WLAN Handoff Scenarios Example handoffs with RRM measurements and network assistance

1. March 2003 doc: IEEE 802.11-03/225r0 WLAN Handoff ScenariosExample handoffs with RRM measurements and network assistance Joe Kwak InterDigital Communications Corporation Joe Kwak, InterDigital

2. Outline • WLAN Handoff Functional Model • Functional analysis with/without network assistance • Message Sequences for Autonomous H/O • Message Sequences with Network Assisted H/O • Open Issues Joe Kwak, InterDigital

3. H/O Yes Apply H/O Decision Algorithm Perform Handoff to New AP Select/Configure Measurements Perform Measurements H/O No WLAN H/O Functional Model • STA configures measurements and selects source Access Point (AP) from set of available neighbor APs. • STA configures cycle of neighbor measurements to continuously evaluate H/O options, continuously apply H/O decision algorithm. • When H/O is imminent, STA and network may prepare for scheduled H/O. • At H/O time, STA reassociates with destination AP. • AT H/O time, network source/target APs coordinate for IP reroute (IAPP) and data fragment routing. Figure 1. STA Functions for AP Handoff Joe Kwak, InterDigital

4. Scenario Goals • Demonstrate H/O functions in 802.11 terms (present and future) • Indicate use of inter-RAT measurements between 11a and 11b for 11g devices • Indicate method to track signal quality of neighbor APs • Indicate desire to coordinate “seamless” H/O • Indicate differences between STA autonomous H/O and network assisted H/O • Detail high level Message Sequence Charts for autonomous and network assisted H/O • Scenario details reveal use of example, simplistic H/0 decision algorithm. • Indicate H/O support items which are out of scope for TGK. Joe Kwak, InterDigital

5. 1 2 3 Scenario Functional Analysis 1. Initial association, using current methods, to select source AP. 2. Initial neighbor scanning to determine AP H/O options on all channels, all PHYs. Auto: Passive scan all, then active scan idle channels; optional Beacon Report indicating link quality/received power to AP. Net: AP sends Beacon_Scan_Request action frame to STA, Beacon Scan Report required. 3. Schedule continuous scan cycles. Use Power Save mode or NAV based non-contention periods to measure on other channels, on other PHYs. • Active PHY/Channels: short cycle period (20 second?), fast passive scan. • Auto: Continuous scanning with optional report cycle (1 minute?) with Beacon Report of all active PHY/channels. • Net: AP sends Beacon_Scan_Request with continuous scanning and periodic reporting (1 minute cycle?). Network may update neighbor list by reissuing Beacon_Scan_Request. • Inactive PHY/Channels: longer cycle period (5 min?), slower active scan. Active scan results used to update active PHY/channels list. Active scanning may only be initiated when number of active PHY/channels falls below threshold. Joe Kwak, InterDigital

6. Cross H/O Thresh 4 Signal quality AP 1 AP 3 AP 4 AP 5 Time H/O trigger Scenario Functional Analysis (2 of 3) • 4a. Auto: Schedule continuous handoff decision evaluation. • Continuous statistics update with each beacon scan: • PSNI: LastVal, AverageVal, Variance, Trend. • RCPI: LastVal, AverageVal, Variance, Trend. • Apply H/O decision threshold after each beacon scan. • When H/O criteria are met, send H/O_Prep_Request. H/O Hysteresis Cell load factor AP1--->AP5 Joe Kwak, InterDigital

7. 4 5 Scenario Functional Analysis (3 of 3) • 4b. Net: Schedule continuous handoff decision evaluation. • AP Updates neighbor list and provides cell load factors by reissuing Beacon_Scan_Request with continuous scanning and periodic reporting. • AP requests continuous measurement of STA’s UL load factor with periodic reporting. • STA may receive H/O_Prep_Request action frame from AP at any time. • STA may send H/O_Prep_Request action frame to AP at any time. • Cell load factor may be used to prevent H/O to certain or all cells. • 5. Execute Synchronized_Handoff_Request Procedure • Source AP coordinates H/O with target AP. IP reroute for H/O is prepared at H/O_Prep time. Context transfer is prepared. Make-before-break switch? • Target AP pre-allocates required resources for STA. • Target AP may pre-authenticate, pre-authorize STA??? • At H/O time, source AP reroutes IP for STA to target AP, transfers STA context. • At H/O time, STA changes PHY/channel and reassociates with target AP. • After H/O time, source AP forwards any undelivered data segments to target AP if decryption is still possible. • After H/O time, target AP reauthenticates and reauthorizes STA and reestablishes services with minimal (??) interuption. Joe Kwak, InterDigital

