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Comment by brk | Hacker News Reader

Backbones are generally symmetric.

Without getting into super deep detail, on cable internet, there is a balance between spectrum allocated for Tv content, and internet bandwidth. The system will have a finite amount of spectrum available, which can be divided between TV content, downstream internet, and upstream internet.

Given that most peoples usage is mostly downloading, the CATV carriers allocate more spectrum/bandwidth to downloads vs uploads.

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Any reason why can’t those be allocated dynamically and switched between upload/download? So your connection is still not symmetric, but at least your 350Mbps download speed can suddenly turn into 350Mbps upload, or be roughly evenly split in half if you’re both uploading and downloading?

I was pretty sure fiber was bi-directional so you can always saturate the same fiber with all upload or download based on demand. Copper wire can't do this so they use most of their last mile copper for download since that is what most people use the most of.

Yeah but my point is why can’t it do the same as Wi-Fi (since technically coax is just radio anyway) and dynamically allocate bandwidth for upload or download depending on usage?

technically possible, would require a ton of upgrades to the infrastructure to support such a thing, and probably just not worth the investment for these companies right now.

1) The filters and amplifiers that split upstream/downstream/video are typically hardware, tuned for specific frequency bands.

2) The cable is a shared medium (like wifi) so it’s not just a matter of what you’re doing, but what everyone else is doing.

It possibly could be. It has been 15 years since I worked in the CATV market, so I'm not totally up to speed on the nuances of the latest platforms.

ADSL2+ uses frequency division duplexing (FDD), ~9:1 ratio (50/448 bins). DOCSIS up to 3.1 is also FDD. Typical EuroDOCSIS 3.0 modem deployments work in 8/4 (max 400/100 Mbit) or 16/8 (max 800/200 Mbit) channel configurations.

Finally 'full duplex' DOCSIS 3.1, renamed to 4.0, promises up to 10Gbps symmetric transfers thanks to echo cancellation (V.34 dialup modem says hi). Of course we barely switched to 3.1 and its unlikely cable networks will jump on the 4.0 bandwagon any time soon.

4:1 is a reasonable ratio for consumer connections, at least. I'm sitting here on a DOCSIS 3.0 modem but it's set up as 10:1. And going up a tier doesn't increase upload speed at all.

Also, most downloads can be cached through CDNs near the requester, while uploads can not.

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