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Roaming Problems in "industrial" Enviroment

Sebastian K

Hi all together,

 

A week ago we installed nine Sophos AP´s (AP100X/AP55C/AP55) for our 8 forklifts. The WiFi Signal is pretty good and the forklifters have Intel Wifi-Chipsets in their Industrial PCs (all brand new with FT Support) mountet in the drivercabin connected to the APs with a small external antenna. They work remotely on a Remote-Desktop-Server (win 2k8R2).

We experience a very poor roaming behaviour, with signal loss all few minutes. We managed it to get it work better by enabling the Fast Transition (FT) Option for the WLAN and increased the "Roaming Agressiveness" in the Client Driver Setting to "highest".

But we still get a lot of WPA failures (Code 2) and sometimes "WPA: received EAPOL-Key with invalid MIC" failures. The result is a connection retry every few minutes(successfull but annoying for the forklift Drivers ;)).

Fact is, the forklifters are very fast. Could it be that there is not enough time to roam? On the other Hand, we have Iphones or my Laptop (with connected RDP) on the same forklifter roaming much faster and more stable.

I made a Heatmap from the area to see, if there is enough overlapping wifi Signal spectrum. From my understanding ist should work fine, even if they are fast.

Has anyone ideas to improve the roaming behaviour or some best practices?

We had a 8 year old Cisco Enviroment before and hadn´t any Problems. But the AP´s had big Omni-Antennas which (we thought :)) could be replaced wirh more APs.

As I said, other devices seem to work just fine.

Thanks in advance and  a nice Weekend everyone.

 

Sebastian



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    Hey guys,
    I´d like to share my solution for the Problem mentioned above, just in case that someone else is running in similar Problems. I have only a basic understaning of WiFi technologies, so it´s just some points I learned and heard. But at least it´s working now. ;)


    Summary:
    We assume that our fork lifters leave the WiFi cell to fast, so the hand-over times are way too long to work in a good way. So we could extend the wifi ranges or speed up the roaming to solve the problem. We use the Sophos APs in an environment with much reflecting materials and wanted to go with small cells and faster roaming.
    The roaming issues were solved by an adequat WiFi Client, which has „special“ roaming options.
    We are using this Product: http://catalog.weidmueller.com/procat/Group.jsp;jsessionid=B38112C4E3CD805B8E82C9723D5CB7E9?page=Group&groupId=%28%22group3480584433217%22%29

    This is just an example and I think there are way more Products like this. I searched for "industrial wlan fast roaming" and found three products that fitted our needs. The one I mentioned was the first to arrive and solved everything we wanted.


    Here is the way behind us:
    At first I had to learn that roaming behaviour is completely controlled by the client and there are extremely different ways to "roam" or to handle this. I thought that a WIFI Module with roaming option is good enough to handle this… (maybe) but not in our AP Infrastructure setup.
    I found that a “normal” hand-over from an office wifi Client is between two and four seconds in our WLAN. Most of this hand-over time is channel searching by the client and then the normal 4 way hand-shake plus the whole encryption thing.
    There are different ways how clients handle these options e.g. new connection after connection loss / active scanning or passive scanning (We tested only three WIFI Adapter). Furthermore some clients are able to scan just on some channels (or on a channel table) to decrease the time for channel scanning. Then you can say when the client should roam. For example the hand-over starts if the signal quality is going under 50 dB and there is another AP with a signal strength over 40 dB.
    Assuming that you have a well fitted AP Infrastructure the only thing that can help you, are advanced roaming options on the client side. We dropped our roaming time from 3,5 sec. to 0,3 – 0,5 sec per hand-over with channel listing feature on the above mentioned WLAN Device and have nearly no signal losses anymore.
    Actually we´re still adjusting some antennas to get the best out of it.


    Here are some things we have done (maybe there are more things you can do):
    Infrastructure:
    1. Create (or better let an WLAN Expert create) a WLAN heatmap. For me the Ekahau HeatMapper Tool worked very good to get an overview where you can see the WLAN coverage. With this picture you can adjust the antenna direction / AP installation spots / other foreign SSIDs on the same channel etc.) Don´t miss to check the overlapping areas of your WiFi cells. Is there enough time for the client to roam and so on.
    2. Check the amount of WLAN SSIDs on your AP Radios (we had three at the beginning) to minimize your error-sources and to check the ressource usage by the single SSIDs
    3. Check the settings of the WLAN SSID and see if there is a difference after changes (find it in the wireless log)
     - Check the network name (length / special characters / try to keep it short and simple…)
     - Security Algorithm (TKIP & AES (compatible))
     - Fast transition ON / OFF
    - Make sure that you´ve checked your AP channel setup. You can create a pattern that you repeat for all APs (e.g. 1 /6 /12). Goal is that there is no overlapping channel of AP neighbours.

    4. … talk to guys who know the WiFi things better :D Our Sophos Partner checked our WLAN Setup but found nothing to fix. But you can be sure that this side is safe.


    If your AP structure is up and running, check the client side:
    1. Do you have roaming options in the advanced device setting, play around with that
    2. Check when the connection is lost or packets are lost with wireshark or the wireless Log in your UTM.
    3. Analyse the patterns you gathered. Is it a general problem? Is it just in a few areas? Could the problem be caused through jittering, reflections or something else? Does the client Antenna fit to the AP “WLAN Bubble”? And so on…
    4. … talk to guys who know the WiFi things better ;)

    Hope this is helpful to get an idea for your troubleshooting.

    Cheers

    Sebastian

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