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Standard User Colin_London
(member) Tue 30-Jul-13 00:54:29
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Which tester is most accurate for FTTC line profile?


[link to this post]
 
I have always used the BT Wholesale tester site up until now to report my Infinity line profile:

http://www.speedtest.btwholesale.com/

My profile has been fixed to 52.27Mbps (with a downlink throughput to my PC of c.51.9Mbps) for some months now following previous line faults according to this site.

However tonight I tried the tester at:

http://diagnostics.bt.com/login/?workflow=Speed

And this reports the linespeed 'between the exchange and your homehub' at 53.8Mbps (despite the Wholesale tester still reporting 52.27). The downlink throughput to my PC is shown as 51.2Mbps.

I am presuming that my linespeed cannot be higher than my Profile can it?

So which is the correct figure for my profile, 52.27 or 53.8?

(NB: The maximum prediction for my line is now 54.2 following the recent reductions in estimates).

Edited by Colin_London (Tue 30-Jul-13 00:58:07)

Standard User Ignitionnet
(knowledge is power) Tue 30-Jul-13 05:16:58
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Re: Which tester is most accurate for FTTC line profile?


[re: Colin_London] [link to this post]
 
In reply to a post by Colin_London:
I am presuming that my linespeed cannot be higher than my Profile can it?


Not just can be, but has to be higher. The lower figure is correct for IP profile, the higher figure correct for line speed.
Standard User yarwell
(sensei) Tue 30-Jul-13 09:26:20
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Re: Which tester is most accurate for FTTC line profile?


[re: Colin_London] [link to this post]
 
In reply to a post by Colin_London:
So which is the correct figure for my profile, 52.27 or 53.8?


1st world problem smile

Depends if they're using the same definition, the " the linespeed 'between the exchange and your homehub' "probably isn't the IP profile but the sync speed / line data rate.

--

Phil

MaxDSL - goes as fast as it can and doesn't read the line checker first.

MaxDSL diagnostics


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Standard User billford
(elder) Tue 30-Jul-13 09:30:34
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Re: Which tester is most accurate for FTTC line profile?


[re: yarwell] [link to this post]
 
In reply to a post by yarwell:
Depends if they're using the same definition...
Or the same units- the ratio between them is ~1.029, suspiciously close to 1.024 considering the number of decimal places given.

So they could both be right smile

Bill
A level playing field is level in both directions._________________Planes and Boats and ... ______________BQMs: IPv4 IPv6
Standard User StephenTodd
(experienced) Tue 30-Jul-13 09:58:18
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Re: Which tester is most accurate for FTTC line profile?


[re: billford] [link to this post]
 
I'm almost certain that the http://diagnostics.bt.com/login/?workflow=Speed tester just queries the IP profile, multiplies by the magic number to guess the sync speed, and reports that as if it is the sync speed.

In normal situations that gives the right answer to sync speed. However, when there is a difference (eg when things are interesting, stale/stuck IP profile) the number it gives is not very helpful, and the way it presents it is just misleading.

http://www.speedtest.btwholesale.com/ doesn't give the answer in such a pretty way, but at least it's unadulterated.

--
Moved (with trepidation turned relief) to BT Infinity 2 for upload speed. Happy BE user for several years.
Standard User Colin_London
(member) Tue 30-Jul-13 22:20:51
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Re: Which tester is most accurate for FTTC line profile?


[re: StephenTodd] [link to this post]
 
Except that when I used the diagnostics.bt.com website when I was using my Airport Extreme router it refused to give me a linespeed, but now I am using a Homehub 4 it does. Makes me suspicious that there is something in the claim that it is querying the homehub....
Standard User yarwell
(sensei) Wed 31-Jul-13 09:32:17
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Re: Which tester is most accurate for FTTC line profile?


[re: Colin_London] [link to this post]
 
or maybe Apple don't comply with the standards so the PPPoE negotiation doesn't send the linespeed upstream.

--

Phil

MaxDSL - goes as fast as it can and doesn't read the line checker first.

MaxDSL diagnostics
Standard User StephenTodd
(experienced) Wed 31-Jul-13 13:50:47
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Re: Which tester is most accurate for FTTC line profile?


[re: Colin_London] [link to this post]
 
The HomeHub doesn't know the sync speed: only the modem and cabinet know that.

Now I think of it, I'm not sure how the sync speed information gets back to the exchange or whereever on PPPoE connection to allow the IP profile to be set.
Maybe the HomeHub does know, but just won't let on to the customer. Anyone?

Either way, I still believe my earlier statement that the retail speed test only knows the IP profile and not the sync speed.

--
Moved (with trepidation turned relief) to BT Infinity 2 for upload speed. Happy BE user for several years.
Standard User greenglide
(experienced) Wed 31-Jul-13 14:05:57
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Re: Which tester is most accurate for FTTC line profile?


[re: StephenTodd] [link to this post]
 
The HomeHub doesn't know the sync speed: only the modem and cabinet know that.

Now I think of it, I'm not sure how the sync speed information gets back to the exchange or whereever on PPPoE connection to allow the IP profile to be set.
Maybe the HomeHub does know, but just won't let on to the customer. Anyone?


Well the SKY router knows so BT could use the same.

The test doesnt work on my FTTC connection - presumably because the Home Hub is in the box where it belongs and my Cisco Linksys router is in use.

BT Infinity 2 - IP profile 77 / 20 - super fast!
Previously BE Unlimited - 21,000 Download 1,200 Upload but then moved house - 6,500 Down, 1Mb/s up - gutted!
Ex <n>ildram , been to SKY MAX - 15,225 Download
Standard User RobertoS
(sensei) Wed 31-Jul-13 16:33:25
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Re: Which tester is most accurate for FTTC line profile?


[re: greenglide] [link to this post]
 
The Sky router knows because Sky send the info to it.

The sync speed on FTTC is sent upstream by the Openreach DLM on establishment of the PPP session, and it is up to the wholesaler (BTW/Sky/TT) what they do with it.

BT Wholesale appear to feed it into their own DLM which sets the IP Profile. From (Openreach) SIN 498:-
The CP is expected to shape the downstream traffic to match the actual VDSL2 line rate in order to avoid excessive traffic loss.
CPs should be aware that the mechanism for reporting the downstream and upstream line rates relies on a line re-train causing the CP, or the CPE, to initiate a new PPP session or a new DHCP request. The success of this method of line rate reporting is down to the CP's choice of timers used around PPP/DHCP handling.
If the PPP/DHCP survives a re-train, then the CP will be unaware of any change in the line rate and will not be able to shape appropriately.
The line re-train time for VDSL2 can be anywhere between 10 and 60 seconds, with typical values in the 20-30 second range.


My broadband basic info/help site - www.robertos.me.uk | Domains,website and mail hosting - Tsohost.
Connection - Plusnet UnLim Fibre (FTTC). Sync ~ 51.8/16.8Mbps @ 600m. - BQM

"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Allergy information: This post was manufactured in an environment where nuts are present. It may include traces of understatement, litotes and humour.
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