DAWN – Final Post

So did I achieve my aims with DAWN?


  1. Simple Installation
  2. All patches Upstream
  3. Configuration of the nodes should be simplified
  4. Visualize the information of the participating nodes
  5. Improve the controller functionality by adding mechanisms like a channel interference detection and other useful features

1 and 2:

Everything is upstream!
All hostapd patches are merged. I even added some patch that extending the hostapd ubus functionality.
The iwinfo patches are merged too. But actually the patch from the other guy was merged that contained my patch #1210.
You can now simply add the feed and compile DAWN.

3 and 4:

I added a luci app called luci-app-dawn, there you can configure the daemon. If you do this, the daemon configuration is send to all participating nodes. So you don’t have to change the config on every node.
Furthermore, you can see in the App all participating WiFi Clients in the network and the corresponding WiFi AP. Furthermore, you can see the Hearing Map for every Client.



So I’m still refactoring my code. Some code snippets are ugly. :/
I read stuff about 802.11k and 802.11v.
802.11v is very interesting for DAWN. It would allow DAWN a better handover for the clients. Instead of disassociating the client, the client can be guided to the next AP using a BSS Transition Management Request frame format.
This request can be sent by an AP or station (?) in response to a BSS Transition Managment Query frame or autonomously.

I want to send this request autonomously instead of disassociate clients if they support 802.11v.
For that I would set a the Disassociation Timer (the time after the AP disassicates the client if it’s not roaming to another AP) and add another AP as a candidate. Furthermore I should enable 802.11r for fast roaming…
If you want to play around with 802.11v you need a full hostapd installation and enable bss transition in the hostapd config.


The stations sends in the association frame if it supports bss transition when associating with an AP.
My plan is to extend the hostapd ubus call get_clients with the information like it’s already done with the 802.11k flags.
After this I need a new ubus call in which I build such a BSS Transition Management Request like it’s done in the neighbor reports ubus call.
I found a patch on a mailing list that adds a function to build such a bss transition frame in an easy way.


Sadly, it was never merged. 80211v implementation can be found in the hostapd.

Furthermore, I could use 802.11k for asking a client to report which APs he can see. This is a better approach as collecting all the probe entries. The hearing map is very problematic, because clients are not continuously scanning the background (or they don’t scan at all). Furthermore a client can move around. Typically questions are, how long such a probe entry can be seen as valid. If the time span a probe request is seen as valid is set to big and the clients moves around, he can not leave the AP although the RSSI is very bad. (and a bad rssi is the worst thing you can have!) A bad RSSI can trigger the internal client roaming algorithm and the client tries always to roam to another AP and gets denied because there is already a hearing map entry with a very good rssi. But this entry is not valid anymore, because the client moved very fast.

My Merged Pull Requests:

My Open Pull  Requests:

My Declined Pull Requests:

GSoC 2018 – DAWN a decentralized WiFi controller (2st update)

I still try to get my patches upstream.
For the libiwinfo patch I had to add the lua bindings. I never used lua so first I had to get comfortable with this. Additionally I wanted to add the channel utilization in the luci statistics app. But suddenly Luci is giving me a null pointer exception in the dev branch.

Additionally I tried to get comfortable with Luci for developing my own app.
Meanwhile another developer created nearly the same patch for iwinfo that add the survey data for the nl802.11 driver… This patch is still not accepted. The only difference is that it returns all survey data for all channels (like iw dev wlan0 survey dump)…
Furthermore, my pull request for the hostapd ubus bindings that add information about the ht and vht capabilities had to be rewritten. (https://github.com/openwrt/openwrt/pull/898). Again I have to wait for some feedback. While rewriting this patch, I had a new idea: If you subscribe to the hostapd via ubus and want to notify on the messages you have to activate it. It would be possible to add flags in the hostapd_ubus_bss to select what information should be published via the ubus bus. Before doing so, I want some feedback if this is a good idea.If somebody is interested why I am interested in the capabilities: I want to create a hearing map for every client. I’m building this hearing map using probe request messages. This probe request messages contain information like (rssi, capabilities, ht capabilities, vht capabilities, …). VHT give clients the opportunity to transfer up to 1,750 Gigabits (theoretical…) If you want to select some AP you should consider capabilities… In the normal hostapd configuration you can even set a flag that forbids 802.11b rates. If you are interested what happens if a 802.11b joins your network search for: WiFi performance anomaly. 🙂

Summarizing, I spent a lot of time waiting for feedback, debugging, modifying my patches or replying on the email lists. It is a bit frustrating.
The cool stuff was that I had my first pull request. 🙂 (it was just a typo ^^) But somebody took the time to fork my project and create a pull request. 😉
Furthermore, it is exam time and I have a lot of stuff to do for the university.

Actually I wanted to go on with more interesting stuff like connecting to the netifd demo to get more information.

Or to look at PLC. There is an interesting paper EMPoWER Hybrid Networks: Exploiting Multiple Paths over Wireless and ElectRical Mediums.


