On Mon, 25 Aug 2014, Sebastian Moeller wrote:
Hi Michael,
On Aug 25, 2014, at 10:01 , Michael Welzl <mich...@ifi.uio.no> wrote:
[...]
This is a case where a local proxy server can actually make a big difference
to you. The connections between your mobile devices and the local proxy
server have a short RTT and so all timeouts can be nice and short, and then
the proxy deals with the long RTT connections out to the Internet.
Adding a proxy to these considerations only complicates them: it's a hard
enough trade-off when we just ask ourselves: how large should a buffer for
the sake of link layer retransmissions be? (which is closely related to the
question: how often should a link layer try to retransmit before giving up?)
That's what my emails were about. I suspect that we don't have a good answer
to even these questions, and I suspect that we'd better off having something
dynamic than fixed default values.
What about framing the retransmissions not in number but rather in time?
For example the maximum of either time to transmit a few (say 3?) packet at
the current data rate (or maybe one rate lower than current to allow
setoriating signal quality) or 20ms (pulled out of thin air, would need some
research). The first should make sure we actually retransmit to overcome
glitches, and the second should make sure that RTT does not increase to
dramatically. This basically assumes that for reasonable interactive traffic
we only have a given RTT budget and should make sure not to overspend ;)
Yep, just like BQL helped a lot on the wired side, because it's a good stand-in
for the time involved, we need to get the same concept through the wifi stack
and drivers.
David Lang
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