Performance not as expected

I am getting a very different actual download speed compared to what my modem is telling and was hoping someone can help.

I have an ADSL Nation X Modem that is giving me the following stats:

SNR for Download - 16.1
Line Attentuation - 31.4
No CRC errors etc
Data Rate of 5056K

When I test my download speed I typically get around 500K but used to get about 4000K.

My modem is plugged into the master socket and I have changed the filter.

My ISP assures me they haven't throttled my bandwidth.

Short of changing my modem - I am not sure what else to try. Any Ideas?

Which ISP?

which ISP ?

if speedtester.bt.com works cut & paste the results.

If possible could you do a speed test at http://www.thinkbroadband.com/speedtest.html and post a link to the result.

Thanks for the quick response.

Here are the results for the speedtest:

Date 20/05/08 16:07:33
Speed Down 497.07 Kbps ( 0.5 Mbps )
Speed Up 367.05 Kbps ( 0.4 Mbps )
Port 8095
Server speedtest1.adslguide.org.uk

My ISP is Star who use BT Wholesale

Your SNR margin is very high. Perhaps your profile has been knocked down. Could you try the test at http://www.speedtester.bt.com/ which yarwell suggested. This will show your profile.

Hi John,

Here are my results from Speedtester.bt.com

Test1 comprises of Best Effort Test: -provides background information.
IP profile for your line is - 4000 kbps
DSL connection rate: 448 kbps(UP-STREAM) 5056 kbps(DOWN-STREAM)
Actual IP throughput achieved during the test was - 452 kbps

Any idea what can effect the SNR?

the SNR isn't the main issue here, you have 1/8 the throughput of your connection speed and it isn't down to the IP profile.

Your ISP might be congested heavily - know any other users or forums ?

Your exchange might be congested but I would be surprised if it's that bad.

You may have an issue with your RWIN setting - try a tweak tester (link in sig below) in case your RWIN is impeding throughput by being too small.

You are on the correct profile for your sync rate (4544 to 5119 kbps sync gives a profile of 4000 kbps).

The normal target SNR margin is 6dB. This is chosen to give stability over the course of a day when the noise will go up and down. If a line is particularly noisy the target is raised in 3dB steps to a maximum of 15dB. Each rise in target leads to a drop in sync rate.

None of this explains why your download speeds are so low though. Is there any chance that BT are throttling your connection?

It would be worth checking that none of the following applies:

http://www.dslzoneuk.net/socket.php?type=html

Hi Phil,

Thanks for your suggestions. Here are the results for the RWIN Test from Netmonitor- nothing highlighted as a problem.

I am pretty sure my provider doesn't haven't any congestion issues - it is like this at night when their traffic should be at its lowest.

Any other ideas?

Ed

Tweakable settings:
RWIN: -1
Window scaling:
PMTUD: NO
Time stamping:
SACKS:
MSS requested: -1
TTL remaining:

Results of download test:
Data bytes we sent: -1 bytes
Data packets we sent: -1
Retransmitted data packets: -1
Transfer efficiency: 0%
Max packet size you sent (MTU): 39
Max packet size you received (MTU): 39
Data transmit time: -1 seconds
Maximum idle time: -1 milliseconds
Transfer rate: -1 bytes/sec (-0.0 kilobytes/sec)

Ping test:
195.216.14.16 : xmt/rcv/%loss = 10/0/100%


NEW! Suggestions based on these results

This bit is under development, please ignore all the suggestions below for the time being :-)

tick Your RWIN is a multiple of your MSS
tick Few retransmits, looks OK
cross Path MTU discovery is disabled

Your chosen RWIN value will limit your throughput to:
25094 kb/s (3136.7 kB/s) to UK sites (assuming 20ms RTT)
5576 kb/s (697.0 kB/s) to US (East Coast) sites (assuming 90ms RTT)
3346 kb/s (418.2 kB/s) to US (West Coast) sites (assuming 150ms RTT)
2281 kb/s (285.2 kB/s) to Japanese sites (assuming 220ms RTT)