> There are huge savings in only buying enough bandwidth to handle, say, your 95% load and not enough to satisfy all of your customers at once.

It's bad engineering to run your links hot at 95%. (Here's looking at you, Comcast)

You want to keep link usage at under 50% in order to have adequate margin for growth, be able to fall over to your secondary links without saturating them for maintenance/repairs/emergencies and handle microbursts which don't show up on the 5 minute average timescales monitoring is done at.

By that, I meant 95th percentile. That's the number you'd usually add your safety padding to.

My bad, I misread your point, but in hindsight it's quite obvious what you meant from the context. Wording was a bit ambiguous tho.

I knew what I meant, darn it! :-D

Part of the problem is adding capacity in an HFC network is expensive and difficult, eventually adding more carriers is not enough, and you needs to break the broadcast domain down even further, which means adding a new node - sometimes that can be just adding cards to a cabinet, others its a new physical box that must be permitted and placed - a process that can (and often does) take years.

xDSL has it easy, they can just turn up more backhaul at the CO, which is often a process that takes no more that days, if not hours.

> Part of the problem is adding capacity in an HFC network is expensive and difficult

Sure, but no more than doing VDSL, which is basically the same thing for ADSL as splitting nodes in a HFC network. A FTTC+VDSL upgrade is about $400 per subscriber which is $17 per month on a typical 24 month contract. That's quite doable and typical network life cycles are much longer, which brings the cost further down.

I don't fully agree.

When you build out VDSL, you're expecting to provide service to every customer in range at a fixed oversell ratio, if you need more bandwidth you can turn up additional fibers to the node, at the worst, split the mux down to smaller numbers of subs per, but the aggregation point never changes - it's always at the RSLAM.

With cable, the point of aggregation is at the subscriber prem, just like thinnet - the only way to get more bandwidth to the subscriber is to decrease the size of the broadcast domain by adding another node.

It's basically my contention that like most wireless networks the pinch point is access layer, not in the backhaul, HFC networks are much like wireless networks, they have a fixed amount of RF bandwidth shared with N subscribers over a given area - being that the amount of spectrum a given area can use is fixed (by licensing or by bandwidth limitations in the cable) the only way to handle more subscribers in a given area is to decrease the number of subscribers per network element, in short, add more sites, or nodes.