Is "unlimited" data really unlimited?

[cubo]

Hello,

I have an S20 Ultra 5g with an unlimited data tariff. I have an extremely slow internet connection at home so my intention was to use the tethering feature to supplement my home internet connection when I wanted to download files (4g for me is approximately 4-5x faster than my home ADSL).

However, on attempting to download a larger file - approx 100gb - it starts well then after around 40gb of data my phone has apparently been kicked off of 4g and onto an "E" signal, which is much slower. On switching off tethering, my connection went back to 4g.

My suspicion is that I have breached some sort of hidden usage cap and the speed is being throttled, but struggling to find information online to confirm this. Is my connection being throttled or traffic managed? 

[MI5]

@cubo 

3.5. Usage of Unlimited Data is subject to our Fair Usage Policy. To help us identify whether you are using your Unlimited Data in accordance with the Fair Usage Policy and these Terms , we may monitor the amount of data you are using. Where you regularly tether to 12 or more devices, have used 650GB of data twice within a 6 month period, or have connected to a device other than an eligible device as stipulated in clause 3.3 of these Terms, then we may investigate your usage further to ascertain whether your Unlimited Data usage is for the permitted use. Where following such investigation we determine or reasonably suspect that your usage is for purposes other than the permitted use then we reserve the right to transfer you to a more suitable plan.

https://www.o2.co.uk/termsandconditions/mobile/unlimited-tariff-terms

[cubo]

Doesn't appear I've gotten anywhere near 650gb.

Clause 3.3 is worded confusingly:
" 3.3 Unlimited UK Data sold on handset or SIMO contracts must only be used in mobile devices that do not require to be plugged in order to work. Any O2 mobile broadband Unlimited UK Data tariffs must only be used with the devices that they are sold with. Where other devices are used that do not comply with these terms, we reserve the right to transfer you to a more suitable plan."

Does that mean you are not allowed to use tethering/mobile hotspot?

[MI5]

@cubo 

Basically it means that O2 can restrict you if they think you are using too much, in anyway, so as not to impact other users.

[madasaf1sh]

@cubo

You can use the hotspot / tethering on the device, what has probably happened is the phone has changed connection to edge due to packet loss on 4G to a more stable network connection.

Personally i would never use a mobile device to download 100Gb files, as the potential for packet loss or corupt files is very high, due to latency inherent on Mobile networks.

[cubo]

Thanks for the reply.

Seems a little disingenuous then, seeing as that ANY device you may be tethered to uses electricity and therefore requires to be "plugged in to be able to work". 

Another case of a company offering "unlimited" data when in reality it's anything but...

[cubo]

Thanks -

It's a game on Steam so connection interruption wont effect or corrupt the file.