Broadband speed just suddenly almost halved.

[bobbear]

Thanks for the reply. No, I am not confusing line sync rate with data rate, which as you say is affected by contention and congestion. Providers seldom if ever say what speed they are talking about when they refer to "download speeds" which doesn't help, but the only real-life speed that matters is the data rate, and line sync rate can only be measured by the modem/router anyhow. Even your diagram below doesn't specify what "speed" it is referring to..('connection speed' is non-specific). In any event under little or none contended situations the difference between the two should only be in the region of the overhead margin. (Yes - I spent 30 odd years in an IT related industry..).

I've eliminated my internal extension wiring and connections by connecting directly to the V1.0 faceplate rear socket via an ADSL filter and also changing the Smart Home Hub2 & it's input lead with a for a Billion 8800N modem router plus new lead with no discernable difference. I cannot see what more I can do. The only thing I can't eliminate, (who can?), is the short length of cable that runs from the V1.0 rear connections to the outside BT junction block. Technically I am perfectly capable of replacing the crappy original CW1308 cable with a nice new bit of XCM90 Cat6 PE cable, but I'm not allowed to do that, am I?

Fortunately its easy to trace the cable distance of the Woodchurch cabinet 2 from my home up Redbrook Street (TN26 3QU) fairly accurately as the rural distribution is mostly overhead and visible and it's in a straight line down Redbrook Street from my house to the cabinet, so 2.5km (using Google maps is pretty close - allow +10% for loops and minor deviations if you like...

It's good to see from your diagram, (thanks for that), that I should be achieving nearer 10Mb/s "connection speed" (I wish - even line sync rate..). Currently the line sync rate from the Billion is 3,399 Mbps  resulting an Ookla speed test (https://www.speedtest.net/result/12046612925) of 2.96/0.74, the upload once again being outside of the 'stayfast guarantee' range, but I have seen the line sync rate down as low as 2.5Mbps, giving a data rate below 2Mbps.

Would you be happy with broadband at that speed, especially as I used to 'enjoy' >5Mbps not that long ago..?

Lets face it, if there is indeed no throttling by Openreach to alleviate system congestion, (notice I don't say 'BT'..), then my line must be duff.

[imjolly]

ISP quote connection speed not download speed - no ISP guarantees download speed.  It can be confusing as even BT talk about download speed but clarify in the T&C that any reference to download speed is actual connection speed.

The graph gives a good idea of speed over distance but is on good quality line and as you posted I doubt your long line from cabinet is classified good.

You still don't have a stable connection and won't make any progress until that problem is fixed

[licquorice]

Replacing a couple of metres of perfectly good cw1308 cable after the signal has traversed 2.5Km of distribution cables isn't going to make a jot of difference. 

It is possible your problem is being caused by a new crosstalk disturber having been provided recently.

[bobbear]

Totally agreed.. Perhaps a little pedantic, but I still maintain 'connection speed' is not an accurate use of language - perhaps 'data transfer rate' and 'line sync rate' are more accurate with regard to the actual connection, but then you add contention into the mix wrt the former..

I also doubt that my line is classified as a good one..(but it used to be stable and with an acceptable performance until recently..)

Yes, you're right - I don't currently have a stable connection, but I'll never have a stable connection if the line won't support it.. so how do I get it fixed? BTCS wouldn't accept that there is any problem that they could report to Openreach.

[bobbear]

Thank you for that. Quite right - 10metres of CW1308 aren't going to make any difference, although you have to be a bit careful before ruling it out - when the BT engineer installed it initially I found he'd stapled through it in a couple of places when he secured it round a door frame with a staple gun which didn't help ..

That's an interesting suggestion about "new crosstalk disturber", whatever that is. Thank you for that. Although as a retired RF systems, hardware & networks engineer I'm familiar with the overall picture & technicalities - I'm not familiar with the nuts and bolts of the system. Some sort of change of that nature is exactly what seemed to occur.

[licquorice]

Crosstalk is the bane of VDSL, if a new customer has just been added their circuit could be interfering with yours. Unfortunately there is no fix for crosstalk if that is the cause of the problem. There were some trials carried out with vectoring to mitigate the effects of crosstalk, but I don't believe it was implemented universally.

