AP Scanning Date: 2004-12-18 Authors: January 2005 January 2005 doc.: IEEE 802.11-yy/xxxxr0 January 2005 AP Scanning Date: 2004-12-18 Authors: Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair <stuart.kerry@philips.com> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <patcom@ieee.org>. F.Watanabe et al, DoCoMo USA Labs F.Watanabe et al, DoCoMo USA Labs

Background Channel Scanning is a time-consuming process January 2005 Background Channel Scanning is a time-consuming process Passive scan: several beacon intervals per channel (e.g., >100ms) Active scan: 15 msec per channel Direct Probe Request is defined or not defined? M. Lefkowitz, “Directed probe request clarification,” IEEE802.11-03/833r0 F.Watanabe et al, DoCoMo USA Labs

Channel Scanning Time Scanning time represents January 2005 doc.: IEEE 802.11-yy/xxxxr0 January 2005 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 F.Watanabe et al, DoCoMo USA Labs F.Watanabe et al, DoCoMo USA Labs

SSID Overlapping SSID can be set to any value SSID: January 2005 SSID Overlapping 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 F.Watanabe et al, DoCoMo USA Labs

Critical for Voice Applications January 2005 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 F.Watanabe et al, DoCoMo USA Labs

Unicast Probe Request January 2005 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 F.Watanabe et al, DoCoMo USA Labs

January 2005 Proposed Changes Allow STA to send directed probe request during the handoff process only. AP shall reply with ACK and/or send the probe response later, or if capable, may reply with probe response within SIFS (similar to PS-Poll) delete F.Watanabe et al, DoCoMo USA Labs

Advantages Short Scanning Time Filter out APs with same SSID January 2005 Advantages Short Scanning Time Filter out APs with same SSID Conventional active scan Fast active scan Long preamble 1 Mbps Short preamble 2 Mbps When AP is unavailable MinChannelTime ( 670 sec) MinChannelTime ( 10 sec) When AP is available MaxChannelTime ( 15 msec) SIFS + time for sending probe response (= 586 ~ 898 sec) † (= 298 ~ 454 sec) † *: Excludes time for sending probe request †: Varies depending on the size of SSID field and Supported Rates field F.Watanabe et al, DoCoMo USA Labs

Alternative Scheme 1 January 2005 AP sends ACK after SIFS period Ack MinChannelTime Scanning Station Probe to APi APi Ack SIFS F.Watanabe et al, DoCoMo USA Labs

Alternative Scheme 2 January 2005 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 F.Watanabe et al, DoCoMo USA Labs

January 2005 doc.: IEEE 802.11-yy/xxxxr0 January 2005 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) F.Watanabe et al, DoCoMo USA Labs F.Watanabe et al, DoCoMo USA Labs

January 2005 Reference [1] M. Lefkowitz, “Directed probe request clarification,” IEEE802.11-03/833r0 [2] M. Jeong et al, “Fast Active Scan for Measurement and Handoff,” IEEE 802.11-03/416r0 [3] M. Jeong et al, “Fast Active Scan Proposal,” IEEE 802.11-03/623r0 [4] J. Spilman et al, “Test Methodology for Measuring BSS Transition Time,” IEEE 802.11-04/0748r1 [5] M. Rudolf et al, “802.11 Discovery Phase and Passive Scanning Mode,” IEEE 802.11-04/0718r0 [6] E. Hepworth et al, “IETF Network Discovery and Selection Overview,” IEEE 802.11-04/1020r0 [7] J. Arkko et al, “Network Discovery and Selection Problem,” draft-ietf-eap-netsel-problem-01.txt [8] F. Adrangi et al, “Identity Selection Hits for Extensible Authentication Protocol (EAP),” draft-adrangi-eap-network-discovery-03.txt F.Watanabe et al, DoCoMo USA Labs