A Question for those who know about such things ............

[Ardua]

Am I right in saying that the only thing that an independent ISP can control on a FTTC line is contention, and that congestion and VDSL crosstalk issues sit firmly with BT?  If that is the case, and given that Infinity take up seems to be increasing, what is likely to have the biggest effect on end-user download speeds?

[Rik]

AFAIK, BT always control contention.

[Lance]

Although an ISP can prevent contention within their own network.

[Rik]

Indeed they can.

[mervl]

I'm no expert on these things (as you can tell) but:
1. As the largest FTTC cabs are limited in the number of subscriber lines they can take (shy of 300, I think), I'm not aware of reports of them becoming full yet and I suspect take up is not that great generally.
2. FTTC may be linked to a nearby not your ADSL current exchange, which is going to be on the 21CN network.
I think the combination of these reduces the likelihood of contention issues to the extent experienced with ADSL.

From my local experience near end crosstalk (from the Cab) is the bugbear, but the Fritz! Impulse Noise Protection (which seems to be "on" the download - but not on upload) with BT's Broadcom chips reduces CRC errors substantially. (Though I believe it also increases FEC errors substantially too which is a sign it's doing its job?). Probably only an issue though for longer lines. As to throughput speeds I don't see any evidence of a "peak" slowdown.

[Lance]

FECs are an indication that interleaving is applied to the line.

[Ardua]

Thanks guys. As my FTTC cabinet RFS date has just moved back by 3 months, I am just trying to get a feel whether a 17Mbps ADSL2+ connection will serve me better than FTTC? My FTTC estimate is 37Mbps and I note from a TBB forum that the estimate is supposed to include crosstalk degradation. There is also reference made to an OR document which suggests that the initial choice of the 8c profile was based to some extent on crosstalk considerations - primarily to protect ADSL2+ users. I am now very much out of my depth!

[Steve]

My short experience of FTTC suggests that the 'speed' is there and ever present. If I was an avid gamer I would be less than happy as latency is variable and on my install no better than adslmax. (I never had the option of adsl2+)