where the flamingcow roams

Cable modem channel party

There’s been some hype lately about cable providers forcing modem upgrades. If you’re subject to the DOCSIS 2 retirement, get a new modem, please; you’re hurting everyone else by forcing your provider to keep DOCSIS 2 enabled. Angry that you’re renting a modem and your provider is charging you anyway? That sucks; you should stop renting.

Which new modem? And what if you’re already DOCSIS 3; does upgrading help? There are lots of sites out there that will answer this question in terms of maximum throughput for a given number of channels. Wikipedia has a handy chart, and Comcast has a device browser. So, get a modem that has at least enough channels to support your capped speed.

But is anything beyond that worth it? Your cable provider can balance traffic across your connected channels. It can presumably also move you to another set of channels, though presumably that’s disruptive so not often done. The classic problem in cable networks is service degradation due to competition with neighbors: you’ve got someone on the same physical circuit as you with a high speed cap, a torrent client, and a compulsive collecting problem, and you’re in trouble. Cable circuits are oversubscribed enough that you realistically have to share channels with others.

This adds up to mean that having a cable modem that supports more channels is a win, even if your speed cap is much lower; you’re more likely to have channels that aren’t saturated. Interestingly, it’s also a benefit to you if your torrenting neighbor connects on more channels. In fact, modulo limits on the number of clients per channel, the efficiency of the whole system increases the more channels everyone is connected on.

Of course, none of this solves fundamental circuit oversubscription. Ubiquitous speed testing has put some social pressure on ISPs, but until the US fixes its horrible telco/cable/cell monopoly systems, those problems are unlikely to be really solved.

Also note that all of the modems use 4 channels for uplink. Upload speeds don’t play into this discussion.

Common modems, in case you’re persuaded: