STA disassociation behavior

1
STA disassociation behavior

• Joe Kwak, Marian Rudolf
• InterDigital

2
Disassociation behavior as mandated in current
specification

• 5.4.2.4 Disassociation
• The disassociation service is invoked whenever an
  existing association is to be terminated.
  Disassociation is a DSS.
• In an ESS, this tells the DS to void existing
  association information. Attempts to send
  messages via the DS to a disassociated STA will
  be unsuccessful.
• The disassociation service may be invoked by
  either party to an association (non-AP STA or
  AP). Disassociation is a notification, not a
  request. Disassociation cannot be refused by
  either party to the association.
• APs may need to disassociate STAs to enable the
  AP to be removed from a network for service or
  for other reasons.
• STAs shall attempt to disassociate whenever they
  leave a network. However, the MAC protocol does
  not depend on STAs invoking the disassociation
  service. (MAC management is designed to
  accommodate loss of an associated STA.)

3
Disassociation behavior in practice

• refering to last paragraph (highlight in red)
• STA may or may not send a DISASSOCIATION frame
  to the AP when leaving a network, for example at
  power-down
• Current STA implementations w.r.t disassociation
  behavior in normal, non-pathologic situations
  vary widely, some try, most do not even try

4
Why is this a problem ?

• Currently, most STAs passively disappear and AP
  experiences large uncertainty w.r.t. STAs still
  camping in the BSS
• The knowledge of how many STAs are currently
  associated / authenticated, i.e. in the system
  is key to any form of load and admission control
  in the .11 network
• Use of activity-based time-out counters not good
  enough for RRM and network management purposes,
  it is also a security threat
• But in 11k, we can provide this kind of
  indication to the AP, an extremely valuable
  information to the network

5
Proposal

• We suggest to make sending the DISASSOCIATION
  frame mandatory when STAs leave a network in the
  sense of the current paragraph 5.4.2.4
• The idea is to capture the 99 of STAs leaving
  a BSS in controlled manner (power down or
  switching off etc.), but not to account for all
  thinkable pathologic cases (STA falling into the
  bath-tube or PCMCIA card extracted, etc)
• Our proposal for the way to capture this behavior
  in the specs write this into the PICS, and
  strengthen the requirement wording.

6
Strengthen Disassociation Behavior Wording

• 5.4.2.4 Disassociation
• The disassociation service is invoked whenever an
  existing association is to be terminated.
  Disassociation is a DSS.
• In an ESS, this tells the DS to void existing
  association information. Attempts to send
  messages via the DS to a disassociated STA will
  be unsuccessful.
• The disassociation service may be invoked by
  either party to an association (non-AP STA or
  AP). Disassociation is a notification, not a
  request. Disassociation cannot be refused by
  either party to the association.
• APs may need to disassociate STAs to enable the
  AP to be removed from a network for service or
  for other reasons.
• STAs shall attempt to disassociate whenever they
  leave a network, power down or become incapable
  of continuing network service. However, the MAC
  protocol does not depend on STAs invoking the
  disassociation service. (MAC management is
  designed to accommodate loss of an associated
  STA.)

7
Proposed PICS Element
8
Motion for Disassociate normative text

• Move to instruct the editor to incorporate text
  from document 11-04-0105-00-000k-Shall_Disassociat
  e.doc into next TGk draft specification document
• Moved by Joe Kwak
• Seconded by _______________
• Vote YEA _______
• Vote NEA _______
• ABSTAIN _______
• Vote Passes/Fails at ___