In reply to a post by Decepticon:

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?

It's nowt to with throttling etc as you say. The diff between throughput and Sync speed is accounted for by the protocol overheads (ADSL & TCP/IP) of the transmission, of which the IP Profile accounts just for the ADSL overheads.

As a rule of thumb:
IP Profile = 88.2% of Sync
Throughput = about 83.5 % of Sync

So you should be downloading at about 17.5 Meg.

That you are not is likely to be down to congestion somewhere in the network.

Would the OP have suffered with the effects of congestion continuously for a couple of months though?

In reply to a post by Decepticon:

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.

Your noise margin is bare minimum (3db) and I have seen dropping connections and low throughput at these levels. This may be causing your throughput problem as its possible that there are bursts of noise or other forms of REIN/SHINE on occassion that might interfere since there's very little margin for error with a 3db noise margin.

Generally 3db is not even selectable to put someone on to, the minimum is 6db.

EDIT: It could even just be an over-subscribed street cabinet.

Edited by deleted (Wed 19-Sep-12 15:37:43)

On lines that BT Wholesale determine to be stable they lower their standard 6dB target to 3dB now. So it is not a total indicator of a fault/problem

Also an over subscribed street cabinet would not affect ADSL throughput, as the ADSL signal is 1:1 contention until it reaches the MSAN at the exchange.

Generally 3db is not even selectable to put someone on to

3 dB profiles have been available for years, but only recently widely used. Quick gain to meet the 2M USC perhaps.

In reply to a post by MrSaffron:

On lines that BT Wholesale determine to be stable they lower their standard 6dB target to 3dB now. So it is not a total indicator of a fault/problem

Also an over subscribed street cabinet would not affect ADSL throughput, as the ADSL signal is 1:1 contention until it reaches the MSAN at the exchange.

Strange considering I've seen this affect the noise margins unpredictably in the past when sending out engineers, maybe I didn't get the full side of the story.

Is there any reason one might not be able to select a 3db noise margin on upload / download when performing SNR resets from a CP point of view?

Cannot comment on what your provider provided to you in your support interface.

A full cabinet can increase cross-talk, but we are looking at a line with almost full sync and no complaints of poor noise margin, rather than appears to be a backhaul throughput issue.

Remember the DSL segment is perhaps 1% of the network between home and internet. Yes it does account for a lot of issues, but in this case I do not believe it is the issue. The trick to forum support is jumping outside the standard script.

In reply to a post by MrSaffron:

Cannot comment on what your provider provided to you in your support interface.

A full cabinet can increase cross-talk, but we are looking at a line with almost full sync and no complaints of poor noise margin, rather than appears to be a backhaul throughput issue.

Remember the DSL segment is perhaps 1% of the network between home and internet. Yes it does account for a lot of issues, but in this case I do not believe it is the issue. The trick to forum support is jumping outside the standard script.

Ok, well the support software we had only allowed a range between 6db and 15db to be selectable so my information may now be out of date.

There is not a great deal of investigatory evidence so far:

The only thing I picked up is that his ISP said there can be no investigation, I would question whether he is using a popular speed test site as opposed to the BT performance tester, as those are recorded and can be seen by support staff, typically a test on that resulting in more than a 30% loss would result in a fail which can be investigated.

What I do know is that if its a congestion issue thats going to be beyond our scope of support here on a forum and rests firmly in the hands of the ISP and BT.

In reply to a post by Kaytfoh:

I would question whether he is using a popular speed test site as opposed to the BT performance tester

Well, OP did state "but the actual measured speed (on BTW speed test) is only 11Mbps" so we can only go by what he says and not speculate he is telling porkies.

You do seem very last century on your info, viz, 3 dB NMs, NTE5s, MTUs ...

In reply to a post by XRaySpeX:

In reply to a post by Kaytfoh:

I would question whether he is using a popular speed test site as opposed to the BT performance tester

Well, OP did state "but the actual measured speed (on BTW speed test) is only 11Mbps" so we can only go by what he says and not speculate he is telling porkies.

You do seem very last century on your info, viz, 3 dB NMs, NTE5s, MTUs ...

Then he basically needs to push the support staff more because that would show as a fail on any BT recorded speed test, they are not doing all that they can.

Noise margins still play a part in speed and in particular those with high amounts of errors and HEC errors on lines at 3db. Some people still don't even have NTE5s, and the information for MTU was correct as with IPStream, maybe that has changed with WBC but not really had the need to re-do that test on someone with WBC.

So rather than just say my information is wrong provide me with evidence or reasoning on how my answers are incorrect and what they should actually be rather than just say its out of date. Then we can all learn something.