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:-
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).