802.11 Wireless Channel Planning…

I used to work with Motorola Canopy wireless gear back in the day. It was great ptmp wireless gear. The carrier to interference ratio on this gear was 3 dB, which meant that you could provide extremely reliable wireless links in high RF congested areas. Of course this was proprietary based equipment that didn’t come close to the contention based CDMA/CA 802.11 stuff. I was extremely spoiled when using the motorola canopy line. It just worked.

Why am I bringing up all this when talking about 802.11 wireless channel planning? Well it’s because of the preconceived notion that using all the 2.4Ghz 802.11 channels may be a good thing (including overlapping channels). At first, I though, just let the AP’s pick the best channel between 1-11 and that I would be good to go. Well that wasn’t the best solution as AP’s were selecting channels 1,3,4,7,10, etc. My thoughts were spurred on by this twitter discussion with wireless guru, Keith Parsons.

Me to Keith “What’s better, SNR of 20db between two AP’s on channel 1 or SNR of 20db between AP on channel 1 and AP on channel 3?”
Keith “I’d go with the two on the same channel, given a choice. At least they’d ‘Play Nice’ with each other rather than ACI fighting.”
Me to Keith “So is it CSMA/CA that works better at detection if interference is on same channel?”

Keith “It is the difference between how 802.11 deals with CCI vs ACI.”
Me “So based on CCA, you would rather detect noise and back off rather than face possible data corruption from ACI.?”

The last question wasn’t answered. Basically I needed to do my homework and I would suggest you do the same. Check out the following link:


In the above article Andrew really dives into understanding how CDMA/CA works. What I gathered what that wifi can use carrier sense techniques in order to back off in order to avoid possible frame corruption. Keith’s statement of “AP’s on the same channel will likely play nice with each other” will allow carrier sense to do its job.

Ok, so I started doing some more research which lead me to my safaribooks account and checking out a CWNA (certified wireless network administrator) study guide book. The book defines CCI as co-channel interference or “unnecessary medium contention overhead that occurs because all the AP’s are on the same channel.” (Coleman and Westcott) Basically you have wireless devices following the rules of CDMA/CA.

Now ACI is defined as adjacent channel interference and is what you get when you use channels that overlap with one another. The only non-overlapping channels in 2.4Ghz are 1,6,11. When Keith suggests that he would rather see two AP’s on the same channel instead of two using overlapping channels such as 1 and 3, it’s because the 1 and 3 will give you ACI. ACI will cause re-transmits due to corruption of frames. You will rather want CDMA/CA to work as it should instead of facing re-transmits due to corrupt frames.

Where did this lead me? Well, I turned off the AP’s auto channel feature and went back to only using channels 1, 6, and 11. I hard set the channels myself and performed a site survey. My goal was to try to maximize the SNR between any two AP’s that my client could see that were on the same channel. At the end of the day, I’m seeing better performance especially since we just doubled the number of access points we used to have. I had to also play around with the minimum basic rate and power output levels as well in order to achieve maximum optimization.

Here’s a busy, but healthy network using 1,6,11 (Shane, disregard my previous comments on your screenshot using only channels 1, 6, and 11) – Courtesy of Metageek Chanalyzer

Metageek wireless channel planning spectrum image

Healthy 2.4Ghz wireless channel planning. I’m working on 5Ghz as well. – Courtesy of Extreme Networks Oneview.

wireless channel planning

Wireless channel planning map


CWNA: Certified Wireless Network Administrator Official Study Guide: Exam PW0-105, 3rd Edition by David D. Coleman; David A. Westcott


Raspberry Pi network monitoring wifi Smokeping

I finally deployed my wireless raspberry pi network monitoring device at the edge of our wireless network. I installed the smokeping app on the raspberry pi with wheezy via apt-get. I already had a smokeping running on a Linux server, so I setup the raspberry pi to run smokeping in client mode.

Client mode allows the raspberry pi to pull the config from the smokeping server in order to know what tests to run. I setup some fping, DNS, and tcpping tests. This is a great way to test the client’s wireless experience (latency) on the other side of campus. I stuck the raspberry pi behind a bundle of cables to provide for additional attenuation to simulate a user in a worse case scenario. The AP was a few rooms away on a different floor as well. Here are some of the smokeping graphs:

raspberryPi Smokeping monitoring wifi latency

The line with the higher latency is the raspberry pi to google and the lower line is the latency from the smokeping server to google via fping in the picture above.

