[Bloat] benefits of ack filtering

Sebastian Moeller moeller0 at gmx.de
Wed Dec 13 07:36:09 EST 2017

Hi Mikael,

> On Dec 13, 2017, at 10:46, Mikael Abrahamsson <swmike at swm.pp.se> wrote:
> 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.

	Not 100% about the demand; I believe this also has a component of market segmentation:
a) everybody that actually wants to offer content is going to be not to well-served with the asymmetric links and hence might need to upgrade to the typical business-grade contracts that AFAIKT often have smaller download/upload ratios.
b) I seem to recall (but can find no evidence, so I might fantasizing) that having assymmetric traffic can have advantages for an ISP with peering/transit costs.

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

	In addition to the differences in available modulations for down- and upstream channels.

> 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).

	Or because more symmetric offers can be sold for more money to businesses (sure the "business" contract class probably offers more than that, but I think this is one thing it does offer).

> 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).

	Let's put it that way, people simply do not know as in the advertisements one typically only sees the downstream numbers with the upstream relegated to the footnotes (or hidden behind a link). If customers truly would not care ISPs could afford to be more open with the upstream numbers (something regulators would certainly prefer to hiding the information in the fine print).

> 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.

	I agree that most users would see it that way (especially since 4.6 to 3 is not that much loss); also I b;eive it will be hard to offer simultaneous 23/3 and 4.6/4.6 over the same trunk line (not sure whether that is the correct word, I mean the thick copper cable "tree" that starts from the CO/gf-attached DSLAM).
	For ADSL the challenge is that the up-/downstrewam bands need to be equal for all users on a trunk cable other wise interference/cross talk will be bad; and the most remote customer will still need some downstream effectively limiting the high end for the single upstream band in ADSL. VDSL2 sidesteps this issue somewhat by using multiple upstream bands and more remote lines will simply miss out on the higher frequency upstream bands but will still get a better symmetry...

> 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,

	These limitations might or might not be close: https://www.assia-inc.com/wp-content/uploads/2017/05/TDSL-presentation.pdf

> 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.

Best Regards
> -- 
> Mikael Abrahamsson    email: swmike at swm.pp.se
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