[lxgr]

This law does not apply to queueing as encountered in routers. It assumes unbounded queues and a poisson arrival process (i.e. a memoryless channel); both assumptions don't hold for packet routers and senders using congestion control (TCP or otherwise).

There is, however, a high chance of encountering buffer bloat if countermeasures are not taken at the chokepoint: https://en.wikipedia.org/wiki/Bufferbloat

Modern cable modems, for example, are required to implement such countermeasures. My ISP is at over 90% capacity and round trip times are still mostly reasonable. (Bandwidth is atrocious, of course.)

[drewbailey]

How do you monitor this? The 90% over capacity, would like to see where mine is at

[lxgr]

There might be a way using a cable TV receiver (see my other comment on this thread), but in my case, a sales rep of my ISP just told me on the phone.

[mikepurvis]

I have an older modem (DCM476) and it definitely doesn't have this or doesn't have it enabled. I have to use/tune queue management myself on the router side.

[lxgr]

Yes, it's mandatory only as of DOCSIS 3.1, and yours seems to be 3.0. (Supposedly it has been "backported" to 3.0, but that obviously would not apply to existing devices certified before that amendment to the spec.)