Fast Active Scan Proposals May 2003 doc.: IEEE 802.11-03/xxxr0 July 2003 Fast Active Scan Proposals Moo Ryong Jeong, Fujio Watanabe, Toshiro Kawahara DoCoMo USA Labs mrj@ieee.org Zhun Zhong Philips zhun.zhong@philips.com Moo Ryong Jeong, DoCoMo USA Labs. Moo Ryong Jeong, DoCoMo USA Labs.

May 2003 doc.: IEEE 802.11-03/xxxr0 July 2003 Background 03/416r0 presented an active scanning scheme having short scanning time* 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 The cost of the short scanning time is increased implementation complexity Moo Ryong Jeong, DoCoMo USA Labs. Moo Ryong Jeong, DoCoMo USA Labs.

Goal of This Presentation July 2003 Goal of This Presentation This presentation provides: Three schemes (modification to 03/416r0) that make trade-off between scanning time and implementation complexity at different levels Moo Ryong Jeong, DoCoMo USA Labs.

Current Active Scanning Procedure July 2003 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 can hear and respond by sending probe response Moo Ryong Jeong, DoCoMo USA Labs.

Assumptions Changed STA may have knowledge on possible neighbor APs July 2003 Assumptions Changed STA may have knowledge on possible neighbor APs Site report, previous scanning results STA may be interested only in specific APs APs chosen from site report or previous scanning results Probe request can be a directed frame (by standard modification) to a desired AP so that the AP can hear and respond within SIFS We present fast active scanning methods which fits with changed assumptions Moo Ryong Jeong, DoCoMo USA Labs.

Basic Ideas of Fast Active Scan May 2003 doc.: IEEE 802.11-03/xxxr0 July 2003 Basic Ideas of Fast Active Scan Probe request is sent as directed frame to a specific AP on the AP’s operation channel with BSSID in DA field and BSSID field AP responds to directed probe request after SIFS Response may be a probe response or an ACK If the response is an ACK, AP sends probe response later STA can learn availability/unavailability of AP after SIFS If STA receives ACK, STA stay on the channel unlit it receives probe response Or PIFS Moo Ryong Jeong, DoCoMo USA Labs. Moo Ryong Jeong, DoCoMo USA Labs.

May 2003 doc.: IEEE 802.11-03/xxxr0 July 2003 Original scheme (03/416r0) AP sends probe response with broadcast destination address after SIFS deferral Probe response is fast transmitted with high probability of success Probe response considered as ACK to probe request No retransmission of probe response MinChannelTime Or PIFS Scanning Station Probe to APi APi P Response SIFS Moo Ryong Jeong, DoCoMo USA Labs. Moo Ryong Jeong, DoCoMo USA Labs.

Original scheme (03/416r0) Shortest scanning time May 2003 doc.: IEEE 802.11-03/xxxr0 July 2003 Original scheme (03/416r0) Shortest scanning time ≈ 10 sec when AP is unavailable SIFS plus transmission time of probe response ( 898 sec) when AP is avaiable Most demanding in implementation Or PIFS Moo Ryong Jeong, DoCoMo USA Labs. Moo Ryong Jeong, DoCoMo USA Labs.

Alternative Scheme 1 AP sends ACK after SIFS period July 2003 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 Moo Ryong Jeong, DoCoMo USA Labs.

Alternative Scheme1 Scanning time Least demanding in implementation July 2003 Alternative Scheme1 Scanning time For unavailable AP, as short as in 03/416r0 For available AP, longer than 03/416r0 but shorter than conventional active scanning (collocated APs do not respond to probe request) Least demanding in implementation Moo Ryong Jeong, DoCoMo USA Labs.

Alternative Scheme 2 AP sends ACK after SIFS period July 2003 Alternative Scheme 2 AP sends ACK after SIFS period When probe response is ready, send it with PIFS deferral Facilitates fast and safe transmission of probe response Probe response is retransmitted with DIFS and random backoff unless ACK is received MaxChannelTime MinChannelTime Scanning Station Probe to APi Ack APi Ack Other frames P Response SIFS SIFS PIFS Moo Ryong Jeong, DoCoMo USA Labs.

Alternative Scheme 2 Scanning time July 2003 Alternative Scheme 2 Scanning time For unavailable AP, as short as in 03/416r0 For available AP, longer than 03/416r0 but shorter than alternative scheme 1 (priority access of probe response) Less demanding than 03/416r0 but more demanding than alternative scheme 1 Moo Ryong Jeong, DoCoMo USA Labs.

Knowledge on Neighbor AP July 2003 Knowledge on Neighbor AP Collection of neighbor AP information Offline collection by operator Realtime collection by AP Reassociation message (TGf) Beacon report from associated STAs (TGk) Exchange neighbor AP information among access point Realtime collection by STA Results from previous scanning (passive or conventional active) Delivery of neighbor AP information Initial setup Site Report request Beacon Probe response Moo Ryong Jeong, DoCoMo USA Labs.

Indicating Probe Request with Fast Active Scan July 2003 Indicating Probe Request with Fast Active Scan Use current probe request AP’s MAC address in DA and BSSID fields in probe request as indication of fast active scan Define new management frame subtype for probe request with fast active scan Define new action category for probe request with fast active scan Moo Ryong Jeong, DoCoMo USA Labs.

Indicating Fast Active Scanning Capability of AP July 2003 Indicating Fast Active Scanning Capability of AP Require all STAs capable of radio measurement be also capable of fast active scanning Set B12 (radio measurement) in capability information field Non-AP STA shall be compatible with all schemes AP shall implement at least one of the three schemes Implementation changes according to the fast active scanning needs Define new bit in capability information field to indicate fast active scanning capability Moo Ryong Jeong, DoCoMo USA Labs.

Modification Required July 2003 Modification Required Addressing Directed frame for probe request (all schemes) Broadcast frame for probe response (03/416r0) IFS SIFS between probe request and probe response (03/416r0) PIFS deferral in sending probe response (alternative 2) ACK Immediate probe response considered as ACK to probe request (03/416r0) MaxChannelTime Ignored if probe response is received Moo Ryong Jeong, DoCoMo USA Labs.

Conclusion We considered improvement of active scanning May 2003 doc.: IEEE 802.11-03/xxxr0 July 2003 Conclusion We considered improvement of active scanning Our schemes speed up active scanning process when there is prior knowledge on neighbor APs (e.g. site report) Proposed active scanning schemes are effective for: Reducing overhead in active scan-based measurement Fast handoff AP implements one of the three schemes according to the fast active scanning needs Moo Ryong Jeong, DoCoMo USA Labs. Moo Ryong Jeong, DoCoMo USA Labs.