[Bloat] benefits of ack filtering

Jonathan Morton chromatix99 at gmail.com
Tue Dec 12 17:41:44 EST 2017

Actually, the cost argument goes the other way.  You need heavy DSP to
*receive* high bandwidths; sending it is much easier computationally.
Also, in aggregate a hundred cheap CPE boxes probably have more DSP
horsepower than the one head-end box serving them.

What the centralised head-end has an advantage in is transmit power, and
thus SNR.  This feeds into Shannon's equation and supports your argument
more directly.  In ADSL this is partly compensated for by assigning the
lower frequency carriers to the upload direction, since they have less loss
than high frequencies on a copper pair.

However, in the most extreme examples I've seen, the level of asymmetry has
little to do with the underlying link technology and more to do with how
the provisioning was arbitrarily set up.

Things like ADSL with an unrestricted downlink sync rate but uplink limited
to 128k.  Or DOCSIS with a huge headline bandwidth for downlink, and no
obvious mention (until you've paid for it, set it up and measured it) that
the uplink shaper is set to about a fiftieth of that.  I seriously doubt
that DOCSIS is ever inherently that asymmetric.

- Jonathan Morton
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