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New Member

802.11n Roaming Card Recommendation

Greetings,

I have tested some of the 802.11n Ubiquiti client cards for roaming and found that the cards will hang on to the AP as long as possible, drop the connection, and then will associate to another AP within range. Another words, there is no configurable exit criteria for these cards. Ubiquiti tech support has confirmed that.

I am looking for some recommendations on good known 802.11n roaming cards that will proactively roam (my setup involves Cisco 1552e APs). The cards need to have drivers for Windows XP.

For example:

1. I have overlapping cells and my client is associated to AP1 at -50dBm.

2. The client moves away from AP1 and is now at -75dBm. The client is now also within range of AP2 with a much better signal. Let's say -45dBm.

3. The client proactively roams to AP2. I don’t expect seamless roaming, but the idea is that the client doesn’t hang on to AP1 until -95dBm.

The signal levels in the above example are just hypothetical. The important part is that when a client hears a signal that's significantly better than the current connection, the client will proactively roam. The difference between the currently connected AP signal and the candidate signal(s) should be spread enough to avoid flapping. It would be even better if this difference (aggressiveness) was tunable.

Option #2

There is a roaming feature on Cisco controllers with lightweight Cisco APs. Here is a summary from WLC Configuration Guide 7.4.

The Cisco UWN solution supports seamless client roaming across lightweight access points managed by the same controller, between controllers in the same mobility group on the same subnet, and across controllers in the same mobility group on different subnets….. You can adjust the default RF settings (RSSI, hysteresis, scan threshold, and transition time) to fine-tune the operation of client roaming using the controller GUI or CLI.”

I understand that to use this feature the clients must support the CCX extensions. Below is one CCXv4 feature that looks promising.

Directed roam request—This feature enables the controller to send directed roam requests to the client in situations when the controller can better service the client on an access point different from the one to which it is associated. In this case, the controller sends the client a list of the best access points that it can join. The client can either honor or ignore the directed roam request. Non-CCX clients and clients running CCXv3 or below must not take any action. No configuration is required for this feature.”

Has anyone tried/tested any of these roaming features with 802.11n CCX client(s)?  Again, my goal is to have the client roam to a significantly better AP once the current AP’s signal is around -75dBm or so.

Thanks in advance!

4 REPLIES
Hall of Fame Super Silver

Re: 802.11n Roaming Card Recommendation

On thing that I use to help with roaming is tweaking the data rates. Some cards are considered "sticky" and will hang on until it drops the connection. Try to disable the lower rates if possible. If you know you don't need 802.11b support, then disable the lower data rates below 12 Mbps for example. If you know what the lowest data rate you can use roaming from each AP, you can set your lowest mandatory to 24 Mbps for example and support the other data rates you want.

Sent from Cisco Technical Support iPhone App

-Scott
*** Please rate helpful posts ***

Re: 802.11n Roaming Card Recommendation

You need a controller based system for your AP.

Hall of Fame Super Gold

Re: 802.11n Roaming Card Recommendation

You need a controller based system for your AP.

Ignore this recommandation.  It's got NOTHING to do with your issue. 

Going back to your issue ... I presume your wireless cards have been updated to the latest drivers?  The "decision" to roam falls entirely on the wireless cards themselves.  The APs have nothing to do with it.  Scott's recommendation, to disable lower data rates, is a very popular (and successful) method in "influencing" the cards to roam.

Depends on how dense is your AP deployment, I always disable anything below 12 Mbps but I have some sites with 18 Mbps disabled too.

New Member

Re: 802.11n Roaming Card Recommendation

The data rate limiting option mentioned by Scott and yourself sounds promising, so thank you both for that. The Ubiquiti cards I am using do have the latest drivers for the WinXP OS that I am supporting, but they are not CCX capable.

Leo's comment may also be worth pursuing and that is what I mentioned in my original post as Option #2. I do have a Cisco controller based deployment, but what I don't know is how the cited roaming features work and was hoping that someone has used/tested these and can recommend a CCX capable NIC, if the roaming reactiveness/aggessiveness results were improved. On paper, the knobs below seem promising, assuming the CCX capable client will honor these.

"You can adjust the default RF settings (RSSI, hysteresis, scan  threshold, and transition time) to fine-tune the operation of client  roaming using the controller GUI or CLI.”

"In the Minimum RSSI text box, enter a value for the minimum received signal strength indicator (RSSI) required for the client to associate to an access point. If the client’s average received signal power dips below this threshold, reliable communication is usually impossible. Therefore, clients must already have found and roamed to another access point with a stronger signal before the minimum RSSI value is reached.

The range is –80 to –90 dBm.

The default is –85 dBm."

"In the Hysteresis text box, enter a value to indicate how much greater the signal strength of a neighboring access point must be in order for the client to roam to it. This parameter is intended to reduce the amount of roaming between access points if the client is physically located on or near the border between two access points.

The range is 3 to 20 dB."

"In the Scan Threshold text box, enter the minimum RSSI that is allowed before the client should roam to a better access point. When the RSSI drops below the specified value, the client must be able to roam to a better access point within the specified transition time. This parameter also provides a power-save method to minimize the time that the client spends in active or passive scanning. For example, the client can scan slowly when the RSSI is above the threshold and scan more rapidly when the RSSI is below the threshold.

The range is –70 to –77 dBm.

The default is –72 dBm."

I also wonder if the AP can influence roaming by sending a deauth to the STA. Then the STA would associate to a closer/better signal AP ...

Regards

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