Relationships Between Services

An STA keeps two state variables for each STA with which direct communication via the WM is needed:

  • Authentication state  The values are unauthenticated and authenticated.

  • Association state  The values are unassociated and associated.

These two variables create three local states for each remote STA:

  • State 1  Initial start state, unauthenticated, and unassociated

  • State 2  Authenticated, not associated

  • State 3  Authenticated and associated

The current state existing between the source and destination station determines the IEEE 802.11 frame types that may be exchanged between that pair of STAs. The allowed frame types are grouped into classes and the classes correspond to the station state. In State 1, only Class 1 frames are allowed. In State 2, either Class 1 or Class 2 frames are allowed. In State 3, all frames are allowed (Classes 1, 2, and 3). The frame classes are defined as follows:

  1. Class 1 frames (permitted from within States 1, 2, and 3)

    1. Control frames

      1. Request to Send (RTS)

      2. Clear to Send (CTS)

      3. Acknowledgment (ACK)

      4. Contention-free end (CF-End)+ACK

      5. CF-End

    2. Management frames

      1. Probe request/response.

      2. Beacon.

      3. Authentication: Successful authentication enables a station to exchange Class 2 frames. Unsuccessful authentication leaves the STA in State 1.

      4. Deauthentication: Deauthentication notification when in State 2 or State 3 changes the STA’s state to State 1. The STA will become authenticated again prior to sending Class 2 frames.

      5. Announcement traffic indication message (ATIM).

    3. Data frames

      1. Data: Data frames with frame control (FC) bits To DS and From DS are both false.

  2. Class 2 frames (if and only if authenticated; allowed from within States 2 and 3 only)

    1. Management frames

      1. Association request/response

        • Successful association enables Class 3 frames.

        • Unsuccessful association leaves STA in State 2.

      2. Reassociation request/response

        • Successful reassociation enables Class 3 frames.

        • Unsuccessful reassociation leaves the STA in State 2 (with respect to the STA that was sent the reassociation message). Reassociation frames will only be sent if the sending STA is already associated in the same ESS.

      3. Disassociation

        • Disassociation notification when in State 3 changes a station’s state to State 2. This station will become associated again if it wishes to utilize the DS. If STA A receives a Class 2 frame with a unicast address in the Address 1 field from STA B that is not authenticated with STA A, STA A will send a deauthentication frame to STA B.

  3. Class 3 frames (if and only if associated; allowed only from within State 3)

    1. Data frames

      1. Data subtypes: Data frames allowed. That is, either the To DS or From DS FC bits may be set to true to utilize DSSs.

    2. Management frames

      1. Deauthentication: Deauthentication notification when in State 3 implies disassociation as well, changing the STA’s state from 3 to 1. The station will become authenticated again prior to another association.

    3. Control frames

      1. Power-save poll (PS-Poll)

If STA A receives a Class 3 frame with a unicast address in the Address 1 field from STA B that is authenticated but not associated with STA A, STA A will send a disassociation frame to STA B. If STA A receives a Class 3 frame with a unicast address in the Address 1 field from STA B that is not authenticated with STA A, STA A will send a deauthentication frame to STA B.



Hotspot Networks(c) Wi-Fi for Public Access Locations
Hotspot Networks(c) Wi-Fi for Public Access Locations
ISBN: N/A
EAN: N/A
Year: 2005
Pages: 88

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net