Thursday, March 1, 2018

Chapter 2 - 802.11 State Machine

"State Machine" would be a great name for a punk band don’t you think?
There are three states that clients can be in according to the 802.11 standard

  • Unauthenticated/Unassociated
  • Authenticated/Unassociated
  • Authenticated/Associated

The first state, Unauthenticated/Unassociated basically means that the STA is not connected to the WLAN. Any frames sent are not passed on through the AP.

The second state, Authenticated/Unassociated is a rarely seen one. Essentially the client device has already given the doorman the secret handshake and shown him their membership ring and at this point is allowed into the foyer. Normally they are passed quickly through to the next state. However there are times when the AP may be at capacity or some other issue may arise where although they are Authenticated, they are not allowed entrance. At this point they are normally kicked back out to the Unauthenticated state.

The third state Authenticated/Associated means the client has made it past the foyer and has made their way into the wondrous world of the LAN.

Association Response Frame - When the AP sends the association response frame to the client it includes a status code. This is kind of like a college acceptance letter. You know you are going to get a letter of some kind back from the college, but you aren't sure what will be inside. If the status code is a 0 then you're association request was successful, or to further metaphor you were accepted to the college! Congratulations! There are a couple other status codes that indicate that you unfortunately didn’t make the cut for a number of reasons. If it’s a 12, then its something outside the standard. Maybe the admissions persons dog ate your application or something. If it’s a 17, that means that the AP is full and is serving the maximum number of STA's. Basically the college would love to accept you, but the fire warden says that they are full. If its an 18 though… an 18 means that the STA does not support all of the basic rates that the BSS requires. To continue with our metaphor, your SAT scores were too low.

***EXAM*** The above will more than likely be on the exam, so I'm just going to put it quickly here without the metaphor

Status Code 0 - Association request succesful
Status Code 12 - Association rejected due to something outside the standard
Status Code 17 - Association rejected because the AP is full
Status Code 18 - Association rejected because the STA doesn’t support all the minimum requirements

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