Cutting Though Traffic Like a Flying V

The 802.11v amendment has been voted, stamped and added.  It is part of the 802.11 standard.  We still are unsure if we'll ever see it, but if we do it could ease some concerns about high-density WiFi.

Wireless Network Management is its name, and not being adopted is 802.11v's game.

Wireless network management (WNM) is an addition to the 802.11 standard that puts more control in the hands of admins.  Today, the client/station controls everything: roaming, load balancing and congestion avoidance included.  WNM is designed to put that stuff in the hands of the infrastructure (APs, controllers and management software).

Companies that sell client/stations have (predictably?) declined to adopt WNM thus far.  That means that admins will continue to have to wait for the ultimate careful-what-you-wish for WiFi technology.

There is, however, one part of WNM that is separate from the move to infrastructure control: Multiple BSSID Beacons.  APs have supported multiple BSSIDs for a long time (and Beacons for even longer), but until 802.11v/WNM, the two were never put together.

Multiple BSSID Beacons are important because they could cause a reduction in channel overhead.  Many WiFi networks that support an array of users are hamstrung by the fact that each BSSID takes up about 2.5% of available 2.4 GHz channel time.  (I wish I could take credit for that calculation, but it was an engineer from Ascom who did the math and relayed it to me.)  That means that a hockey arena deployment that supports separate SSIDs for Team, media, concessions, ticket scanning, audio/visual and guests would lose 15% (6 x 2.5%) of available channel time from each AP.  If the big open spaces like the arena bowl have areas where APs on channels 1, 3, 5 and 7 (a bad channel design, but it happens) are covering the same space, then each of those APs would be losing somewhere between 45% and 60% of available channel time before the first data frame is sent.  If all six of those SSIDs could be contained in one Beacon, the Beacon overhead could be reduced to 10% or less on each channel.

Who knows if 802.11v/WNM Multiple BSSID Beacons will ever be adopted.  Hockey fans already saw the Flying V cut through the neutral zone trap to perfection, only to have it go unadopted by those stodgy NHL coaches.  Let's hope that WiFi vendors treat our V differently.


  1. I love those statistics, have you got any maths or paperwork supporting them, or was this an ad-hoc email conversation between you and your Ascom contact?

  2. Hi Ben,
    Good topic! It would definitely be nice to see WNM services implemented to improve performance and efficiency of Wi-Fi networks. We are starting to see two related topics being adopted in products, namely fast secure roaming (802.11r) and radio resource measurement (802.11k), and I think WNM (802.11v) is next on the docket. 802.11r and 802.11k could be argued to lay the groundwork for a bit more sophistication with 802.11v in my opinion. Whereas 802.11k is concerned with the radio environment, 802.11v expands it to include broader operational data surrounding existing network conditions allowing stations to be more cognizant of the topology and state of the network.

    However, it's important to be clear that 802.11v does NOT give control to infrastructure APs or Controllers. 11v allows APs and stations to exchange information so that both are more aware of network conditions and so that clients "more informed" in their own decision making. But it doesn't move control to the infrastructure! Semantics are important here in my opinion.

    As for the Multiple BSSID capability, this has been implemented before using the SSID List (SSIDL) which was developed between Cisco and Microsoft using the WPS Information Element. Not standards-based, but it should be noted as a precursor. As with most features, now that the standards-based version is out I think we'll see more broader adoption instead of the very limited fragmented support we see prior (this is true with fast secure roaming in my opinion too). Here is a link on that SSIDL for your reference:

    Another cool 802.11v WNM service in my opinion is the BSS Transition Management capability. It is of interest regarding fast roaming, whereby an AP can request a client to roam to another AP for better performance or capacity reasons. I think this service will be one of the first WNM services we will see implemented in both infrastructure and clients. I hear rumblings of this being developed already by a few WLAN vendors :)

    Andrew von Nagy

  3. MaccA: I was shown the math on Beacon overhead. Paperwork on that stuff costs lots and lots of money. Though that fails to stop people from asking me for it for free all the time.

    AvN: I get what you're saying, but the BSS TM is precisely what I'm talking about when I say that infrastructure is given more control.

  4. @ Ben: This is an interesting Topic to debate on, influence of Number of BSSID's on Channel Airtime. You may look at this Blog on the Math discussed by Nigel and the other Factors which influence Channel AirTime.

    If we go with Multiple BSSID's in the same Beacon then we are adding a lot of overhead to the Beacon Size and with the Number of Vendor specific IE's in a Beacon this will increase the Air Time used by Beacons.

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