I'm of the opinion that 2km is very much a problem.
Unfortunately, it is one of those areas that is hard to be even semi-accurate about. Some searches online suggest that BT's practical limit is around 1500 metres - but everyone is focussing on what is happening to the downstream speed at this distance (particularly when BT was limiting downstream to 15Mbps), and the race to 80/20 speeds may have impacted on lengthier lines; some VDSL2 products specify 2km as the maximum distance (such as this one
), while this card
has dropped to 16 down, 0.3 up at 5,000 feet (1600 metres). This primer
asserts that VDSL2's long reach is up to 2.4km.
Some of the semi-technical write-ups specify that VDSL2 starts to behave like ADSL2+ at the 2km point. Wikipedia mentions this (but it also mentions a LR-VDSL2 protocol for long range). ZDNet had this to say
a while back.
Practical experience (but only from seeing what other people post; it isn't first-hand experience) makes me think that it is really upstream
that is the limiting factor on extreme distance cases - and that the UK variant of VDSL2 is not behaving like ADSL2+ at distances beyond that. I'm not sure if that is a consequence of the way we use the US0 band for the final, longest range, upstream capability. Or the way we use the power levels of our 17a profile or, more particularly, the power masks applied over the low frequencies so the cabinet does not interfere with exchange-based ADSL (and ADSL2+) - although they're more for downstream than upstream.
Or perhaps BT's upstream power-backoff mechanism is tuned for short lines, rather than long lines. Even though it only applies to the power in the higher-frequency bands, the tuning does make a difference to the upstream speed available out at 1500 metres. Take a look at this document on The art of spectral management, UPBO
, especially page 3. I guess BT have used a reference length close to the first 2 graphs.
(BTW: There's also a matching document on The art of Spectral Management, Frequency Allocations
As bald-eagle notes - that 1600 metre line could still manage 12.7Mbps down, but only 0.7Mbps up. and one device predicted 0.3Mbps up.
Is it worth installing FTTC lines when the upstream speed is getting lower than 0.3Mbps?