Now if the client roams over to the new access point, it already has a PMK - the
802.1X authentication phase is skipped.
6.6 Opportunistic PMK Caching: Fast Roaming at Its Fastest
As described in an earlier section, roaming is a key technical advantage of WPA2.
However, even the ???fast roaming??? options included in the standard cause the client a brief
disruption of service, which is too lengthy for some time-sensitive applications.
Currently, establishing a connection to an 802.11 access point, authenticating to it,
and establishing encryption keys can take anywhere from 150 to 350 milliseconds - and in
extreme cases, 800 milliseconds or more. Long delays in establishing connections for
clients occur when, due to the need for access points to communicate with back-end
authentication servers, network equipment is spread out over a wide area.
While PMK Caching and Pre-Authentication within WPA2 help reduce this latency
by reducing redundant instances of 802.1X authentication, experts recognize that this does
not close the ???disruption gap??? that impacts quality of service. Not only does the standard
not address intensive applications, but several implementation and architecture specific
factors can exacerbate the problem in wireless networks.
Pages:
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381