Friday, December 7, 2012

Wi-Fi Fast Roaming is Here! (Finally)

It's been a long time coming, but industry support for standards-based fast roaming is finally starting to emerge! See my previous posts:

http://revolutionwifi.blogspot.com/2010/06/its-time-for-80211r.html

http://revolutionwifi.blogspot.com/2012/02/wi-fi-roaming-analysis-part-2-roaming.html

Apple iOS now officially supports IEEE 802.11r and 802.11k, which form the underpinnings of the Wi-Fi Alliance Voice Enterprise certification for fast roaming. (Don't be confused by the word voice in the certification. This is applicable to any WiFi client that needs fast roaming capability at the driver level for any application.)

This will help Apple mobile devices perform better in enterprise environments, especially when multimedia and collaboration tools are used with BYOD.

From Apple's website:
http://support.apple.com/kb/HT5535

"iOS 6 introduces support for optimized client roaming on enterprise Wi-Fi networks. The 802.11 Working Group standards k and r were conceived to give wireless clients the ability to more seamlessly roam from access point (AP) to access point within the same network.

802.11k
802.11k allows an iOS 6 device to quickly identify nearby APs that are available for roaming. When the signal strength of the current AP weakens and the iOS device needs to roam to a new AP, it will already know the best candidate AP with which to connect.

802.11r
When an iOS 6 device roams from one AP to another on the same network, 802.11r streamlines the authentication process using a feature called Fast Basic Service Set Transition (FT). FT allows iOS 6 devices to associate with APs more quickly. Depending on your Wi-Fi hardware vendor, FT can work with both preshared key (PSK) and 802.1X authentication methods.

Coupled with 802.11k's ability to quickly identify the target AP, FT's faster association method may enhance application performance and aims to provide a better Wi-Fi experience in iOS.

Additional Information
Not every Wi-Fi network hardware vendor currently supports 802.11k and 802.11r. Check with the manufacturer of your Wi-Fi hardware (controllers and APs) to determine if support is available. Once support for both standards is verified, 802.11k and FT functionality must be enabled. Setup methods vary; please consult the current configuration documentation for your Wi-Fi hardware for details."

Cheers,
Andrew

9 comments:

  1. Good post, but I have a question about 802.11k. As far as I understand 802.11k allows the APs to guide the client to nearby candidate APs. From the client's perspective, why wouldn't it just do a background scan to see who is nearby?

    Is the purpose of 802.11k to minimize probe requests/responses to gather this information when the AP/controller can provide a more intelligent sublist? What information is provided by 802.11k? Just BSSIDs of candidates or do they also provide the current RSSIs from your client's perspective? Given the list of candidates, how would my client pick the optimal AP?

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    1. Hi Scott,
      Clients must go off-channel to perform background scanning. This takes time and degrades client performance, so they only do this periodically or when their SNR drops below a threshold triggering an immediate scan. The 802.11k neighbor information allows the AP to which the client is connected to provide a list of neighbor APs that can handle the connection should the client wish to roam. This allows the client to maintain a list of potential APs to roam to, their channels, and load without having to go off-channel. This is of particular benefit with 5GHz since there are so many 20 MHz channels available. It would take a while to scan all of them by a client.

      Cheers,
      Andrew

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  2. Does Cisco call 802.11k something else in their WLC? I don't find any mention of it in the release notes.

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    1. You can find mention of partial 802.11k support in the 7.4 Release Notes for the 5508 WLC here:
      http://www.cisco.com/en/US/docs/wireless/controller/release/notes/crn74.html

      Cheers,
      Andrew

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  3. I'm learning much on this blog. Thanks! Do you know of client devices that support 802.11r. I'm actually looking for a rugged 802.11n client workgroup bridge that could run in vehicles on Cisco unified outdoor mesh infrastructure.

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    1. Apple iOS devices support 11r on code version 6.0 and later. Also several Broadcom and QualcommAtheros chipsets support it, so you could cross-reference the Wi-Fi Alliance Voice-Enterprise certified chipsets with a specific device you may be looking at to find out. I think there is one Blackberry certified too.

      As for an 11n WGB, you should use an AP from the same manufacturer in Mesh or WGB mode.

      Andrew

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  4. Hi Andrew, thanks for your information here. I am too looking for specific mobile chipsets supporting this Wi-Fi 802.11r. I got to know from that MTK chipsets do not support. As per you there are few Broadcom and Qualcomm chipsets support, but not getting direct information on which all chipsets (chipset numbers) support these. Also would like to understand if this 802.11r support has to be in base mobile chipset or it has to be additional wi-fi only chipset?

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    Replies
    1. Go to the Wi-Fi Alliance website and lookup devices that are Voice-Enterprise certified.

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