

Meet DOCSIS: the unsung hero of high-speed cable Internet access - vkdelta
http://arstechnica.com/business/news/2011/05/docsis-the-unsung-hero-of-high-speed-cable-internet-access.ars

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ben1040
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!

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staunch
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.

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silverlight
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.

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jsz0
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.

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aditya
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?

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jsz0
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.

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yelkeew
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.

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vinhboy
"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?

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elwin
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.

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

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vkdelta
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.

