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[polymath]

I currently have ADSL2+ through a Netgear DG834GT. DMT v8.07 gives downstream information as follows:

sync speed 18208kb/s
attenuation 24.5dB
SNRM 2.8dB

The RCO is 85% (DMT gives a figure in brackets of about 21300kb/s - I guess this is the maximum attainable rate)

My ISP shows an IP Profile of 16Mb/s - that seems correct, it is .882 of 18.208

My maximum actual download speeds are about 1.8 Mbytes/sec or 14.5Mb.

In terms of FTTC I know our premises are about 1000m from the cabinet, and the exchange is about 1500m from our premises. Yes, the cabinet is quite a bit closer to the exchange (about 500m) than it is to our premises (1000m).

I have a couple of questions, I have tried looking in the FTTC section of the Forum and not found answers. If I have missed the obvious, point me at the right post.

The first question concerns speed versus distance graphs one sees on the web, e.g:

http://www.increasebroadbandspeed.co.uk/2013/chart-bt-fttc-vdsl2-speed-against-distance

Is the speed on such graphs the maximum attainable rate?

The other questions are:

Is the RCO value likely to be similar between ADSL2+ and VDSL or is it likely to depend on distance?

Is the factor between sync speed and IP profile the same for ADSL2+ and VDSL?

My interest in this detail is that on the basis of the speed versus distance graphs for ADSL2+ and VDSL 17a, the advantage of FTTC for our location might be marginal, and not worth the extra cost.

[Bald_Eagle1]

The first question concerns speed versus distance graphs one sees on the web, e.g:

http://www.increasebroadbandspeed.co.uk/2013/chart-bt-fttc-vdsl2-speed-against-distance

Is the speed on such graphs the maximum attainable rate?

I believe the speeds shown on such graphs are typical best case scenario sync speeds.

The other questions are:

Is the RCO value likely to be similar between ADSL2+ and VDSL or is it likely to depend on distance?

I'm not sure about that.

ColinS has previously posted messages in this forum referring to RCO.
It's not a value directly obtained from the modem's stats, but perhaps he explained how to calculate it from the stats that are available (The modem's firmware does have to be re-flashed though in order to view the stats as it is locked down as supplied by BTOR).

Until quite recently, BTOR supplied 2 types of modem.
The Huawei HG612 modem is preferred to an ECI modem as it is very easily unlocked & there are a couple of feely downloadable stats monitoring packages available for 24/7 connection monitoring.


I believe BTOR are still supplying those modems for engineer managed installations (you need to use a separate router with those modems) & a BT Home Hub 5 for self installation (where the engineer only carries out work at the cabinet).

Is the factor between sync speed and IP profile the same for ADSL2+ and VDSL?

No. IP Profile for VDSL2 connections is 96.79% of sync speed.

My interest in this detail is that on the basis of the speed versus distance graphs for ADSL2+ and VDSL 17a, the advantage of FTTC for our location might be marginal, and not worth the extra cost.

I live between 1000m & 1100m from the cabinet & these are my current connection stats:-

Max:   Upstream rate = 4983 Kbps, Downstream rate = 22212 Kbps
Bearer:   0, Upstream rate = 4928 Kbps, Downstream rate = 20488 Kbps

The Bearer details are the actual sync speeds & Max are the theoretical attainable rates.



So, my IP Profile should be 96.79% of 20488 Kbps i.e approximately 19830 Kbps.

According to the BT Wholesale Broadband Performance Test, it is indeed 19.83 Mbps:-

Code: [Select]

1. Best Effort Test:  -provides background information.

 Download Speed
 17.33 Mbps
   
0 Mbps 19.83 Mbps
Max Achievable Speed

 Download speed achieved during the test was - 17.33 Mbps
 For your connection, the acceptable range of speeds is 12 Mbps-19.83 Mbps .
 Additional Information:
 IP Profile for your line is - 19.83 Mbps

2. Upstream Test:  -provides background information.

 Upload Speed
 4.44 Mbps
   
0 Mbps 10 Mbps
Max Achievable Speed

Upload speed achieved during the test was - 4.44Mbps
 Additional Information:
 Upstream Rate IP profile on your line is - 10 Mbps


I have a 40/10 service & upstream IP Profile is aways reported as the maximum service speed i.e. 20 Mbps, 10 Mbps or via one or two suppliers still only 2 Mbps.


