I was wondering if the TBB FTTC speed estimation process for superfast coverage takes into account the exchange-to-cabinet distance as, despite what is commonly quoted it's not just the cabinet-to-property distance that matters (at least in the UK).
This may seem odd, but the reason is in the detail of the ANFP (Access Network Frequency Plan).
The purpose of the ANFP is to permit the co-existence of multiple services over the phone network so that they don't unduly interfere with each other. One important part of the ANFP is to allow VDSL and ADSL2+ to co-exist on the same network. This is achieved by controlling the power of signals at the cabinet from "swamping" the weaker ADSL signals from the exchange by excessive cross-talk using what's called a PSD mask. Of course the simplest way to achieve this would be to eliminate any frequency overlap at all. However, what the ANFP does is much more subtle. It allows for increasing of ADSL2+ frequencies as they become attenuated to the point of being useless according to the cabinet's distance from the exchange. Interestingly this means that cabinets further from an exchange in rural areas should be able to offer service over a longer range than would otherwise be the case as it's precisely those lower ADSL2+ spectrum frequencies (in the 0.1-2.2 Mhz region) that travel furthest.
See the ANFP and particularly the section on PSD and what's called the Cabinet Assigned Loss or CAL, which is a characterisation of each cabinet position according to the electrical characteristics of it's position with relation the the exchange.
I noticed this on moving house recently. From my previous cabinet about 4km from the exchange and 640m distant from hone, I could get 58mb downstream and just below 10mb upstream. At the new house, about 900m from the exchange and a cabinet about half way, the maximum data rate downstream is again about 58mb, yet upstream the maximum data rate is 22mbps (although capped to 20mbps of course). The reason for this can only be down to the virtual elimination of any ADSL2+ frequencies from the downstream PSD in the latter case as, at 400m from the exchange, all those frequencies are usable so must be protected. In contrast, at my previous cabinet, much further from the cabinet, some of those ADSL2+ frequencies were so attenuated as to be useless and were hence reused by the VDSL service.
Unfortunately I don't have a router which can give me the bit loading profile, but it's wholly consistent with the theory.
What this also means is that it's rather difficult to build in maps of expected speed by using solely cabinet to consumer distances. The distance from the exchange must also be taken into account. I wonder if ThinkBroadband's assessments have taken this into acount?