[lxgr]

On a congested upstream, DOCSIS unfortunately seems to behave like this due to contention for and the insufficient granularity of upsteam transmission timeslots.

This effectively means that even if your share of the total upstream link of a network "collision domain" (shared coaxial medium really) is low (i.e you're using less than 1/n and accordingly should not be experiencing queueing in the modem), you might be seeing latency spikes due to having to compete and wait for transmission timeslots.

My local DOCSIS link is experiencing anything between 0 and 60 milliseconds of latency which I suspect is mostly due to this (since it's inversely correlated to upstream bandwith).