Use of FILS Discovery Frame as optional Probe Response

1. Use of FILS Discovery Frame as optional Probe Response Authors: Date: 2012-07-18 Graham Smith, DSP Group

2. Abstract The FILS Discovery frame has been proposed as a minimal indication for STAs carrying out passive scanning on information on the AP. The suggestion is that this frame could also be used as a minimal Probe Response if the AP so chooses. The intention is to mitigate Probe Request/Response storms. Graham Smith, DSP Group

3. Background • The Probe Response is of a significant size and under certain conditions, it is desirable to reduce its size as much as possible. • If AP detects that a Probe Request storm is present or likely to happen, then individual responses to each request become undesirable. However, the AP does want STAs to associate with it • If there is a potential Probe Request/Response storm, then the desirable action is that STAs move to the Passive Scanning mode. • At present there is nothing of substance that addresses mitigating a Probe Request/Response storm and this scheme enables a smooth changeover between active and passive scanning Graham Smith, DSP Group

4. Overview of Usage • An AP determines that active scanning has the potential to cause blocking • When this situation is identified, the AP starts by responding with the FILS Discovery frame – broadcast. • Other FILS STAs, as well as the originating FIL STA, will see the FILS Discovery frame and realize what is going on, i.e. they soon realize that no reason to send a probe request if a FILS Discovery frame is responding. Graham Smith, DSP Group

5. Possible consequences • If AP starts sending FILS Discovery frame in response to the probe, then possible outcomes are: • FILS AP decides to periodically send the FILS Discovery frame • FILS STAs could automatically switch to passive scanning or still send probes to force the immediate response rather than wait for Beacon • Legacy STAs do not understand the response and may or may not send probe again or simply move on. (see later) • Converse would also occur if ‘traffic’ dies down: • AP could start to respond to probe(s) with Probe Response Graham Smith, DSP Group

6. Discussion Points • Legacy STAs have no expectation of fast link set up • FILS STAs do have expectation of fast link setup • Omission of Probe Response is already in SFD (6.1.6) hence many arguments put forward against using the FILS Discovery frame (in discussions on r0) are moot in view of this: • If no response, same as FILS DF being missed • Sending the FILS DF is one better than sending nothing • This is a potentially elegant scheme to bridge the active to passive gap: • Analysis has shown passive scanning is required at a certain level of STAs wishing to associate. Need to encourage move over from active to passive. • By using the FILS DF as a common factor, this does provide a method. Graham Smith, DSP Group

7. Motion 1 • Add to the Specification Framework Document the following to a new subheading “General 5.1”: • “P802.11ai shall include method(s) for mitigating Probe Request/Response storms” • Moved: • Seconded: Graham Smith, DSP Group

8. Motion 2 • Add to the Specification Framework Document the following to a new subheading “General 5.1”: • “P802.11ai shall include method(s) to enable a FILS network to encourage non-AP STAs to use passive rather than active scanning at a point where the use of active scanning causes the network to be in danger of being blocked or the available bandwidth to be significantly restricted.” • Moved: • Seconded: Graham Smith, DSP Group

9. Motion 3 • Add to the Specification Framework Document the following to a new subheading “General 5.1”: • Assuming that Motion 2 has been accepted, the following text shall then be added: • “A FILS AP choosing to cease sending unicast Probe responses and to transit FILS Discovery frames as a method to encourage non-AP STAs to use passive rather than active scanning, should be considered. ” • Move: Graham • Seconded: Yes: • No; • Abst: Graham Smith, DSP Group