GSoC 2018 – DAWN a decentralized WiFi controller (1st update)

DAWN is using the ubus bindings of the hostapd. Ubus is a messaging system in OpenWrt to which processes can subscribe and publish information or services. The hostapd ubus bindings allow to collect probe-, auth- and assoc-requests. Furthermore, it is possible to deny these requests. Additionally, we can gather client information or deauthenticate clients.
I made my life easy by just extending the hostapd ubus calls with all information I need. I wanted to get these changes upstream but some of my pull request were rejected. I added the bssid, the essid and stuff like this to the hostapd notifications. The pull requests were rejected because I can gather these information through the netlink socket. The ubus bindings of the hostapd should only spread information that can not be gathered in other ways. Now I only have two pull requests left:

Already accepted pull requests:

Added channel survey data in libiwinfo

I had to made the decision, if I want to directly use nl80211 or some library. I already used libiwinfo to contentiously update the rssi of the connected clients. Furthermore, the libiwinfo library is often installed on OpenWrt devices. With the libiwinfo it was possible to gather the essid and the bssid of the WiFi interface. The only information I missed is the channel utilization. The channel utilization is a value between 0 and 255. It is a measure how much a channel is used and what capacity is left.
The channel utilization can be calculated:

Unfortunately, the needed information is not contained in the libiwinfo. So I extended the lib by the necessary information: https://github.com/PolynomialDivision/iwinfo/tree/feature/channel_util
There is some weird behavior of the ath10k driver that I tried to debug. The ath9k driver is working very smooth. If I try to obtain channel survey data without waiting a short time, the survey results become 0. Just waiting between 2 calls fixes the problem.
When I had to figure out how to contribute to the OpenWrt projects. (https://git.openwrt.org/project/iwinfo.git) This can be done via the mailing list. There is a nice tutorial how to send patches using git (https://burzalodowa.wordpress.com/2013/10/05/how-to-send-patches-with-git-send-email/) I’m still waiting that the patch will be merged.

Now I can calculate the channel utilization. Instead of always updating this value, the channel utilization should be averaged. (channel utilization value can be very dynamic)

That’s it. Now I had to rewrite the daemon to gather the informations from the libiwinfo.


I want to implement bootstrapping. If a router joins the decentralized controller, it should automatically get the configuration from one router of the decentralized group. Different solutions are possible. I could use scp, rsync to get a configuration from another node. I wanted a different solution. With uci (Unified Configuration Interface) you can configure daemons. I use uci to read my configuration into the daemon. My idea was to send the daemon configuration via the network as a string and use uci to configure the daemon configurations file. Unfortunately, I had some troubles with the uci lib. This approach is not finished.

Lesson Learned – Use calloc instead of malloc!

I spent a lot of time trying to fix some stupid mistake.
The ubus c-library has a function called ubus_add_subscriber which expects a ubus_subscriber. Everything was fine in my old implementation because I used a global variable. Now I wanted to add more subscriber using an array of pointers. What I did was:
struct ubus_subscriber *sub = malloc(sizeof(struct ubus_subscriber));
ubus_add_subscriber(ctx, sub);

This crashed all the time and I was very confused. Finally, a friend of mine said that I should try calloc. It worked! The function ubus_add_subscriber goes through the existing pointers in this struct if they are not null!
Lesson learned: Use calloc. 😉

Lesson Learned 2 – Read header file comments carefully if they exist!

If you use uci_lookup_ptr(ptr,”bla.@bla.bla=blavalue”,true) it will not work!
uci_lookup_ptr needs a string that can be edited and that is not constant! 😉

DAWN – A decentralized WiFi Controller

I’m Nick. I study Computer Engineering at the TU Berlin. It is my first time participating in Google Summer of Code. I am realizing a decentralized WiFi controller.

DAWN is the first decentralized WiFi controller for OpenWrt. The controller provides access to valuable information, e.g., all connected stations, their capabilities, and information about all participating nodes. Moreover, DAWN provides load balancing to increase the network performance by controlling the clients association.

What’s missing?
An important aspect of the controller is the simple installation. Everybody, even people with limited technical knowledge, should use this controller to increase their network performance at home. Until now, DAWN requires a special patched OpenWrt to run. So a user needs to compile his own image. The first thing I have to do is to bring the last patches upstream. Some of the patches were rejected and that is why I have to rewrite different functionality and create new pull requests. Furthermore, I have to extend the libiwinfo library to get all necessary informations from the OpenWrt system.
After this, the configuration of the nodes should be simplified. So far, the user has to configure all participating nodes individually. I want to implement some bootstrapping to automatically configure the participating routers.
After simplifying the installation and configuration, I want to visualize the information of the participating nodes with a graphical user interface.
The last step is to improve the controller functionality by adding mechanisms like a channel interference detection and other useful features. Moreover, this step contains to improve the load balancing.

In my next blog post, I will write about why some of my OpenWrt patches were rejected, how I have to extend the libiwinfo. However, if this steps are successful everybody will be able to simply install DAWN without the need to patch OpenWrt.