8. Beacon_Scan_Request[NL] Power_Save_OFF Association_Request Power_Save_ON Power_Save_On Power_Save_OFF Power_Save_On Power_Save_OFF Power_Save_OFF Power_Save_On Beacon_Scan_Report Beacon_Scan_Response Power_Save_Ack Power_Save_Ack Power_Save_Ack Power_Save_Ack Power_Save_Ack Power_Save_Ack Power_Save_Ack Association_Response Power_Save_Ack Listen/Probe Chan 1 Listen/Probe Chan1 Listen/Probe Chan 1 Listen/Probe Chan 1 Listen/Probe Chan n Beacon or Probe Response Beacon or Probe Response Beacon or Probe Response Beacon or Probe Response Beacon or Probe Response 1 3 4 2 Optional Message Beacon_Scan_Report Autonomous H/O Scenario Message Sequence Chart(1 of 2) AP1-n STA APsource Initial Neighbor Scan: 1. Passive scan all 11a chans 2. Active scan all inactive 11a chans 3. Passive scan all 11b chans 4. Active scan all inactive 11b chans 5. Off-channel scans not to interfere with ongoing services Schedule Beacon Scans Continuous Scan Cycles: 1. Short cycle active neighbor scans 2. Long cycle inactive chans 3. Update short/long PHY/chan lists 4. Apply H/O criteria after each short cycle scan 5. Off-channel scans not to interfere with ongoing services Joe Kwak, InterDigital

9. Reassociate_Response 5 Reassociate_Request Autonomous H/O Scenario Message Sequence Chart(2 of 2) AP1-n STA APsource When H/O criteria are met: - STA may optionally notify APsource for scheduled H/O, or - STA reassociates without scheduling. - If unscheduled H/O, APtarget uses IAPP to transfer context and reroute. - If scheduled, APtarget and APsource coordinate at scheduled time. H/O threshold crossed H/O_Prep_Request[Apx,T] H/O_Prep_Response H/O_Prep_Request[Apx,T] H/O_Prep_Response at time=T IAPP_Reassociate H/O_Complete_Request H/O_Complete _Response Joe Kwak, InterDigital

10. STA Power_Save_OFF Power_Save_ON UL_Load_Report Power_Save_On Power_Save_OFF UL_Load_Report Beacon_Scan_Response Power_Save_OFF Beacon_Scan_Report Beacon_Scan_Response Beacon_Scan_Report Beacon_Scan_Report UL_Load_Report UL_Load_Report Power_Save_On Beacon_Scan_Report Power_Save_Ack Beacon_Scan_Request[NL] UL_Load_Request NL&CellLoad_Info Power_Save_Ack Power_Save_Ack Power_Save_Ack Power_Save_Ack NL&CellLoad_Info Power_Save_Ack Listen/Probe Chan n Listen/Probe Chan 1 Listen/Probe Chan 1 Listen/Probe Chan1 Beacon or Probe Response Beacon or Probe Response Beacon or Probe Response Beacon or Probe Response 2 4 3 Network Assisted H/O Scenario Message Sequence Chart (1 of 2) NM AP1-n APsource Initial Neighbor Scan: same as Auto Beacon_Scan_Report Beacon_Scan_Request[NL,Load,Hyst] Schedule Beacon Scans Continuous Scans, H/O Eval: same as Auto but with NM supplied Cell Loads and Hysteresis for H/O evaluation Joe Kwak, InterDigital

11. Reassociate_Response H/O_Complete_Request 5 H/O_Complete _Response Reassociate_Request Network Assisted H/O Scenario Message Sequence Chart (2 of 2) NM AP1-n STA APsource When H/O criteria are met: - STA will notify APsource for scheduled H/O, or - NM will notify APsource for scheduled H/O. -All H/Os are scheduled. H/O threshold crossed H/O threshold crossed OR H/O_Prep_Request[Apx,T] H/O_Prep_Request[Apx,T] H/O_Prep_Response H/O_Prep_Request[Apx,T] H/O_Prep_Request[Apx,T] H/O_Prep_Request[Apx,T] H/O_Prep_Response at time=T Joe Kwak, InterDigital

12. New Items Needed to Support Handoff Scenarios • Action frame to perform Beacon_Scan_Request periodic measurements including: • short passive scan cycle of known neighbors (NL), periodic scan report • long active scan cycle on other channels, immediate beacon report on probe response • Supply STA hysteresis value for H/O decision • Supply Cell Loading factors for NL cells for H/O decision. • Measurement Report frame to provide Beacon_Scan_Report • Action frame for measurement of UL_load in STA. • Measurement Report frame to provide UL_Load_Report • Action frame for scheduled H/O_Preparation with APtarget, scheduled time for handoff, and other parameters. • Modifications to IAPP to support scheduled H/O • Action frame to perform H/O_Complete exchange to complete scheduled context transfer and to transfer any remnant data segments. • Network Manager (NM) access to Beacon_Scan_Report measurement data. • NM provision of Cell Load Factors and Hysteresis for H/O evaluation. Items in red are out of scope for TGK Joe Kwak, InterDigital

13. Open Issues • TGK is addressing only half of the 802.11 specification changes for Handoff: the RRM measurement and reporting portion [STA-->Higher Layer Applications]. • The network assistance interface to provide new H/O decision parameters [HL Applications-->STA] are out of scope for TGK. • Efforts are needed in WNG committee to initiate SG to begin work to complete this handoff interface. • Parallel efforts are underway at 802-level for Handoff Interface guidelines and may affect 802.11 and TGK. • ?Strawpoll to assess level of interest in starting now? Joe Kwak, InterDigital