I don't understand what is the primary problem which leads to the steadily falling average ADSL broadband speeds I am experiencing over a long period of time.
When we were originally cabled I took all the fibre services on offer, phone, tv and broadband. But the broadband never worked reliably, often leaving us disconnected for weeks at a time. Booking an NTL engineer usually had one of two outcomes: either he did not turn up, or he came during one of the rare windows when the service was working and then the tests showed no problems. In the end I terminated the NTL broadband service and later also dropped the TV which was playing up in favour of a cheaper and more reliable Sky satellite dish. Since then Virgin has taken over so maybe things would be better now?
Anyway I decided to switch to ADSL for broadband and chose Zen as the provider as they had a good reputation. Tests showed the line capable of 6Mbps out of the 8Mbps maximum available at the time and we got this speed at least some of the time. When the exchange was upgraded to 20Mbps we took that service and got a slight increase in throuput, at least for a while. Then the service went into steady decline over a couple of years until the throughput was rarely exceeding 1Mbps. When I queried this Zen said the problem was due to the line quality and I should complain to BT. BT said there was nothing wrong with line quality and the line was capable of 14Mbps according to their tests. So I terminated the Zen service.
I decided to try O2 who had a good reputation for delivering an uncapped high speed service. When initially connected to their service a couple of years ago, I got speeds between 10 and 12Mbps, so I have no idea why Zen could only deliver 1Mbps through the same line. But it did not last long. The speed reported by the O2 box, both at peak times and off-peak is steadily falling. It dropped to around 8Mbps then to around 5-6Mbps and recently it has held steady at around 4-5Mbps which is what it is doing this morning.
I can live with 4Mbps though the higher speed the line is capable of would be nice, but not if it falls as low as 1Mbps. I went back to BT's line tester and today it is reporting the line as 16Mbps capable. I also checked BT and the Kenilworth exchange is ready for the fibre to the cabinet service. However, if I check our line all I get is a negative and a long list of reasons why we might not be able to have the Infinity service without an indication of the actual reason.
I realise that line capability and actual delivery are two different things. But the line is capable of 12Mbps as it was delivered by O2 for a period of time. So why the downward trend? Using a BT line and a separate ISP means they can blame each other. I am reluctant to drop O2 as they have actually delivered higher speeds reliably over a long period of time where neither NTL nor Zen managed to achieved that. And O2's speed is still usable.