Fujio Watanabe, Moo Ryong Jeong, Toshiro Kawahara Month 2002 doc.: IEEE 802.11-02/xxxr0 November 2004 AP Scanning Fujio Watanabe, Moo Ryong Jeong, Toshiro Kawahara DoCoMo USA Labs fwatanabe@ieee.org Fujio Watanabe, DoCoMo USA Labs John Doe, His Company

Background Channel scanning is a time-consuming process November 2004 Background Channel scanning is a time-consuming process Passive scan: several beacon intervals per channel (e.g., >100ms) Active scan: 15 msec per channel Channel scanning scheme is within/without scope of TGr? VoIP scenario Measurement Results SSID Overlap Related Documents Fast Active Scan for Measurement and Handoff (03/416r0) Fast Active Scan Proposal (03/623r0, 03/623r2) Fujio Watanabe, DoCoMo USA Labs

VoIP Scenario (FOMA/WLAN) November 2004 VoIP Scenario (FOMA/WLAN) Presence Server Intra Server Business Application Server AS SIP Server PSTN Router AP AP Fixed Phone Fast Roaming Reference: http://www.nttdocomo.co.jp/new/contents/04/whatnew0713-1.html Fujio Watanabe, DoCoMo USA Labs

Channel Scanning Time Scanning time represents Month 2002 doc.: IEEE 802.11-02/xxxr0 November 2004 Channel Scanning Time Scanning time represents majority of Transition Process Time Reference : Slide 13. [3] J. Spilman et al, “Test Methodology for Measuring BSS Transition Time,” IEEE 802.11-04/0748r1 Fujio Watanabe, DoCoMo USA Labs John Doe, His Company

SSID Overlap SSID can be set to any value SSID: November 2004 SSID Overlap SSID can be set to any value Non-Intentional duplication Identical name can be used accidentally by multiple parties (e.g., same office people) Intentional duplication Malicious AP copies SSID as well as BSSID SSID: Can be used to distinguish between networks Does not insure accessibility to network Fujio Watanabe, DoCoMo USA Labs

November 2004 Problems Time consuming scanning results in large measurement overhead and potential handoff interruption. Miss-selection of AP (same SSID) causes potential handoff interruption. Critical for Voice Applications Fujio Watanabe, DoCoMo USA Labs

Current Active Scanning Procedure Month 2002 doc.: IEEE 802.11-02/xxxr0 November 2004 Current Active Scanning Procedure Use of DCF in probe response transmission is source of time-consumption DCF is used in current standard on assumption that STA has no knowledge about neighbor APs STA wants to obtain information on all neighbor APs Probe request is broadcast so that any AP (SSID overlap) can hear and respond by sending probe response Fujio Watanabe, DoCoMo USA Labs John Doe, His Company

Unicast Probe Request Prior knowledge on neighbor APs assumed Month 2002 doc.: IEEE 802.11-02/xxxr0 November 2004 Unicast Probe Request Prior knowledge on neighbor APs assumed Probe request is sent as a directed frame to a specific AP on the AP’s operation channel with BSSID in DA field and BSSID field AP responds to the directed probe request after SIFS Response shall be an ACK frame AP sends the probe response later Probe response may be omitted if requested in the probe request STA can learn availability/unavailability of the desired AP after SIFS When STA receives ACK, the desired AP is available If probe response is not requested, STA may leave the channel since the scanning for the AP is done If probe response is requested, STA stay on the channel unlit it receives the probe response from the AP When STA does not receive ACK, the desired AP is not available Or PIFS Fujio Watanabe, DoCoMo USA Labs John Doe, His Company

Advantages Short Scanning Time November 2004 Advantages Short Scanning Time Filter out APs with the same SSID (non-intentional) Fujio Watanabe, DoCoMo USA Labs

Alternative Scheme 1 AP sends ACK after SIFS period November 2004 Alternative Scheme 1 AP sends ACK after SIFS period When probe response is ready, send it with DIFS deferral (and random backoff) Probe response is retransmitted unless ACK is received MaxChannelTime MinChannelTime Scanning Station Probe to APi Ack APi Ack Other frames P Response SIFS SIFS DIFS Random Backoff Fujio Watanabe, DoCoMo USA Labs

Alternative Scheme 2 AP sends ACK after SIFS period Ack Scanning November 2004 Alternative Scheme 2 AP sends ACK after SIFS period MinChannelTime Scanning Station Probe to APi APi Ack SIFS Fujio Watanabe, DoCoMo USA Labs

November 2004 Proposed changes Allow STA to send directed probe request (unicast probe request frame) AP shall reply with ACK and may send the probe response later Fujio Watanabe, DoCoMo USA Labs

Month 2002 doc.: IEEE 802.11-02/xxxr0 November 2004 Conclusion We considered improvement of active scanning for real time application (e.g., VoIP) Our schemes accelerate active scanning process when there is prior knowledge on neighbor APs information (defined TGk) Proposed active scanning schemes are effective for: Reducing handoff time Filter out APs with the same SSID (non-intentional) Fujio Watanabe, DoCoMo USA Labs John Doe, His Company

November 2004 Reference [1] M. Jeong et al, “Fast Active Scan for Measurement and Handoff,” IEEE 802.11-03/416r0 [2] M. Jeong et al, “Fast Active Scan Proposal,” IEEE 802.11-03/623r0 [3] J. Spilman et al, “Test Methodology for Measuring BSS Transition Time,” IEEE 802.11-04/0748r1 [4] M. Rudolf et al, “802.11 Discovery Phase and Passive Scanning Mode,” IEEE 802.11-04/0718r0 [5] E. Hepworth et al, “IETF Network Discovery and Selection Overview,” IEEE 802.11-04/1020r0 [6] J. Arkko et al, “Network Discovery and Selection Problem,” draft-ietf-eap-netsel-problem-01.txt [7] F. Adrangi et al, “Identity Selection Hits for Extensible Authentication Protocol (EAP),” draft-adrangi-eap-network-discovery-03.txt Fujio Watanabe, DoCoMo USA Labs