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Difference between WLAN class1 class2 and class3

This page describes difference between WLAN class1, class2 and class3 as per IEEE 802.11 WLAN standard.

Figure-1 below depicts 802.11 state diagram. As shown allowed frame types vary with the association and authentication states. Stations are either authenticated or unauthenticated and can be associated or unassociated. These two variables can be combined into three allowed states.

802.11 state diagram

There are three states as mentioned below:

State-1. Initial state; not authenticated and not associated
State-2. Authenticated but not yet associated
State-3. Authenticated and associated

WLAN Class1 frames

a) WLAN Class 1 frames (permitted from within States 1, 2, and 3)
1) Control frames
i) Request to send (RTS)
ii) Clear to send (CTS)
iii) Acknowledgment (ACK)
iv) Contention-Free (CF)-End+ACK
v) CF-End
2) Management frames
i) Probe request/response
ii) Beacon
iii) Authentication: Successful authentication enables a STA to exchange Class 2 frames.
Unsuccessful authentication leaves the STA in State 1.
iv) Deauthentication: Deauthentication notification when in State 2 or State 3 changes the
STA's state to State 1. The STA shall become authenticated again prior to sending Class 2
frames. Deauthentication notification when in State 3 implies disassociation as well.
v) Announcement traffic indication message (ATIM)
vi) Spectrum Management Action: Within an IBSS, action frames are Class 1.
3) Data frames
i) Data: Data frames between STAs in an IBSS with frame control (FC) bits "To DS" and "From DS" both false.

Control Management Data
RTS Probe Request Any frame with ToDS and FromDS false(0)
CTS Probe Response
Acknowledgment Beacon
CF-End Authentication
CF-End+CF-Ack Deauthentication
ATIM(Announcement Traffic Indication Message)

WLAN Class2 frames

WLAN Class 2 frames (if and only if authenticated; allowed from within States 2 and 3 only)
1) Management frames
i) Association request/response: Successful association enables Class 3 frames.
Unsuccessful association leaves STA in State 2.
ii) 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 shall only be sent if the sending
STA is already associated in the same ESS.
iii) Disassociation: Disassociation notification when in State 3 changes a STA's state to
State 2. This STA shall 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 shall disallow the received Class 2 frame and send a
deauthentication frame to STA B.

Control Management Data
None Association Request/Response None
Reassociation Request/Response

WLAN Class3 frames

WLAN Class 3 frames (if and only if associated; allowed only from within State 3)
1) Data frames
i) Data subtypes: Data frames allowed, i.e., either the "To DS" or
"From DS" FC bits may
be set to true to utilize the DSS.
ii) QoS data subtypes allowed to/from non-AP STA(s) that are associated with AP(s).
iii) Data frames between STAs in a BSS with FC bits "To DS" and
"From DS" both false.
2) Management frames
i) QoS, DLS, and Block Ack Action
3) Control frames
i) Power save (PS)-Poll
ii) Action: Within an infrastucture BSS, action frames are Class 3.
iii) Block Ack (BlockAck)
iv) Block Ack Request (BlockAckReq)

Control Management Data
PS-Poll Deauthentication any frames including those with either the ToDS or FromDS bits set

WLAN MAC frames Links

WLAN Association Request and response frame
WLAN authentication Request and deauthentication frame
WLAN beacon frame
WLAN passive vs active scanning frame
WLAN Probe Request and response frame
WLAN reassociation Request and response frame
WLAN RTS and CTS frame

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