How Three knows you are tethering

If you have an iPad or other tablet without a SIM slot, the only way to get an internet connection is via Wi-Fi. That's fine when you're at home or near another Wi-Fi hotspot, but when you're on the move the only option is to connect to a hotspot generated by your smartphone. This is called tethering, and here we explain how mobile operators know you're doing it and how to avoid tethering blocks. Also see: Best MiFi 2016.

Not all smartphones let you create a 'personal hotspot' and share your 3G or 4G connection, but many do. However, not all 3G and 4G tariffs allow tethering, so you could end up with a warning or even being cut off if you break the rules.

It doesn't any more, but Three used to limit tethering only to certain mobile tariffs. If you weren't on one of these and you tethered anyway, you'd likely get a message telling you to cease and desist, or face your connection being suspended.

So how does Three - and other operators know that you're sharing your mobile data connection with another device?

We put the question to Three, which not too surprisingly declined to answer. However, if you think about it logically, it should be fairly simple to detect tethering. Every device with a network connection (including Wi-Fi) has a unique hardware identifier called a MAC address. Assuming that the operator can trace the final destination of the data packets, it should be able to determine that the final MAC doesn't match your phone's.

There are lots of other ways, too, from web browser identifiers, software, firmware revisions and more. For example, if you were tethering a full-blown Windows tablet which requested a software update, this would raise a red flag, since it's not a mobile operating system.

Similarly, the type of data could be used. If you start using bit torrent to download files, you're probably tethering.

How to bypass tethering blocks

If you were hoping for a step-by-step guide to getting around a tethering ban, you're about to be disappointed. Most operators allow tethering these days. Both Three and Giffgaff - companies which used to restrict or ban it - now allow tethering up to your monthly data allowance.

This is what we've always thought was the fairest way to deal with it: you've paid for the data, so you should be able to use it for whatever you like on any device.

So, if you're on tariff which doesn't allow tethering then it's simplest to switch to one that does. There are some excellent pay monthly deals around, so you'll probably save money to boot.

 See also: How to use your phone as a Wi-Fi hotspot - the complete guide to tethering