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Wireless Features

How To Tell - 802.11v

802.11v is the IEEE standard focused on the process of STAs making a BSS transition. Key features of the spec are summarized in the 7signal slide below.

802.11v BSS Transition Management

802.11v BSS Transition Management

For 11v, we look for BSS Transition: Supported (wlan.extcap.b19 == 1). If it's supported, you'll find it in AP Beacons and Probe Responses, which are plentiful, but only in STA association or reassociation frames, which are not. So if you're looking for STAs that support 11v BSS Transition, you should add filters for Association (wlan.fc.type_subtype == 0) and Reassociation (wlan.fc.type_subtype == 2) requests to the filter, as shown below.

11v BSS Transition supported

11v BSS Transition supported

You can also AND the BSS Transition filter with your STA's MAC address to home right in.

Using STA MAC address to find 11v support

Using STA MAC address to find 11v support

Once we know 11v is supported, we can filter for BSS Transition Management Requests (wlan.fixed.action_code == 7) and Responses (wlan.fixed.action_code == 8). Here's Orbi issuing the request, and supplying a Neighbor Report to try to aid the move. I'm not sure if it is part of the standard, but the Candidate list obfuscates the suggested BSS, which I've circled in red.

11v BSS Transition Management Request

11v BSS Transition Management Request

The Intel STA's response clearly indicates the target BSS, however.

11v BSS Transition Management Request

11v BSS Transition Management Request

The 7signal slide shows three other ways APs or STAs can make roam requests or suggestions. But I haven't been able to track down the filters to check for them.

How To Tell - 802.11r

The last of the three roaming assistance standards is 802.11r Fast Roaming/Fast BSS Transition. This appears to be the least implemented (or enabled) of the three, because it can cause problems for older devices, which may be unable to connect to an AP because they can't understand the additional 11r information in AP beacons and probe responses.

The 7signal summary slide shows 11r's focus is reducing authentication time. 11r is focused on enabling sub-second roaming, which is most important for uninterrupted voice or video calling.

802.11r BSS Fast Transition

802.11r BSS Fast Transition

AP 11r support indication is found in the RSN-IE (Robust Security Network Information Element), Authentication Key Mangement (AKM) Suite. If you apply a wlan.rsn.akms.type == 4 filter and see type = FT using PSK, you found it ! Applying this filter, however, returns no hits on captures of either the Samsung Tab or Intel AC 8260. So I have to say neither supports 11r.

The screenshot below shows what it looks like in a capture I ran across in an online archive.

11r support indicator

11r support indicator

Filtering for wlan.tag.number == 55 will show Authentication or Reassociation frames with the Fast BSS Transition.

11r support indicator

11r support indicator

I've seen 11r support only once in my captures, on a Ubiquiti UAP-AC-Lite.

Update 8/16/18 - I've learned that STAs will not advertise 11r support unless they detect an AP advertising 11r support. Since the Orbi doesn't support 11r, I had no way of properly detecting STA 11r support.

Closing Thoughts

I know this information might be arcane or uninteresting to some. But I hope it saves someone the hours it took me to track all this down. Like many new Wi-Fi technologies that are supposed to enhance our experience, 802.11k,v and r are taking a long time to make their way into widespread implementation. And it's not like they're new; 11k and 11r were released in 2008 and 11v in 2010.

Also typically for Wi-Fi, implementations vary widely. These standards leave lots of room for interpretation, with many optional features. So to repeat an answer I gave to an SNBForums member, not all 11k, v or r implementations are created equal. Just because your Wi-Fi system and devices say they support one or more of these roaming assistance technologies, doesn't mean that quick and smooth roaming is assured. And it's possible that your roaming experience can be just fine without them.

In the end, the two most important factors in smooth roaming are client behavior and AP overlap--on both bands! 802.11k and v, and to a lesser extent, r support are still a work very much in progress.

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