiFi Preferred Networks list, there is a hidden trusted networks list buried deep within Mac OS X. Even if you remove a network SSID from the visible lists, your MacBook can still silently associate with previously saved networks.

Mac OS X retains WiFi network information and authentication credentials in the com.apple.airport.preferences.plist file which is located in the /Library/Preferences/SystemConfiguration folder.

To remove WiFi networks, either delete the individual networks from the KnownNetworks key using Property List Editor, or delete the file altogether and allow AirPort to rebuild it. It’s probably a good idea to turn AirPort off before editing the file.

There is an old Apple knowledge base article – AirPort: How to reset the trusted networks list – which also describes this.