Sudden drop in ADSL speed

Can anybody explain for me what is going wrong here?

My ISP is Demon. I started with their Homeoffice 500 account which was
upgraded last year presumably with the arrival of ADSLmax.

Prior to the upgrade on 19 October 2006 my router reported:
Download speed = 576 kbits/sec
Upload speed = 288 kbits/sec

This was exactly as expected. Performance measuring sites such as
http://www.speedtest.net/ reported average download speeds of about
450kbits/sec - again exactly as expected.

During the few months following the upgrade my router reported:
Download speed = 2880 kbits/sec
Download SNR margin = 12 dB
Download attenuation 60.5 dB
Upload speed = 448 kbits/sec
Taking into account the distance from the exchange these figures are quite
reasonable. The site http://www.speedtest.net/ reported average download
speeds of a little over 1000kbits/sec.

Over the last ten days average download speeds have dropped by at least a
factor of four. The router continues to report the same download and upload
speeds but the site http://www.speedtest.net/ now reports download about
230kbits/sec and curiously upload at 350kbits/sec. The download speed does
vary during the day and often during the evening it will drop to only
100kbits/sec.

Is this something that Demon can fix? Or should I consider changing ISP?

--
Graham J

Graham wrote:
> Can anybody explain for me what is going wrong here?
>
> My ISP is Demon. I started with their Homeoffice 500 account which was
> upgraded last year presumably with the arrival of ADSLmax.
>
> Prior to the upgrade on 19 October 2006 my router reported:
> Download speed = 576 kbits/sec
> Upload speed = 288 kbits/sec
>
> This was exactly as expected. Performance measuring sites such as
> http://www.speedtest.net/ reported average download speeds of about
> 450kbits/sec - again exactly as expected.
>
> During the few months following the upgrade my router reported:
> Download speed = 2880 kbits/sec
> Download SNR margin = 12 dB
> Download attenuation 60.5 dB
> Upload speed = 448 kbits/sec

ISTR Max attempts to train for a SNR of 6dB, so there could be some more
bandwidth that can be squeezed out of the line, but that 12dB is for the
noisiest period, which probably isn't at the point you measured it, so it is
probably about right.

2880/448 is certainly a ADSLMax speed; fixed 2Mbit is 2272/288

> Taking into account the distance from the exchange these figures are quite
> reasonable. The site http://www.speedtest.net/ reported average download
> speeds of a little over 1000kbits/sec.

Speed testers that are on the internet merely measure the slowest point between
them and you; this is not necessarily your speed, but may include problems in
the connection at their ISP, the interconnections between ISP's, Demon problems,
BT ATM issues, oversubscribed exchange backhaul, or problems with your line or
PC. Too many variables.

Are other users on your exchange (which is...?) experiencing similar problems,
regardless of ISP?

Sometimes a disconnect/reconnect cycle will find a different route through BT's
ATM network; there is definitely one path between me and AAISP that seems to
suffer daily degredation with a known pattern, but I'm currently not using it.
http://www.jimhowes.org.uk/linegraph1.gif shows a repeating pattern of packet
loss over two days, ending when I forced a reconnection at 8am)

> Over the last ten days average download speeds have dropped by at least a
> factor of four. The router continues to report the same download and upload
> speeds but the site http://www.speedtest.net/ now reports download about
> 230kbits/sec and curiously upload at 350kbits/sec. The download speed does
> vary during the day and often during the evening it will drop to only
> 100kbits/sec.

Have you checked for any unwelcome network activity on your system that may be
sucking your bandwidth?