Sync speed, IP Profile and actual measured speed discrepancy

Hi all, (this is my first post so please be gentle with me)

I've got an ADSL2+ connection and live only 300m from the exchange (as the crow flies) so I expect to get a decent speed.

My modem syncs at 20898kbps and my IP profile is 19.5Mbps (according to BTW diagnostics) but the actual measured speed (on BTW speed test) is only 11Mbps. I have a Netgear DG834 modem which indicates line attenuation = 13db and Noise margin = 3db.

I've had ADSL2+ for a couple of months now so expect it to have settled down, but the achieved speed has never exceeded 11Mbps.

My understanding is that the achieved speed should be somewhere close to the IP profile speed as the IP profile is the throttling mechanism to prevent the local-loop bottleneck from causing buffer overflows and packet loss. Am I right or can anyone correct my understanding here?

I've talked to my ISP, Freeola (Entanet), and but they say the achieved speed is within acceptable limits and can't be investigated. One suspicion I have is that my ISP is capping my speed at 11Mbps, if so should I consider changing ISP? Obviously I'd like to get the highest speed possible.

Thanks for any feedback on this.

Edited by deleted (Wed 19-Sep-12 11:16:40)

If the BT speed tester indicates 11Mbps for throughput then it is very unlikely that the ISP is capping your speed.

I assume that you are using a wired ethernet connection between the router and the computer and that you have perhaps eliminated any possible negative effects of telephone extension wiring by plugging the router into the master NTE5 (?) test socket. Also have you tried different filters and adsl rj11 leads at the test socket?

While unlikely, it can depend on the ISP and how they interconnect to the WBC network, as with some the speedtest is totally on BT Wholesale network, for some the ISP does end up influencing.

The router stats suggest that probably not a wiring issue, and more to do with a throughput issue on the PC or the backhaul network.

I presume the speedtest was done when using Ethernet, as wireless can often be the bottleneck in the home.

Thanks for your reply 4M2.

I have a 16-port Netgear Pro Gigabit switch connected between the modem and the PC that's measuring the speed all wired up with CAT5e.

The modem is connected directly to the BT master socket with a 1m cable. I've not disconnected the ring cable though, I've read that this can help SNR.

Is it normal for there to be such a large difference between the IP profile and the actual measured speed? My understanding is that the IP Profile is based on the sync speed and the sync speed is based on the measured parameters such as SNR and error rates over time. So ultimately the IP profile is a measure of your local-loop's potential capacity. If I had a noise problem on the line, surely the sync speed and hence IP profile would be lower.

As such, I don't see why the measured throughput is only just over half of the IP profile speed.

you could find a large file and download it, looking at the throughput on your connection while it happens. Do this at 7am and see if it caps out at a particular value. http://www.thinkbroadband.com/download/

What's your OS ? The MTU / RWIN settings can limit throughput, esp with Win XP or earlier - check on a tweak testing site.

Even better download two files at once, to help saturate the link then monitor the stats on the switch

In reply to a post by Decepticon:

Is it normal for there to be such a large difference between the IP profile and the actual measured speed? My understanding is that the IP Profile is based on the sync speed and the sync speed is based on the measured parameters such as SNR and error rates over time. So ultimately the IP profile is a measure of your local-loop's potential capacity. If I had a noise problem on the line, surely the sync speed and hence IP profile would be lower.

As such, I don't see why the measured throughput is only just over half of the IP profile speed.

Your line is "very good" (see: http://www.coolwebhome.co.uk/calc/calculator.php ) and there are certainly no problems with SNRM, sync, attenuation and IP profile so there's absolutely no need to be concerned about those

But something is affecting your throughput and I think we have to explore all the possible causes...

In reply to a post by MrSaffron:

Even better download two files at once, to help saturate the link ...

That's interesting because if I do a TBB speed test at the same time that my AV app (KIS 2012) is downloading an update I only loose ~200Kbps, i.e. ~11000Kbps down to ~10800Kbps on the result.

an AV app updating isn't always the same as a download - a lot of updates trickle along rather than downloading full blast.

In reply to a post by yarwell:

an AV app updating isn't always the same as a download - a lot of updates trickle along rather than downloading full blast.

Especially Kaspersky updates!!!

Thanks for the info yarwell.