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Probe Request and Response in TGai

Probe Request and Response in TGai. Authors:. Date: 2011-1 1-02. Abstract. This document describes a technical proposal for TGai which addresses the following phase. AP Discovery. Conformance w/ TGai PAR & 5C. Background.

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Probe Request and Response in TGai

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  1. Katsuo Yunoki, KDDI R&D Laboratories Probe Request and Response in TGai Authors: • Date: 2011-11-02

  2. Katsuo Yunoki, KDDI R&D Laboratories Abstract • This document describes a technical proposal for TGai which addresses the following phase. • AP Discovery

  3. Katsuo Yunoki, KDDI R&D Laboratories Conformance w/ TGai PAR & 5C

  4. Katsuo Yunoki, KDDI R&D Laboratories Background • Time occupied situation in the real case was presented in Doc. 11-11/1413r0. • The time occupied rate will become higher and higher because of Smartphone increasing. • Thus, we have to consider reducing needless packet exchanges which occur packet collisions and bigger latency in order to obtain the FILS advantages effectively.

  5. Katsuo Yunoki, KDDI R&D Laboratories Probe Request/ Response • In order to search the surrounding APs, a STA receives Beacon and transmit Probe Request in Broadcast. • APs transmit Probe Response for responding received Probe Requests in unicast. STA AP1 AP2 AP3 AP4 Probe Request (wildcard) Probe Response

  6. Katsuo Yunoki, KDDI R&D Laboratories Example of Probe Request • This STA transmits multiple “Probe Request” about every 15 seconds. • 5 Probe Requests were observed around time stamp of 104 seconds. * Source MAC address was modified.

  7. Katsuo Yunoki, KDDI R&D Laboratories Example of Probe Response • 3 SSID were responded for probe requests. • 26 probe responses were observed for 5 probe requests in Slide 7.

  8. Katsuo Yunoki, KDDI R&D Laboratories Considerations • “Probe Request / Response” cause packet flooding even if the STA doesn’t have any connecting capabilities to surrounding APs. • Transmitting “Probe Request” every 15 seconds doesn’t help the fast AP discovery. • As mentioned in Doc. 11-11/1413r1, probe responses existed 5 times more than probe requests at that monitored public space. • Avoiding needless packets may bring clearer WLAN air circumstances.

  9. Katsuo Yunoki, KDDI R&D Laboratories Probe exchangesAssumption-1 If 5 APs are installed in public space, 5 probe responses will be transmitted for a probe request with wildcard SSID. STA AP1 AP2 AP3 AP4 AP5 Probe Req. (wildcard SSID) Probe Res. (unicast)

  10. Katsuo Yunoki, KDDI R&D Laboratories Probe exchangesAssumption-2 If 5 STAs enter into the same place, 25 probe responses will be transmitted. STA1 STA2 STA3 STA4 STA5 AP1 AP2 AP3 AP4 AP5

  11. Katsuo Yunoki, KDDI R&D Laboratories Probe exchangesAssumption-3 What happens when a crowded train enter into the same place? AP1 AP2 AP3 AP4 AP5 How many probes will be exchanged??? STA STA STA STA STA STA STA STA STA STA STA STA STA STA STA STA STA STA

  12. Katsuo Yunoki, KDDI R&D Laboratories Why not use Beacons for AP discovery? • Beacon is including the almost same IEs as Probe Response. • Beacon is transmitted in every 100 milliseconds. • A STA can receive 150 Beacons during transmitting 1 Probe Request, if it would transmit Probe Request in every 15 seconds. It would be sufficient for a STA to discover AP with the target SSID by Beacons. • Mobile devices (Smart-phones) are battery consumption critical. So it is preferable for mobile devices not to transmit “Probe Requests”, if possible.

  13. Katsuo Yunoki, KDDI R&D Laboratories Open discussion • Is Probe Request with wildcard SSID necessary for AP discovery? Why so? • I’m thinking that even Probe Request with a specific target SSID isn’t necessary for AP discovery of public Wi-Fi hotspots. • Stealth APs should be discovered by Probe Request/Response exchanges. But it isn’t by Probe Request with wildcard SSID.

  14. Katsuo Yunoki, KDDI R&D Laboratories Proposal • I’d like to propose that: • TGai compliant STAs shall not use the wildcard SSID in SSID element of “Probe Request”. • TGai compliant APs shall not transmit “Probe Response” for “Probe Request” with the wildcard SSID. • More TGai compliant devices would be deployed, clearer WLAN circumstances might be realized!!

  15. Katsuo Yunoki, KDDI R&D Laboratories References • doc.: IEEE 11-11/1413r0

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