In an earlier answer about broadband speeds (March 20), there was no mention of contention ratios. I can get download speeds of 8Mbps from BT; however, at busy times this drops to less than 2Mbps. My assumption is that there is insufficient capacity at the exchange to meet the demand from a number of users simultaneously. Derek Waters
The broadband capacity at the telephone exchange is shared between many different users, on the assumption that they won't all want to use it at once. Usually there are 50 home users per stream, or 20 business users, with the business users paying the extra cost. The contention ratios are therefore 50:1 and 20:1.
However, while you might be on a congested exchange, I don't think it's contention in this case. In the evenings, BT and some other ISPs use traffic-shaping, or throttling techniques to limit bandwidth so that everybody gets a share. I expect your 2Mbps is a consistent rate and that your connection goes back to 8Mbps instantly at midnight, or whenever the ISP turns traffic-shaping off.
The problem is that a relatively small number of peer-to-peer file-sharers are using the majority of the communal bandwidth. It's a bit like leaving your taps turned on all the time, except P2P software adds lots of extra taps. Some people now want to change the net's so-called fairness algorithm to stop file-sharers taking more than their share. See Flow Rate Fairness: Dismantling a Religion, written by a BT researcher.
