[martinald]

Actually most of the capacity problems on cable networks come from upstream congestion; not downstream congestion and this has nearly always been the case. When the upstream gets congested TCP ACKs get dropped and it kills download speed.

Upstream has always been challenging on coax. The first cable modems didn't even use the coax for upstream, instead it used a separate dial up modem.

I'm not entirely sure of the details but even after that DOCSIS has always had to use much lower frequency channels for upstream which are much more limited vs downstream which tends to use higher frequencies. Potentially because it was hard to get high frequency transmitting upstream low cost CPE devices back in the day?

[throwawaaarrgh]

It's about prioritizing downstream since that's 90% of the traffic and what customers complain about the most. No normal customer complains about their upstream cap, but they will freak out over congestion or not having the fastest download speeds

[virtuallynathan]

I didn’t generally see upstream congestion when I worked on Internet QoE at Comcast, downstream was more common. Cable modems do ACK suppression as well to help there.

[whaleofatw2022]

That, also the relatively low frequency range was originally only there for the sake of public access and the like; they only expected a relatively small number of channels on the return path.