Originally Posted by dub45
Surely contention rates are an important feature of any commercial bb product and should be on the record just as much as the speed of the product or the cost?
Yes... but I would argue that in a properly managed network it should not concern the consumer.
For example UPC have 135,000 broadband subscribers. Say they all took 10Mbit packages, that's 1,135,000 mbits, or 1135 Gbits, 1.135 Terabits of internet connectivity required.
Obviously they don't have 1135Gbits - that's contention, but so long as it is far enough up the access network it's not a problem in itself. Average internet usage is probably only about a couple percent of sold capacity.
Where the problem comes is in a local exchange for DSL, or at node level with DOCSIS. Say you plan on 2% usage at national level. So for every 1000 gbits sold, you have 20 gbits available. That (or something in its range) is absolutely fine and transparent to the end user. But it's a contention ratio of 50:1. It works because of the thousands of people who don't use their connections some days, who only browse on a 10Mbit connection etc. etc.
However consider the DSLAM in the exchange that has 24 10Mbit connections on it. Total demand 240Mbits, but what if you only gave it 10Mbits connectivity? That's only a 24:1 contention ratio, twice as good
as the 50:1 you plan with nationally, but it's ridiculously low. It means that if any of those 23 other people use their internet at all, you don't get the advertised speed - so you can't really go any worse than 10:1 at DSLAM level.
So the closer you get to the consumer, the less you can contend the network. The same happens in power distribution networks... consider that there are some 1.3 million households in the state (before you consider commercial demand) and each with a maximum import capacity of around 16kVA, which at unity power factor is 70A. Say for conservatism that everyone's fused at 60A (you can see this main fuse in your own ESB cutout).... and that's 1.3million x 60 x 230 = 17.94 Gigawatts.
The maximum available capacity to Eirgrid on any given day is around 6GW - less than a third of the maximum demand available to domestic installations.
Electricians call this diversity, comms engineers call it contention. We don't have blackouts every night at 10pm, because diversity is well managed in the power network. Why do we tolerate poorly managed contention in broadband?