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Opportunistic PMK Caching - Complaints |
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Written by Devin Akin
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Monday, 20 August 2007 |
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Having just written a whitepaper on Fast BSS Transition, I decided to look into the nuances of configuring supplicants for Opportunistic PMK Caching (OPC). Holy smokes batman - what a pain it is to find documentation on this. Microsoft says that OPC is supported when you have the KB893357 update loaded: http://support.microsoft.com/kb/893357
Microsoft only gives you the most basic information, like registry entries for PMK caching and preauthentication, but they don't give you anything for OPC. It seems that there is a typo on this page under PMKCacheSize. "Default value: 100" yet the description right below it says the default is 16. I can't find any further documentation.
I decided to see if there were other clients that support OPC. I emailed back and forth with some people at Juniper (proud new owner of Funk Software) about Odyssey Access Client's support of OPC. The resounding answer was, "yes, we support it." I was quite happy to hear this, but after reading through all of their manuals, there's no sign of it in their documentation. I didn't see any manner of OPC, PMK Caching, or even preauthentication configuration. I installed Odyssey Access Client and looked everywhere in the configuration interface, but didn't find anything there either. Supposedly everything is automagic. The problem with that is that you never know when or how it is going to act in a given situation.
With the 802.11r amendment on its way (just under a year away), maybe we'll have something better in the near future. Here's where to keep up with it: http://grouper.ieee.org/groups/802/11/Reports/802.11_Timelines.htm
Cisco has alread publicly stated that they will add 802.11r functionality into their CCX program. The Wi-Fi Alliance has already announced their intention to interoperability test 802.11r functionality starting 1H08 (roughly the same time as the release of the 802.11r amendment, which is currently slated for March 08). That means we have about 9 more months to wait on a standardized, hopefully-configurable, client-side, fast-roaming mechanism.
Oh, and while we're on the topic of fast roaming, to settle the terminology wrangling about what to call Voice over 802.11 - the term "VoWi-Fi" is going to win. I've heard wVoIP (which CWNP and Cisco are using at this point in time), VoFi, VoWiFi, and other variations (with and without hyphens) of the same thing...but you KNOW that the Wi-Fi Alliance's marketing engine is going to make sure we forget all of those other terms quick, fast, and in a hurry. I'm fine with it, but I just wish we could drop the dash and just have VoWiFi. That dash is just weird looking. ;-)
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Recommendation for Wireless Protocol Analyzers....... 
I can understand the desire to control the cache entries, but Microsoft does includes this capability (typos aside).