My connection did achieve around 30Mbps sync speed for a number of months until it gradually deteriorated, assumed to be due to increased crosstalk as more users were connected.

If you did opt for VDSL2 (FTTC), you are not likely to gain that much in the way of improved DS sync speeds, but IP Profile & therefore actual throughput might be better than ADSL2+ (until crosstalk reduces speeds).

In time, Vectoring is likely to assist in reducing the effects of crosstalk (that's the hope for my connection anyway).

However, you would be very likely to see improved US sync speeds/throughput.

In my case (around 5.4km from the exchange) I was lucky to achieve around 1 Mbps DS sync speed on ADSL (& then only on a good day, with the wind in the right direction).

[ryant704]

Here are my stats, 965m + Up and down poles.

xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason:   0
Last initialization procedure status:   0
Max:   Upstream rate = 5302 Kbps, Downstream rate = 26448 Kbps
Bearer:   0, Upstream rate = 5308 Kbps, Downstream rate = 28160 Kbps

Stayed about the same, I have the best service I have had since the start (September 2012). I was around 20Mbps until the majority of the REIN was removed in my area and crosstalk has came into affect as well for me.

[Bald_Eagle1]

Stayed about the same, I have the best service I have had since the start (September 2012). I was around 20Mbps until the majority of the REIN was removed in my area and crosstalk has came into affect as well for me.

That's great news.
I may have missed it, but did you ever discover the actual cause(s) of the REIN issue(s)?

[Greybeard33]

Just to add to the previous replies, I would recommend you refer to BT Wholesale Availability Checker for an estimate of FTTC speed. From discussions elsewhere on this forum, it is far from perfect, but likely to be more accurate than a rough estimate based only on line length. Speed also depends on the type (aluminium or copper) of cable and its condition, on levels of electromagnetic interference along the line, and on the effect of crosstalk from other FTTC lines in the same cable. Also it is difficult to estimate the length of the line from above ground - the duct may zig-zag from one side of the road to the other.

Unless there is a fault on the line, the speeds you get should be somewhere between the Range A High and Low estimates - to avoid disappointment I would assume the Low figures when deciding if the extra speed is worth the higher cost. As BE said, for your combination of line lengths, the improvement over ADSL2+ is likely to be much greater for uploads than for downloads.

As an example of a better line than Bald Eagle's and Ryant's, the D-side length of my line is probably a little less than 1000m. The checker gives ranges of 28-38.4 down, 6.4-7.9 up. My actual sync speeds are 39.998 down, 7.792 up, giving an IP Profile of 38.72. The E-side is about 800m, and I used to get a sync speed of about 15-18 on ADSL2+. I find the FTTC improvement of about 2.5* the download speed and 6* the upload speed well worth having.

[waltergmw]

@ Greybeard,

Although almost certainly not worth paying a premium rate, it should be noted that your 40 Mbps line performance is probably limited by a banded or capped profile. If so the maximum download speed of your line could possibly be a little higher.

Kind regards,
Walter

[ryant704]

Stayed about the same, I have the best service I have had since the start (September 2012). I was around 20Mbps until the majority of the REIN was removed in my area and crosstalk has came into affect as well for me.

That's great news.
I may have missed it, but did you ever discover the actual cause(s) of the REIN issue(s)?

A small one was originating in the cabinet, the other was in another persons property. That's the only details I've been given (I'm pressing for engineers notes but I doubt I will get them) but the investigation is still on going.

[Greybeard33]

@ Greybeard,

Although almost certainly not worth paying a premium rate, it should be noted that your 40 Mbps line performance is probably limited by a banded or capped profile. If so the maximum download speed of your line could possibly be a little higher.

Kind regards,
Walter

Correct - in fact I have now downgraded to a 40/10 service (Infinity Option 1 Unlimited), although at the time of the last resync I was still on Infinity 2 (80/20). I believe the line was previously DLM-banded to 40 Mbps max, since the highest DS sync I ever saw was exactly 40000 kbps. In any case it is running very close to its maximum capability, with DS SNRM fluctuating between 6 and 7dB and max attainable rate 47-49M (interleaving on). At times in the past sync speed has been as low as 35 Mbps, although the recent HG612 firmware upgrade (and/or the associated Huawei DSLAM band plan tweak) seems to have improved performance and stability slightly.