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Indeed - to get maximum performance with WiFi you must form large
aggregates. They are limited to 5.3ms of data, which is a
theoretical 4MBytes of data for 11ac radios. (8x8, MCS9). In
practice, today it's very rare to see > 3x3 and MCS8 or 9, so
somewhere between 1.5 and 2MBytes of data in an aggregate. You need
sufficient queues to form these aggregates, or performance is very
poor.<br>
<br>
Simon<br>
<br>
<div class="moz-cite-prefix">On 7/31/2015 10:04 AM, Jonathan Morton
wrote:<br>
</div>
<blockquote
cite="mid:CAJq5cE1CmHjhkmG-_c3yLEX-uViTMk7OVf9trS+gEB6Djpw4gQ@mail.gmail.com"
type="cite">
<p dir="ltr">> I think that is achievable, *even if there is a
WiFi network in the middle*, by thinking about the fact that the
shared airwaves in a WiFi network behaves like a single link, so
all the queues on individual stations are really *one queue*,
and that the optimal behavior of that link will be achieved if
there is at most one packet queued at a time.</p>
<p dir="ltr">I agree that queues should be kept short in general.
However I don't think single packet queues are achievable in the
general case.</p>
<p dir="ltr">The general case includes Wi-Fi networks, whose TXOP
overhead is so ruinously heavy that sending single MTU sized
packets is inefficient. Aggregating multiple packets into one
TXOP requires those several packets to be present in the buffer
at that moment.</p>
<p dir="ltr">The general case includes links which vary in
throughput frequently, perhaps on shorter timescales than an
RTT, so either packets must be buffered or capacity is left
unused. This also happens to include Wi-Fi, but could easily
include a standard wired link whose competing load varies.</p>
<p dir="ltr">The endpoints do not have and do not receive
sufficient information in sufficient time to reliably make
packets arrive at nodes just in time to be transmitted. Not even
with ECN, not even with the wet dreams of the DCTCP folks, and
not even with ELR (though ELR should be able to make it happen
under steady conditions, there are still transient conditions in
the general case).</p>
<p dir="ltr"> - Jonathan Morton<br>
</p>
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