Wireless Access

Hi, we have an MSM760 with multiple MSM460 and MSM466 Access Points. No Mobility license.

The warehouse VSC is using WPA/WPA2-PSK. Investigating user complaints, we found that devices never roam to a stronger AP as long as they receive ANY signal from their existing AP, regardless of how weak it is.

Say, user boots the mobile device near AP 1, and it connects to AP 1 with a signal strengh of -54 dB / RSSI 34. Now the user walks near AP 2. The device remains connected to AP 1, though signal strengh drops to -85 dB / RSSI 11. Regardless of how long the user stays there, the mobile device never switches to AP 2. Only when he disables and re-enables the WiFi interface on the mobile device, it immediately connects to AP 2 with -52 dB / RSSI 33.

We already changed "Distance between APs" setting from Large to Small, but according to documentation this seems to affect only the connection process, not the roaming threshold.

The supplier of our mobile devices boldly stated that this must be an AP configuration issue and has nothing to do with the mobile devices. Is there anything we overlooked? Any settings that we can modify?

Would we need a Mobility license? From what I read, this seems to support faster roaming (meaning that the outage caused by AP handover is shorter), but it should not be required for roaming itself to work.

Hi,

Roaming is clearly a client side decision !

Witch kind of device is it ?
In computer wifi network card config, you can set the aggressivity level for the roaming behaviour.

The only thing you can do at the controller side is to disallow lower wireless rates in the VSC config ("Allowed wireless rates"). It will strongly force the client to connect on a better signal AP.

Hope it will help you,

Regards,

François

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Roaming is clearly a client side decision !

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This is what I told the mobile device vendor, but he insists that it is a problem in the AP setup. Like the AP should disconnect the device if connection becomes too weak.

Btw, we already disallowed the lowest transfer rates.

The issue affects multiple mobile devices, including Intermec CK3 scanners and Zebra QLn420 printers.

A vendor told you that??? Wow...

A client wants to keep the connection stable. This is why the client will always maintain an existing connection as long as it can. What this means in practice is that the client will never roam when it detects a stronger wireless signal, it will only roam when the quality of the previous connection falls under certain treshold determined by the NIC manufacturer. Some wless clients (for example Intel wless NICs) have a setting in the advanced configuration which allows you to configure the aggressiveness of the roaming.

Disabling lower transfer rates is a device against "sticky client" issue. When you apply that, the AP will disconnect the client when connection is weak... but the final decision to roam is still always made by the client.

Another way to force faster roaming is to reduce the wireless cell size. This you do by reducing the transmit power of the APs. Unfortunately there aren't any hard figures. You can drop the xmit power on APs (testing with one isn't going to help you) to for example 50% and test the behavior, and adjust the value up or down according to the results again testing the effect after every change.. Or you can do a site survey.

Thanks. Well, I assigned that case back to the vendor, but he repeated his statement that it would definitely be the Access Point that has to disconnect the client (which is nonsense obviously).

Reducing signal strengh will not really help, since the client does not roam even with extremely weak signal. We'll play this back to the vendor, asking for a more detailed explanation than just 'the device has the latest firmware so the failure must be on your side'.

Hi All,

Was this problem ever resolved?

I have the same issues currently.

Regards,

Craig.

My experience is that clients do roam when distance is set to small and signal to noise goes below 20db.

Reducing AP power has been the easiest way to obtain that.

On the unified series there is a command: client reject 19 that does it in a more direct way.