FTTC speed prediction lower for flats?

I am intending to switch to BT Infinity shortly, but was slightly disappointed with the speed predictions: around 48 Mbps download and 8 Mbps upload. I am about 250 metres from the cabinet (the BT Wholesale checker helpfully confirms which cabinet I'm served from). I decided to check what sort of speeds some of my neighbours would get, and discovered that houses in the same road, which are maybe 50 or 100 metres further away from the cabinet, are predicted to receive 56 down and 16 up.

Why would the prediction for my flat be so much lower? Do BT predict lower speeds for flats because they assume poor internal wiring or something? The ADSL 2+ speed it predicts is pretty close to what I get, but I note that it predicts lower speeds for same neighbouring houses. Why is their ADSL predicted to be lower speed, but FTTC higher?

The likely speed I can expect is important as it could determine whether I go for Option 1 or 2 (given that the former is now available as an Unlimited option). Any explanations of how the predicted speed is determined would be appreciated.

That's pretty poor speed estimate @ 250m from the cabinet. I'm guessing either the estimate is way off, the flats are off a different cabinet, or the D sides take a long route to the flats

In reply to a post by Ribble:

... or the D sides take a long route to the flats

Yes, to the OP - are you measuring your distance from cabinet as the crow flies, or the likely path it takes via overhead cabling and/or footway boxes? Using Google Maps and its measuring tool, I'm 143m from my cabinet in a straight line, but when plotting the course of my line's route to the cabinet, it's 329m. So if you were measuring in a straight line, and the percentage increase between that distance and the cabling distance to cabinet is similar to mine, your copper VDSL link to the cabinet could be something like 600m.

For me the checker estimates 66.9 down, 20 up. So if your actual line is twice as long as mine, that makes some sense, although I still think it's a bit low, like Ribble. There's also a huge disparity with the upstream estimates.

Edited by gazzyk1ns (Wed 06-Mar-13 06:02:09)

I guess it would lso depend how the phone line is routed within the building. OP doesn't say how big the block is that he lives in.

I lived on the 4th floor of a block of flats years ago and all the phone lines came into the building to a central junction box in the basement. From there the lines were routed through ducting to the various floors. I would probabaly estimate my line was about 400m long just within the building.

my house is 3 flats.

They all share the same dropwire so it may be related to the extra crosstalk expected from that?

The predictions also use information on how your ADSL line was performing relative to others locally in terms of noise.

Being in flats means that there is a possibility of a greater density of local noise/RFI from the various electrical/electronic appliances. Cross talk might affect the Upstream to a greater extent but on the Downstream the pairs will be running together from cabinet to building so the additional few metres will not do much.

Ideally in a block of flats, if there was access to the point where all lines entered, it would be ideal if you could install the modems there, and then run Cat5e for data and use the existing phone pair for voice.

In reply to a post by MHC:

The predictions also use information on how your ADSL line was performing relative to others locally in terms of noise.

Being in flats means that there is a possibility of a greater density of local noise/RFI from the various electrical/electronic appliances. Cross talk might affect the Upstream to a greater extent but on the Downstream the pairs will be running together from cabinet to building so the additional few metres will not do much.

Would this have such a great effect on FTTC but not on ADSL 2+? My predicted speed for ADSL 2+ is correct, and is higher than for the very same houses that seemingly have better FTTC speeds.

In reply to a post by Ribble:

That's pretty poor speed estimate @ 250m from the cabinet. I'm guessing either the estimate is way off, the flats are off a different cabinet, or the D sides take a long route to the flats

As I said, the BT Wholesale checker tells me which cabinet I'm on, it matches the stencilled number on the cabinet and is the same for the houses.

Obviously I don't know the route the cables take, although if they took a more roundabout route, they'd pass the houses first, in which case they should have a higher ADSL prediction too. It's the discrepancy between the predictions for FTTC and ADSL2+ I really don't understand.

Thanks for all the replies so far.

If I do go for Infinity Option 2 and discover the speed makes it not worth it, will BT let me downgrade to Option 1? I have searched old posts and it seems they will allow downgrades, although they reset the contract length to 18 months. Could anyone confirm that?

I will of course post results of what speed I actually get!

They could be on a completely different E side cable to the exchange