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Author Topic: G.Fast - Understanding a difference of information between ISP and Openreach  (Read 2600 times)

spudgun

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Good afternoon all,

This isn't a problem as such, but i've raised this so that I can add to my own knowledge and understand my line and G.Fast technology a little better.

I've had a visit from a fantastic and helpful Openreach engineer this week in relation to my G.Fast circuit.

According to his measurement equipment (see pic below) that was plugged in to my line, it is capable of 253mb or thereabouts.



This is broadly similar to the maximum observed rate that is noted for my line via the Openreach database (see image below) - please note that the engineer reading and max observed rate are both on the same day.



There is a difference between the sync speed that is reported on my ISP's portal, however, (see image below)  The measured throughput on my line (setup is a MT992 + AC68-U running latest Merlin) is consistent with the sync speeds that my ISP is reporting when overheads are taken into account.



Does anyone know why there might be such a big difference between Openreach's information and that from my ISP?

I look forward to seeing what the experts on here make of this :)
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burakkucat

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I will offer the opinion that any measurements made by Openreach will show what the circuit is capable of achieving without considering any overheads; any service provider's profile modifying/adjusting/tweaking/banding the result.

The Openreach G.Fast Closeout Test reports: 253 Mbps DS / 30 Mbps US
The BT Wholesale checker reports:           247 Mbps DS / 30 Mbps US
Your ISP (is that Zen?) reports:            229 Mbps DS / 30 Mbps US

(All rounded to the nearest whole number Mbps.)

To me, that table of results looks reasonable. But I may have missed something significant. So I shall watch for comments from other members.  :)

[Edited to correct the error.]
« Last Edit: June 28, 2019, 03:51:30 PM by burakkucat »
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spudgun

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Thank you for your input, that was my first thought too - but probably not  wise by openreach to have that on their website as some people might expect to get the 'no overheads' speed and raise issues.

I can confirm that Zen is the ISP and your summary is accurate (apart from the Zen upstream that is 30mb in line with the other two).
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burakkucat

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. . . probably not  wise by openreach to have that on their website . . .

To me, that looks like the output from the BT Wholesale Broadband checker.

Quote
. . . (apart from the Zen upstream that is 30mb in line with the other two).

Post edited to correct my error.
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ejs

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Perhaps it's simply that the Openreach tester is the better modem.
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kitz

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^ Possible!
Without any stats from the MT992 we are working blind.   :(

Also there is the possibility that DLM could have changed something which affects the sync speed.  I'm not sure if recent FTTC DLM amendments also follow over to g.fast or not, as g.fast wasn't mentioned.   
So I suppose there is a chance that the line was on full open profile when the engineer performed his tests but after a day the default DLM profile has kicked in - whatever that is for g.fast?     It was last year when the engineer ran tests on my daughters line but I know he reset DLM to Open yet a few days later they had interleaving applied.   

You may be able to spot interleaving based on latency - however that could depend where you live and which Zen gateway you are going through.   
If you are on their Manchester PoP and live down South it could be harder to tell.   With my daughter living up north, being on their Manchester PoP makes no difference to their overall latency.

----

PS - For clarification:

Zen are seeing you sync at 236737.
229151 is your IPprofile
TR101 basically just means Ethernet backhaul (21CN WBC/WMBC).
Interleave Auto - means can be on or off as dictated by DLM.  This is historic from the days of ADSL as it can't be set as off when on VDSL

You many be able to get Zen to give you your DLM profile if they run a GEA test - although it does sometimes lag behind by 2 weeks.
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How to get your router line stats :: ADSL Exchange Checker

adslmax

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There seem to be Pro's & Con's on gfast there. Don't understand why BT Openreach tester get a better result than BTw estimated and Zen profile on it.
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kitz

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Quote
Don't understand why BT Openreach tester get a better result than BTw estimated and Zen profile on it.