Here’s a longer term graph painted vi rrdtool by smokeping. There’s some packet loss going on over the wireless interface on the raspberry pi. I may have to move it to a better spot and see how the graphs look afterward. I also want to install iperf and maybe tshark as well.

RaspberryPi smokeping long term wifi latency

Here’s the command to get the raspberry pi running in client mode:

/usr/sbin/smokeping –master-url=http://yoursmokepingcgiurl.com/smokeping.cgi –cache-dir=/var/smokeping/ –shared-secret=/var/smokeping/secret.txt

I also had to modify the permissions in the /tmp/smokeping-ms/data/ folder on the server in order to allow the rrds to be modified by apache.

If you’re looking for a small free solution or larger scale paid solution, take a look at netbeez.net. I would recommend giving their NetBeez free tier model a try.


Extreme Networks Wireless AP3705i deployment

I’m working on deploying 96 wireless access points in our student dorm rooms. We originally started with an initial deployment of 40 wireless access points. We installed the original AP’s in the hallways, but had signal issues due to all the HVAC in the vertical walls. Hallway installation wasn’t the greatest idea to begin with, but at the time of the initial installation we had limited funding to run cables to every suite. In our new deployment, we required that contractors pull cables into certain suites. Each suite houses 4 rooms,so I decided to place an AP in every other room and staggered the AP’s from floor to floor. There wasn’t much HVAC or piping in the horizontal flooring above or below the rooms, so signal penetration worked a lot better between the floors.


For those of you asking why Enterasys (now Extreme Networks), well we’re already an Enterasys shop and house 2 enterasys 5110 wireless 10Gb capable controllers in our data center. Enterasys wireless also has a niche of now being able to push up to L4/QOS policies down to wireless users as they do on their wired gear. This makes redirecting blacklisted users through our NAC system a breeze.


I also decided to go with the Enterasys ap3705i, which is a 2×2 dual radio mimo wireless access point versus the 3×3 model. We ended up being able to double our AP count because the 3×3 radio was almost double in cost. We typically see around 65% of 1×1 MIMIO mobile devices, so higher AP density just ends up making more sense for us right now.


Meraki Wireless Cloud Managed Dashboard

A few months ago, I was able to acquire a Meraki MR12 AP. I deployed it at a facility that wanted to use airplay between a few iphones and ipads to an appleTV. I figured this would be a great test, as most of the devices would be using bandwidth intense applications. One of the cool features that Meraki has is the ability to detect up to layer 7 applications.

meraki dashboard applications

This graph makes it really easy to see which applications are being used the most. Now you may ask yourself, what can I do with this information, besides create nice graphs and charts for upper management? Well, now that you know what applications are being utilized, you can now create custom policies that can deny or allow certain applications. You can even block certain hostnames or domains. You can also create and apply different bandwidth rate limits based on user or application. Maybe Jonny is trying to stream his favorite you tube video and you have someone else on the same access point who’s trying to do a presentation via airplay. You can decide who gets the highest priority and bandwidth. I like this solution because its an all-in-one setup. You don’t need separate boxes to get the job done. You don’t need a wireless controller or a bandwidth shaper. Now I’m not saying that this is going to work for every solution. Sometimes there is a need for wireless controllers and standalone bandwidth management shapers, but for this type of deployment Meraki fits the bill.

Aerohive HiveManager Maps Tool

The aerohive HiveManager maps feature is pretty powerful. You start off by dropping your AP down on an aerial view map. This allows for exact geocode positioning. You can outline your building with a perimeter in order to get a good floor layout. After you have drawn your perimeter, you can start laying out walls, doors, windows, elevator shafts, and cubicles. Each item represents different amounts of attenuation. To my surprise, the receive signal strength on my wireless devices matched pretty close to the predicted signal strength of the aerohive map. For instance, I was getting a weak signal in the outer N.E. room. I have a brick fireplace that’s in the corner of the room that’s next to the outer N.E. room. I drew that brick wall in the map and now you can see why I have a weak signal back there. The brick fireplace definitively impacts signal strength.



