[Bloat] benefits of ack filtering

Mikael Abrahamsson swmike at swm.pp.se
Wed Dec 13 04:46:00 EST 2017

On Wed, 13 Dec 2017, Jonathan Morton wrote:

> the uplink shaper is set to about a fiftieth of that.  I seriously doubt 
> that DOCSIS is ever inherently that asymmetric.

Well, the products are, because that's what the operators seems to want, 
probably also because that's what the customers demand.

So my modem has 16x4 (16 downstream channels and 4 upstream channels), 
meaning built into the hardware, I have 1/4 split.

Then providers typically (this is my understanding, I haven't worked 
professionally with DOCSIS networks) do is they have 24 downstream 
channels and 4 upstream channels. Older modems can have 8 downstream and 4 
upstream for instance, so they'll "tune" to the amount of channels they 
can, and then there is an on-demand scheduler that handles upstream and 
downstream traffic.

So I guess theoretically the operator could (if large enough) make a hw 
vendor create a 16x16 modem and have 32 channels total. But nobody does 
that, because that doesn't sell as well as having more downstream (because 
people don't seem to care about upstream). It just makes more market sense 
to sell these asymmetric services, because typically people are eyeballs 
and they don't need a lot of upstream bw (or think they need it).

On the ADSL side, I have seen 28/3 (28 down, 3 up) for annex-M with 
proprietary extensions. The fastest symmetric I have seen is 4.6/4.6. So 
if you as an operator can choose between selling a 28/3 or 4.6/4.6 
service, what will you do? To consumers, it's 28/3 all day.

So people can blame the ISPs all day long, but there is still (as you 
stated) physical limitations on capacity on RF spectrum in air/copper, and 
you need to handle this reality somehow. If a lot of power is used 
upstream then you'll get worse SNR for the downstream, meaning less 
capacity overall. Symmetric access capacity costs real money and results 
in less overall capacity unless it's on point to point fiber.

Mikael Abrahamsson    email: swmike at swm.pp.se

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