Meet DOCSIS: the unsung hero of high-speed cable Internet access | Hacker News Reader

Meet DOCSIS: the unsung hero of high-speed cable Internet access

arstechnica.com

58 pointsvkdelta11 comments

When I read this, it brought back memories of being back in '98 or so, when I got the first cable modem Charter had to offer. It came in the form of an ISA card that used my existing dialup modem for the upstream and the cable for the downstream, and I'm pretty sure was not DOCSIS compliant as the cable co had to swap all the things out a year later.

It only supported Windows 98 (barely), no NT and definitely no Linux. When it worked though it certainly was fast, but was weird having 10 Mbps down and 33.6Kbps up.

So three cheers for DOCSIS and 2-way cable plants!

I have 20 / 2 cable at home up from 10 / 1. Using DOCSIS 3.0. I finally don't care about getting anything faster, in the near future.

We actually just got 55 Mbps down / 5 Mbps up from DOCSIS 3.0. I can't imagine needing anything faster in the future, but I'm sure in 10 years I'll think it's slow as molasses.

Luckily DOCSIS3 scales pretty well. You can just keep adding bonded channels. 4 or 8 channel D3 modems are common these days but we have 16 and 32 channel models waiting in the wings. Since cable systems aren't exactly symmetrical from a spectrum standpoint the upstream speeds will continue to lag a bit but 25-50Mbit/sec is do-able today. 50-100Mbit will probably be common in 5 years.

I'm curious about why the artificial limit? The cable cos have enough backbone bandwidth, right? So why can't they just add channels and sell 100mbps+ today?

Some companies do offer 100Mbit packages today however it's mostly a gimmick. They would face a much bigger challenge/cost to offer every single customer 100Mbit. There's a surprising lack of demand for customers who are willing to pay more for faster speeds. It seems the $50 or less per month price point is what people want.

Crazy blast from the past. I worked on a cable modem project as my first job out of college in 1999. Back then, having a USB interface on the modem was a huge thing because it meant the cable company didn't have to open a customer's computer to install an ethernet card (and deal with the customer's complaints afterward that their computer didn't work anymore). Nearly everyone was using dial-up then, so most computers didn't come with ethernet.

"This makes it possible to use the same TV channels for cable that are also used for broadcast over the air" -- can someone explain what this means?

I think it means that the cable carries an analog TV signal at the same frequencies used by over-the-air broadcasts. If the cable wasn't shielded, it would act like an antenna and pick up radio-broadcast signals. That would cause interference with the cable signal. But since the shielding electromagnetically isolates the cable, cables and over-the-air broadcasting can use the same frequencies.

Hmm TDMA for upstream seems wasteful, imagine all those unused slots.

In the world of netflix and Youtube, We dont see those unused slots. Almost every other slot has user data (except DOCSIS maintenance messages). Only other option is SCDMA which is not widely supported on the CMTS platforms (cable routers) and has many other issues attached to it. So, right now A-TDMA is our best bet.

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