Hi tomtom,
There's no real way for you to accurately predict what you will actually receive until you go live, hence why they are estimates. ADSL speeds don’t give clear insight to how FTTC (VDSL) will perform on the same line since FTTC utilises higher frequencies and it is only the D-side and dropwire which are important.
Range A assumes a relatively clean line without bridge taps or wiring issues. This is the best case scenario speed and the DSL checker is usually pretty accurate, and over time the system does change its estimates based on conditions as it collects data – for one line here the downstream Range A has gone from 80-79 to 80-71 (High/Low) since the cabinet went live two years ago, but it still synchronises at the top end of the scale as it is free from bridge taps and apparent wiring issues.
I would say the 450m of crosstalk would already be taken into consideration with the estimate. The only way to find out how much impact would be to politely ask all of your neighbours using the broadband spectrum to switch off all their broadband hardware when you have FTTC
.
You are most likely to receive approximately the same speed as neighbours within the same geographical area and those on the same pole as yourself, give or take a few megabits depending on quite a few factors. However, bear in mind that the following will have an impact on what speed you can receive on FTTC (I will try and cover as much as I can):
- Distance
Distance leads to attenuation of the line. The shorter the better, but the attenuation is also amplified by the material and gauge alongside the distance.
- The material of the pair:
It can be either aluminium, copper or even a mix of both depending on when it was originally laid, and when parts of it have been replaced. Copper is a better conductor, and will attenuate less over distance. Aluminium is no longer implemented in networks post-broadband.
- The gauge of the pair:
The gauge of the pair has a bearing on attenuation, and 26 AWG (0.4mm) is the standard for Openreach from what I have read which apparently attenuates at 13.81 dB/km @300kHz. 24 AWG (0.51mm) is used in some cases, which fares better and attenuates less at 11.90 dB/km @300kHz. In some areas, they may use the thicker gauge to reduce attenuation in rural areas with long lines. But I have heard that in some areas that had lines laid pre-broadband may even use 26 AWG aluminium which can attenuate at a much higher rate and be more susceptible to interference.
- The quality of the pair:
If the pair has had sections repaired or replaced in the past, it may be subject to high resistance at joints. Furthermore, if there has been water ingress in any part of the copper network then there may be corrosion which can also lead to a drop in sync speed and more errors. Though, in this case, it would be classified as a fault if it is impacting the service.
- Filtering and internal wiring:
Since all new FTTC installs are self-install, unless otherwise requested or if the install is for a new physical line install, there will be no engineer so you will need to ensure your internal wiring is suitable and you are responsible for it. You can use the same filters you use with ADSL, but you may want to have a few handy just in case your current one is or goes faulty, or if the speeds are below what are expected. As for wiring,
http://www.kitz.co.uk/adsl/socket.htm may be a good read.
- Modem (chipset):
Choice of modem will have, in some cases, a large impact on what you can receive. Some modem/router combos provided by ISPs may come with a Lantiq broadband chipsets (like the BT Home Hub 5A and Plusnet Hub One). These chipsets may work well on short lines, lines less susceptible to interference and lines which are less subject to interferences. However, in my experience, Broadcom chipsets have always worked best when previously on a long line with ADSL2+ provisioned and even on a short FTTC line compared to Lantiq, allowing for a higher sync and less reported errors on the line. I do not think things have changed since then, and on a budget I would highly recommend a Billion 8800NL myself, and I imagine people here would say the 8800NL R2 is just as good (and it is slightly newer) as both come with a Broadcom chip.
- FTTC DLM (Dynamic Line Management) setting provisioned by ISP
This may prove to be a good read
http://www.kitz.co.uk/adsl/DLM.htm. Your ISP will provision you with a certain stability setting, and this sets out your error and resync tolerances before the DLM makes changes to “stabilise” your line. Since you are at the mercy of the DLM, even if things appear stable, it is ultimately the thresholds that will decide how stable the line is. Even if you experience only a short burst of errors, it may contribute to the threshold being breached if it is persistent, leading to the DLM taking action in an attempt to reduce errors (which in most cases will have a negative impact on sync speed).
All in all, the estimate of 19-27 Mbps on the downstream and 1.2-2.7 Mbps on the upstream seems reasonable based on your distance. However, I would not get your hopes up for it being that much faster than ADSL2+ on the downstream, but you may notice a decent uplift on the upstream.
re0