[bobbear]

I see what you mean, now. Thanks - yes, I'm familiar with the problems of crosstalk in multi-twisted pair cables which generally increase proportional to frequency. It might I suppose be possible to select a pair that is less affected, if indeed there is one in the cable. It would be nice to be able to reliably access catch-up TV again like I used to be able to do..

[bobbear]

Update:

Interestingly enough, having tried leaving the router on for periods in excess of the usual "ten day settling period" with no improvement in the downstream line rate, (which prior to the VDSL2 'Superfast" 'upgrade' earlier in the year used to sync up on ADSL2 at different speeds due to the variability of the line, noise, crosstalk etc, but usually in the region of 6Mbps, giving me a downstream data rate of c. 5Mbps), I now save myself some electricity costs and switch the router off every night. Every single morning without fail when I switch it on it syncs up at EXACTLY 3.095 Mbps downstream rate, (at 8.4dB S/N this morning), giving me a downstream rate of c. 2.5Mbps. You don't need to be Hercule Poirot to realise if that is not indicative of a preset downstream line rate limit I don't know what is... It is very frustrating knowing that my line was obviously capable of a better downstream speed on ADSL2 but has now been handicapped to the extent that accessing any on-demand video service is now problematic if not impossible where once it was no problem. Safe to say I now regret the VDSL2 "Superfast" 'Upgrade', (talk about a misleading promotion), and every time I see one of the countless adverts for "Superfast" broadband I have an almost irresistable urge to hurl a brick through the screen... Fortunately the wife has banned bricks from the living room, but the cat gives me a wide berth...

[imjolly]

unlike adsl2 your vdsl takes a lot longer for the DLM take action to reduce your noise margin which will increase connection speed to nearer attainable assuming line is silent with no noise.  switching hub off at night and on next day is not going to see any improvement in connection speed as a stable 24/7 connection is needed and could take a few weeks before you see any change by DLM

[bobbear]

Thanks for the reply.

Another good reason to reject a VDSL2 so-called "Superfast" 'Upgrade' if you are offered and have a long line.. On my old ADSL2 service the DSLM negotiated the best possible speed for the target S/N ratio every time I switched on - no need to pointlessly waste expensive eco-unfriendly electricity leaving your modem/router powered 24/7. Not only that, but if you used a decent modem router such as the Billion with the Broadcom chipset, you could manually tweak your target S/N in real time on ADSL2.

It's funny how the goalposts seem to change all the time with BT - so "Ten days" has now become "a few weeks" which is vague and not terribly helpful - I've certainly left it on "a lot longer" than ten days with no effect, so no - that doesn't work - and what about the frequent power cuts around here resetting everything to square one? (we've got a scheduled outage tomorrow, for example). Not only that but when I complained to BT C/S about my 2.5Mbps speed I was told: "Sorry, but your stayfast guarantee speed is 2Mbps so stop bothering us" (or words to that effect). When it dropped below 2Mbps I complained again and was told "Sorry, but your personal stayfast guarantee speed is 1Mbps so stop bothering us" (or words to that effect - , (note the subtle difference in wording), yet I notice that in BT's latest adverts for their "Superfast" "fibre" service for my line they are now quoting a stayfast guarantee of 3 Mbps with a downstream range of 4Mbps-8Mbps. That is wrong and especially misleading if they are talking about line rate.

When I was 'offered' the 'upgrade' in 2020, (I don't recall I had much choice - I was just sent an unsolicited  Smart hub2 in the post), I was led to believe that there would be at least no degradation of the service, (estimated speeds for the proposed service were quoted as 4Mbps-7Mbps, (same as my old ADSL2 so I thought "fair enough"). Any reasonable person would expect to be in the middle of that range), well I'd call a 50% D/S data rate speed drop from 5Mbps to 2.5Mbps a degradation of service. I for one am not happy about basically being misled. The other point is that when my VDSL2 service first went live, I was getting the quoted speed range, but after 6 months or so dropped to what it is now.

Sorry, but even with an initial high S/N ratio, the negotiated rate should vary each time the router is powered due to line variabilities, so I'm afraid that your reply doesn't hold water. The fact that I ALWAYS connect at exactly 3.095Mbps is evidence of a rate cap. I shall be interested to find out what Ofcom have to say on this issue.