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Whereas the Vodafone Broadband app consistently and continuously states that my speed has been 40.0Mb/s for the last two months, an independent check using the SpeedTest app shows that my connection has never gotten above 23.2Mb/s which is well under the guarantee limit.
Think that Vodafone is trying to dupe us with its static speed test
This may be a difference between the line (sync) speed which may well be 40mbps and the throughput which in your tests in measuring 23mbps. The line speed will be the speed between the router and the exchange while the throughput is the speed between the speedtest app and the speedtest server.
Is the speedtest results always the same? Do they ever get near 40mbps?
So you're basically saying that the Vodafone router itself is sinking 20Mbps?
Might try a third party router to see if that will improve the service.
Typical Vodafone, Guarantee the speed to their router but not that which is available from their router to the user!!!!
So if I use the Ookla speed test site, when I try different servers I get different speeds! The speed you'll see it that if the tightest bottleneck en route. So you may just want to try connecting to a number of different speedtest servers.
I'm not saying that your connection isn't slower than it should be, just that you may need to check your speeds on a few more servers!
Getting your own equipment is unlikely to give you a near 50% speed improvement - there may be a little, but no where near that much, and if you are currently getting the redemption because your sync speed is not meeting the minimum, you'll lose that as the phone app won't work without the supplied router!