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Line Threshold Speeds - "Acceptable Range"

Community Veteran
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Registered: ‎14-07-2009

Line Threshold Speeds - "Acceptable Range"

Quote from: chrispurvey
The thresholds are not secret, it would depend on what your line is capable of. Each threshold will be different, this applies for the download and upload speed.
It is normally taken from the Fault Threshold Rate, loop loss and line length and it will also depend on the quality of the line.
You should be getting speeds around what your line <a href="http://www.dslchecker.bt.com/adsl/adslchecker.welcome">estimates</a> are.
The BT speed test would be also give an idea of the acceptable range as jelv states.


Not wanting to hijack another thread I have started a new one.
Last week I went to visit a client with very poor broadband.  If I put his number into the BT Broadband Availabilty checker it says:
Quote
Your exchange is ADSL enabled, and our initial test on your line indicates that your line should be able to have an ADSL broadband service that provides a fixed line speed up to 1Mbps. However due to the length of your line the 1Mbps service may require an engineer visit who will, where possible, supply the broadband service.
Our test also indicates that your line currently supports an estimated ADSL Max broadband line speed of 1.5Mbps; typically the line speed would range between 500Kbps and 2.5Mbps.
Our test also indicates that your line currently supports an estimated ADSL2+ broadband line speed of 2Mbps; typically the line speed would range between 1Mbps and 3.5Mbps.
The actual stable line speed supportable will be determined during the first 10 days of use. This speed may change over time, to ensure line stability is maintained.

He's a BT client and he actually gets 750kbps sync with about 63dB of downstream attenuation.  He has no master socket and all his telephone extensions are BT branded.  I spent at least two hour talking to BT Tech Support on his behalf and the conversation ended when BT concluded his speed was "within the acceptable range" and so they were not prepared to do anything about it.
So this "acceptable range" is a bit of a sore point with me at the moment.  If what I was told is true then I could have saved myself a lot of wasted time if I could have found it out for myself.  But I still don't know quite how.
I don't trust the peripheral information around the BT speedtest because that tends to adapt to what it finds.  Thus if I run a test and get 500 kbps it is likely to tell me the best I can do is around 1000 kbps even if all I have to do to get 4000 kbps is to connect to the test socket.  Obviously the core information of actual measured speeds and IP profile is correct, it's the estimates that seem to go wrong.       
16 REPLIES
James
Grafter
Posts: 21,036
Registered: ‎04-04-2007

Re: Line Threshold Speeds - "Acceptable Range"

You're referring to the Fault Threshold Rate which we see when running line tests.
There is no way for one of our customers to know this without asking us.
Community Veteran
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Re: Line Threshold Speeds - "Acceptable Range"

Quote from: Jameseh
You're referring to the Fault Threshold Rate...

I'll have to take your word for that, James.  So what useful information does a line test tell you that I cannot get from my router?
James
Grafter
Posts: 21,036
Registered: ‎04-04-2007

Re: Line Threshold Speeds - "Acceptable Range"

The FTR is set during the first 10 days. It is 70% of the MSR (Maximum Stable Rate) which is the lowest speed at which you sync during the training period.
Syncing at beneath the FTR gives us the ability to raise an EPP (End user Poor Performance) fault to BT Wholesale.
Of course your line stats are still useful for diagnosing problems as well as seeing if your speeds are below those given in the BT availability checker.
Community Veteran
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Registered: ‎08-01-2008

Re: Line Threshold Speeds - "Acceptable Range"

Isn't the 'Acceptable range' the same as is shown in the BT (Diagnostic) Speedtester?
Quote
For your connection, the acceptable range of speeds is...

If http://speedtester.bt.com or http://www.speedtester.bt.com don't work, try http://speedtest.btwholesale.com/ and select 'Further Diagnostics' at the end of the first test.
Call me 'w23'
At any given moment in the universe many things happen. Coincidence is a matter of how close these events are in space, time and relationship.
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Community Veteran
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Registered: ‎15-06-2007

Re: Line Threshold Speeds - "Acceptable Range"

The acceptable range of speeds given in the BT speedtester are related to the IP profile so only check that something else isn't throttling it such as Exchange Congestion
Community Veteran
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Re: Line Threshold Speeds - "Acceptable Range"

So, the lowest 'acceptable speed' on the BT diagnostics tester has nothing to do with FTR at all?
Seems a bit daft.
Call me 'w23'
At any given moment in the universe many things happen. Coincidence is a matter of how close these events are in space, time and relationship.
Opinions expressed in forum posts are those of the poster, others may have different views.
Community Veteran
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Registered: ‎14-07-2009

Re: Line Threshold Speeds - "Acceptable Range"

Quote from: Jameseh
The FTR is set during the first 10 days. It is 70% of the MSR (Maximum Stable Rate) which is the lowest speed at which you sync during the training period.

Thanks, James, that is very helpful.  If you set a line to retrain, does that reset the MSR (i.e. you get a new MSR at the end of the re-training period)?
James
Grafter
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Registered: ‎04-04-2007

Re: Line Threshold Speeds - "Acceptable Range"

Yes.  If an SNR Reset is done, the training period is re run.
Community Veteran
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Re: Line Threshold Speeds - "Acceptable Range"

So if I fix an internal fault (say problematic telephone extension wiring) and thereby achieve a big increase in speed, then I should ask for a retrain to ensure that any fault that arises in future is acknowledged as such? Or, for that matter, if the router suffers a bad thunderstorm during the training period perhaps one should seek a retrain?
James
Grafter
Posts: 21,036
Registered: ‎04-04-2007

Re: Line Threshold Speeds - "Acceptable Range"

Theoretically yes.
JamesM
Grafter
Posts: 1,103
Registered: ‎24-06-2009

Re: Line Threshold Speeds - "Acceptable Range"

To clarify for me if you would please,
The BT speedtester says
For your connection, the acceptable range of speeds is 4 Mbps-21 Mbps.

Plusnet say
Estimated line speed:10Mb (This may vary between 8.5Mb and 12.5Mb)
So when would it be a fault, below 8.5Mbps or below 4Mbps ?
Community Veteran
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Registered: ‎15-06-2007

Re: Line Threshold Speeds - "Acceptable Range"

Neither
It is 70% of the lowest speed you had during the training period
JamesM
Grafter
Posts: 1,103
Registered: ‎24-06-2009

Re: Line Threshold Speeds - "Acceptable Range"

Thanks Jim.
So everytime a SNR reset takes place it gives you a new FTR. So the first SNR reset I had would have been when I was first switched over to 21CN. My sync was 13333, I can't remember what my speed was. So say for example my lowest speed was 12 Mbps, 8.4Mbps would be my FTR.
Now say my speed drops to 9 Mbps and I report a fault, I have another SNR reset but this time my lowest speed was 8 Mbps. So now I have a FTR of 5.6 Mbps even though my speed was 9Mbps but the lowest during training was lower than my original FTR.
So if the second FTR is lower than the first FTR which one is used ? Nearly confused myself there  Roll eyes
Community Veteran
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Re: Line Threshold Speeds - "Acceptable Range"

I don't know as I haven't had a retrain on my line just a noise margin reset - and no I don't know why
Of course in my case it is irrelevant since I am now synching way above the values during the training period and I don't know why but I am not complaining