If you read the rest of the thread, there's several reasons given as to why this could be :/
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waltergmw

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For those who haven't looked recently the BT Openreach data (which often used the BT W "Impacted" figures) has now been withdrawn so Openreach now only provide some cabinet location details.
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Chrysalis

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The BTw estimates are most definitely sync speed (before overheads), not throughput.

Openreach testing kit the same.

The reason been both entities are not responsible for throughput.
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spudgun

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Apologies for the delay in responding to all of the kind and helpful points made above, but I've been away for the weekend.

In response to the points raised, I am in Gloucestershire, and have previously raised a ticket with Zen to ask to have my routing not go via Manchester to London as that makes no geographic sense and they have taken care of that. Whilst I was going via Manchester pings were about 16ms to bbc.co.uk, but with London routing this is now either 9 or 10ms. My estimates of distance travelled against speed make me believe that this connection isn't interleaved, but I will stand corrected if the experts here can find fault in my logic.

I agree that the lack of stats from the MT992 make understanding G.Fast difficult and that is one of the reasons that I raised this post as sharing knowledge/experience is perhaps the best way that we can build up a limited understanding.

I did get a look at a separate screen on the device that the engineer was using that gave the snr info for my sync (sadly no photo of this) and that was 3db up and down - which i understand to be the default for g.fast - and the engineer believed that to be the case too.

The difference between the testing device and BT wholesale information is made a little bit more strange as I spoke to Zen on Friday night before I left and they said my line was synced at 247mb (which matches the BT wholesale observation) - but the line data that is available on their own pages contradicts this (posted in the OP) and the max throughput that I am seeing matches exactly the downstream of 229 (sync of 236).

Don't get me wrong, I'm not complaining or anything here for a line length of 310m (again measured by the engineer's kit) I think i've done really well and the line was really stable until all of the underground chambers flooded about 2 weeks ago and knocked everything out (including making voice calls very difficult - and this is why the engineer visited!), but I am actively interested in technology (as many here probably are), so thought this might be worthy of discussion.

« Last Edit: June 30, 2019, 10:12:27 PM by spudgun »
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re0

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I had to do the same on Zen in regards to routing. Initially, they were reluctant and refusing to change my routing via email (and maybe telephone). However, I had raised a fault for low single-thread speeds and as soon as I mentioned to them about the routing, they changed it to London from Manchester since apparently it was a mistake. Not only did this reduce my latency to as low as 9-10ms, but also fixed the single-thread speed issues.

There aren't that many places in Gloucestershire that have G.fast. Cheltenham has had it for a while, and the pods have been around there for some time. I haven't noticed any further popping-ups of pods in other cities and towns personally.

If you're interested in stats, I would recommend the XMG3927-B50A. You can find the stats in the UI and also use SSH/telnet, and it is possible to use DSL stats with (as I do, with the Raspberry Pi).
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j0hn

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The default target SNR is 3dB but the DLM is considerably more flexible on G.Fast and can go up/down in 1dB increments.
I've seen it go as high as 15dB.

I'd be surprised if the line was as long as 310m.

What was the attenuation on VDSL2?
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spudgun

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I'm really sorry, but I can't remember what the attenuation was on VDSL and I don't have any stats logs saved. I was on the full 80/20 which dipped to 76/20 about a month before G.Inp was launched, after which the full 80/20 was back.

The engineer's kit definitely said 310m as I remember that most clearly from when he was here and my best guess is that is about 50m more than a direct line route (based on nothing more than me pacing it out) so I have no reason to doubt its accuracy.

I think I've read on here that A+A will sell you one of those Zyxel boxes - any idea how much we are talking about as I might think about it next pay day?
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burakkucat

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I think I've read on here that A+A will sell you one of those Zyxel boxes - any idea how much we are talking about as I might think about it next pay day?

Rumoured to be in the  order of 100 - 150 (ex.VAT), 120 - 180 (inc. VAT) :-X

[Edited to account for VAT.]
« Last Edit: July 01, 2019, 05:32:59 PM by burakkucat »
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