[Cerowrt-devel] Recording RF management info _and_ associated traffic?

Richard Smith smithbone at gmail.com
Thu Jan 22 13:19:51 EST 2015

On 01/22/2015 04:18 AM, David Lang wrote:

>> Recently, we picked up the 11th floor as well and moved many people up
>> there. I got a 3rd AP (another TP-Link AC1750) and set that one up on
>> a free channel with a different ESSID.
> I like to put all the APs on the same ESSID so that people can roam
> between them. This requires that the APs act as bridges to a dedicated
> common network, not as routers.

That's the ultimate plan but for convenience of being able to easily 
select what AP I'm talking to or to be able to tell folks to move from 
one to another I've got them on different ESSIDs.  It also helps me keep 
track of what RF channel things are on.

>> Then about a week before my original post I got notified that Internet
>> was down.  Both 10th floor APs had stopped working.  The 11th floor
>> (where I am) was still working.   On the 10th floor, I could connect
>> to the  TP-link via its IP address on its wired interface but it did
>> not seem to be passing wireless traffic. A reboot fixed it.
> There has been an ongoing bug with Apple devices on 5Ghz that causes the
> wifi chipset to lockup. We think we've fixed it in the current Cerowrt,
> but I don't know what kernel versions have this problem. This is likely
> to affect multiple vendors who use the same chipset (check the openwrt
> hardware list for details of the chipsets in each model)

Oooohhh!  That could be it. We have a _lot_ of Apple devices.  Most of 
the company uses MacBook,or Air and a large number of people have 
iPhones and we use iPods for some of our testing.   I'll go dig through 
the openWRT and get the details.

>> The WNDR3700 was completely unresponsive both via WiFi and when I
>> tried its IP connected directly to it's switch with a Cat-5.  I also
>> have a serial port mod on that wndr3700 so I connected up to that
>> instead.
> hmm, it's not common to have it be unresponsive on the wired network.

It's uncommon to me. :)  This unit has travelled with me for years while 
I worked for OLPC and its see a lot of different wireless environments. 
   Granted never one with this many apple clients.  Usually 7-8 
Linux/Windows machines and a pile of XOs.

So this happened a lot at your SCALE setups?

>> room. All the stations are in about a 40 foot radius and all but 1 or
>> 2 have line of sight to the AP.  The wndr3700 is in a closet on the
>> side of the room with other equipment so it might be 80 feet away from
>> the furthest station or so.
> this doesn't sound unreasonable unless your users are trying to use a
> LOT of bandwidth (although the fact that you refer to the 50Mb
> bottleneck indicates that you may be)

The bottleneck was just a nice side effect.  We don't use that much 
traffic.  I only noticed the limit once I started running 
netperf-wrapper tests from a wired host.

Occasional there will be some big download that eats up bandwidth, but 
when I watch the throughput during the day we peak up in to the 40Mbps 
but the average is < 10Mbps (Download).

>> Can I perhaps approximate signal strength by looking at the bitrate
>> for packets that station sends?  The theory being that higher quality
>> RF links should use the higher bitrate encodings when sending.
> not reliably, too many other things factor in to that.

Indeed. Horst tells me I basically have 2 rates happening on the tplink 
6Mbs and 24Mbps with a few 12Mbps in there.

>> If need be I can move the wndr to the same location as the tplink and
>> then have stations connect to the wndr so I can watch the rx signal
>> strength.

Looks like that's what I'll have to do.

> There is a lot of room with consumer grade equipment from where you
> currently are. The "Enterprise Grade" systems do have a lot of
> infrastructure to coordinate the different APs.

Thanks for the ray of hope.  Yeah I don't need all the multi-AP 
coordination handoff stuff.

Richard A. Smith

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