There is no provider network (or even non-trivial corporate network) without over-subscription somewhere. It is completely impractical to achieve. Consider a

There is no provider network (or even non-trivial corporate network) without over-subscription somewhere. It is completely impractical to achieve. Consider a simple Ethernet network with 4 nodes each with a 10gbps connection: A B # C D Assume the switch in the middle (the "#") is a non-blocking cross-bar switch, so every port has a dedicated internal 10gbps path to every other port. Even in this simple example, you already have over-subscription which cannot be resolved except by having every node directly connected to every other node: while each node can transmit (and receive) 10gbps independently, if, say, nodes A and B both want to transmit 10gbps towards node C, the egress buffer for port C on the switch will fill up and overflow. Ok, you say, I'm just worried about ISP networks, not some free-for-all hypothetical Ethernet network where the nodes want to talk to each other. All the subscriber nodes just want to talk to the uplink, not each other: ----+ 100 gbps uplink +---- | DSLAM or similar device | ----+-+-+-+-+-+-+-+-+-+---- | | | | | | | | | | A B C D E F G H I J ... Here we have a (practically speaking) non-blocking node. But, ISPs need to have way more than 100 subscribers to be practical. So we need a lot of these devices. And we've just moved our contention up a level or two: [ uplink switch ] + + + + + + [ DSLAM ] [ DSLAM ] [ DSLAM ] [ DSLAM ] [ DSLAM ] [ DSLAM ] ... If we have 10 of these DSLAMs connected to an uplink (still quite small for an ISP in a moderate-sized town,) we need 1tbps of bandwidth going to our core router. If we have 100, 10tbps, and so on. From there, at a typical big ISP, you'd have connections going toward (directly, or via another intermediate location) two different exchange points. And there, the math, which is already completely implausible, becomes totally bonkers. The reason being that a typical ISP wants to do what's called settlement-free peering to exchange traffic with other providers, rather than buy connectivity from one or more of them. So, to keep our network "oversubscription free", whatever max uplink (likely in the thousands of terabits per second range at this point, at the very least,) has to be provisioned with every single provider our hypothetical ISP peers with. After all, we aren't doing any statistical traffic analysis. We're just making sure that there is no point of contention between any of our customers and any provider we peer with, anywhere in our network. Even if you take peering out of the equation, all you've done is move the problem around: a provider could buy, say, 10,000 tbps of bandwidth from another provider, I guess, but then that provider which is peering with hundreds of other ISPs has the same problem. Otherwise, its just a shell game where provider A says "we don't oversubscribe" knowing full well their upstream provider does. This is all completely insane. Nobody does it. What good operators do, instead, is proactively monitor their network and add capacity as needed, preferably before anything gets saturated.