[Cerowrt-devel] Managed to break 802.11n (on a 3800)

[Sebastian Moeller]

Hi Aaron,


On Jan 16, 2014, at 20:08 , Aaron Wood <woody77 at gmail.com> wrote:

> 
>>> Sebastian, after sorting out the router, it's still biased, but far
>>> less
>>> so, about a 2:1 ratio between upload and download.
>> 
>> So I See offen 10:1 and worse @165Mbit/s raw wireless rate
> 
> I get mixed results, but they aren't good.  

	I just checked again and I get crazy results for both RRUL and RRUL_NOCLASSIFICATION:


in both cases I get ~ 10:1 out-in imbalance. And even crazier just had one rrul where both in and out came up almost perfectly at 1:1. Interestingly the classification really works in giving different bandwidth for the different classes. (And in rrul_noclassification, where the still classified UDP probes make it through the EF flow gets shorter latencies…). 
	Note that measuring through cerowrt to a wired host (with too restrictive firewall settings) get:

with the MacBooks uplink still dominant (actually continually getting more bandwidth…). Since I my only wireless connected machines are macs and nobody else complained about this issue I assume it is an osx issue


For comparison an RRUL test from the wired linux host to cerowrt, where things look much better...



> IIRC, apple really changed something about the media access in 10.8, I'll look into that.  And see if my wife will let me install netperf on her laptop (I think it's still running 10.7)

	Yeah, good question whether this is the same in all macosx versions? (Sonner or later I will switch to 10.9 and repeat the measurements…) The saving grace is that I usually either upload or download at home between my 2 computers so I rarely feel the full force of this unfortunate macosx behavior. Just checked using SMB to copy a file to the wired machine and from the wired machine at the same time, nicely splits the bandwidth evenly between up and download, so this might be netsurf related...

> 
> 
>>> Also, my understanding was that with rts/cts, the router was in control
>>> of
>>> that aspect of things?  
>> 
>>     That is what I thought AS well, but it is not what I See with osx 10.8.
>> 
> 
> It may be a case of the station aggressively asking to send, and the AP granting instead of sending data to the station that's waiting.

	I think we agree that the AP should show more self-confidence and reject such requests more firmly :)


> 
> It should be clear in a monitor-mode tcpdump (or a statistical summary of packets).

	I am not really equipped to do this, with just one wireless notebook at my disposal :)

best
	Sebastian


> 
> --Aaron

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