[Cerowrt-devel] what stats do people want from conference wifi?

David Lang david at lang.hm
Sat Feb 7 21:02:55 EST 2015

In the next few days I'm going to be building the openwrt images to use at the 
SCaLE conference. I will have ~50 APs deployed supporting ~3k attendees. This 
will be running on WNDR3700v2 and WNDR3800 APs. Since I am compiling the 
firmware myself, I can add in patches to gather and log stats for things that 
are not normally reported

The wireless network architecture is:

separate ESSIDs for 2.4 vs 5.
each band gets bridged to a different VLAN
the APs are configured not to forward broadcast traffic from one wireless client 
to another on the same AP (although broadcast traffic from one AP probably goes 
out others after hitting the wire now that I think about it)
I have all logs from the APs sent to a central logserver
I have use rrdtool to catpture normal bandwith/cpu/etc stats
I also have rrdtool capture how many clients are connected to each ESSID every 

What else can I gather related to the wifi?

I think it would be useful if we could gather info along the lines of

amount of airtime used

how much latency is added to packets while waiting to transmit because it's hearing something else transmit?

amount of unused airtime available

average effective bit rate

percentage of time spent doing broadcasts (things required to operate at the 
lowest bit rate)

Part of the reason that I compile my own firmware images is that I completely 
disable connection tracking in the kernel (because clients may move from one AP 
to another in the middle of a connection it's a waste of cpu and memory to 
track), and as a result of these optimizations, there is actually quite a bit of 
CPU available. The boxes almost never hit 20% cpu utilization, so there's quite 
a bit available to gather other stats.

some of the stats I gather are in messages spit out by the kernel, others from 
scrips running on the box querying things in /proc or /sys, and others from 
watching logs and summarizing them once a minute. I even have a process that 
goes threough all the connection logs for the duration of the show and graph 
how many unique MAC addresses we've seen and a breakdown into the different 
vendor prefixes. If there's a way to get the data, I can support it.

If there are fq_codel stats that people would find interesting in this 
environment, I can gather those as well (both on the APs and on the Debian based 

David Lang

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