The map feature lets you set the minimum db rate. I have mine set to -80 and the strongest value is -35. You can also change what view you would like to see from the AP. I have mine set to Channel/Power view. You can also change it to hostname, node ID, IP address, or client count. Client count would be nice to see where your AP’s may be saturated with users in a large environment. Overall I’m pretty impressed with the areohive HiveManager maps tool.

Aerohive Wireless Review

I’m finally at a point where I can share my experience with the aerohive AP121 dual radio access point I acquired. When I first received the access point I placed it in my office which is in the northeast corner of my 1600 square foot ranch home. Unfortunately I wasn’t able to test the AP with all of my mobile devices because I wasn’t able to receive a strong enough signal on the other site of the house. I was only picking up at best a receive signal strenght of -78 to -80. This wasn’t good. The connection on my nexus 4, apple first gen IPad, and galaxy S3 would lag and drop connection constantly. I was using a dd-wrt extender AP in my living room which is in the center of my house prior to the aerohive AP. This type of signal penetration is to be expected when you’re working with mobile devices and with an AP that can only pump out a max of 20dbm.

I wanted to get the aerohive AP into the center of the house, so I picked up a pair of netgear powerline 200’s. This worked perfectly. I really wanted to dig into the aerohive cloud based dashboard, “hiveManager” with some client stats and placing the AP in the center of the house allowed all my devices to stay connected without a hitch.

I couldn’t help it. The first place I went to was the spectrum analysis utility.


This is a real-time spectrum analysis using the 2.4 Ghz radio. You get a nice waterfall view as well. The time it takes to refresh is instantaneous and this is going through their online cloud management system over a Comcast connection. I was able to test the speed by firing my dd-wrt repeater up in AP mode on channel 6. I instantly started to see the interference on channel 6. You also can see an FFT duty cycle graph as well, but I left that out on the screen shot.

Here’s another article on the Aerohive Hivemanager maps tool

Meraki Wireless MR12 AP

Here are some pics of the Cisco Meraki MR12.

meraki-2.4Ghz-AP MR12AP

Quick rundown on the MR12 single radio AP spec’s:

1 – 802.11 b/g/n 2×2 mimo radio

1 – 10/100/1000 Ethernet POE plus another 10/100 Ethernet

Internal 3dBi omni-directional antennas

Built in spectrum analyzer


Wireless Review

We are currently working on increasing AP density at work in order to keep up with the increasing amount of wireless client devices. It’s always nice to revisit what other product vendors have available, so I was able to get my hands on a few test AP’s.


I will be unboxing and testing these at home. They are lower end AP’s, but this will give me an opportunity at looking into the config user interface. Stay tuned!

Metageek at Interop


Metageek makes great wireless analyzer tools. The picture above is showing “Chanalyzer Pro”. The software works with Metageek’s Wi-spy usb wireless adapter line. The unique part about this software  is the ability to show all devices that may be operating in the 2.4Ghz spectrum. That means you will be able to identify noise coming from microwave ovens to 2.4Ghz cordless phones. Another cool feature is being able to see if the 2.4Ghz spectrum is overloaded. For instance if you have a high density AP deployment, you will be able to detect if your over saturating the 2.4Ghz spectrum. If so, you may want to consider lowering your AP’s power output. They also sell an adapter that can view the 5Ghz spectrum as well.


Interop wifi – so so


Wireless is a bust, at least in the conference room I’m in. The 2.4Ghz spectrum is saturated with hotel AP’s, mifi’s, and Interop wifi sponsor Xirrus AP’s.

I then turned my nexus 4 to strictly use 5Ghz (knowing that there is much more

channel space available in 5Ghz band), however Xirrus doesn’t have good 5Ghz coverage in the conference room I’m in. I was able to connect my macbook pro to a 5Ghz channel. Signal shows a -72db.

The more the 2.4Ghz band is saturated, 5Ghz will become even more important. As we move up the spectrum, our coverage range falls. Building out your wireless network coverage in 5Ghz is extremely important. If you know your 5Ghz coverage is great, then you already know your 2.4Ghz coverage will be more than adequate.

A great tool to use on OSx in the command line is:

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/A/Resources/airport -I

Running the command without any switches will show you all the available options.