I read Ian Pennell's article on ADSL speeds where the "BBmax ADSL tester" calculated his download speeds at 500kb. Therefore his true connection speed is approximately 512kb and not the 2mb he may be expecting. It is difficult to explain, but here is my interpretation of how this happens?
An ADSL link to the internet is more than likely shared at the exchange with other ADSL users, this is called a "contended service" and offered by most ISP's. The "Contention" could be "20 to 1" or "50 to 1", meaning that you are competing with either "19" or "49" other adsl connections. The more demands on the service, the less bandwidth available for all users of the "contended service".
How it works:- Your data and that of other ADSL customers in the "contended service" are transferred to the "BT ATM" network using backhaul links from the exchange. The BT backhaul links as standard are approx 4Mb/s or 4094kb/s, but this is dependant upon the exchange. Up to 400 customers can share a single 4096kb/s backhaul. Saturation point is, I suppose technically possible, this is where you would see bandwidth decrease so much that the service would be unusable. As your ISP knows this already I would think that the "Contended Service" is more than likely shared between business users and private users, as they are less likely to be using bandwidth at the same time.
The MWM:- I'm not sure why your link would drop off the MWM, but "Mesh Networks" normally have the ability to use alternative routes which offers redundancy and guarantees the service level. Having just spoken with my partner for advice I am reliably informed that the MWM has been upgraded over the past few months and this may have corrected the connection issue for you. If you are still a part of the MWM then you may wish to retest it, as this will offer you up to 6mb/s.
Kind Regards
Tania Smith