Re: Low latency communication over wifi

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > (I could use Intel 3945ABG-based card instead, but I figured out 
> > ath5k might be easier to hack?)
> > 
> > Is there way to manipulate type of service from userland to get
> > similar behaviour without patching kernel?
> 
> If your AP has WMM/QoS then you can use setsockopt(SO_PRIORITY) to
> change the TID and thus the AC and get your packets classified as voice
> (VO) on wifi, which makes them much more likely to get access to the
> medium.

That would be equivalent to ping -Q, right? It does not seem to have
any effect :-(. I'd expect at least local machine to use shorter waits
for medium, and thus drop packets instead of waiting.

On Wed 2015-09-23 13:42:36, Bastian Bittorf wrote:
> * Pavel Machek <pavel@ucw.cz> [23.09.2015 13:38]:
> > Is there way to manipulate type of service from userland to get
> > similar behaviour without patching kernel?
> 
> yes, iptables DSCP / DiffServ / Differentiated Services Field
> 
> # you have to add some magic for matching your data
> e.g. $IPT -t mangle -I OUTPUT -j DSCP --set-dscp-class CS7

Again, this is ping -Q equivalent, right? I was doing

ping -c 300 -i .2 -Q $[56*4] -s 500 amd
300 packets transmitted, 300 received, 0% packet loss, time 60989ms
rtt min/avg/max/mdev = 2.155/8.599/44.475/5.677 ms
300 packets transmitted, 300 received, +1 duplicates, 0% packet loss, time 61030ms
rtt min/avg/max/mdev = 2.158/23.809/300.956/49.969 ms, pipe 2

I would expect packet loss, but got long delays instead.

> also you should consider force the ACK-timing to 450m / Class1
> and forbid retransmission in minstrel

Yes, disabling retransmission would be useful. How would I do that?

Thanks and best regards,

									Pavel
-- 
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