January 2003 Joe Kwak InterDigital Communications Corporation IEEE 802.11-03/100r1 doc: IEEE 802.11-03/225r0 March 2003 WLAN Handoff Scenarios Example handoffs with RRM measurements and network assistance Joe Kwak InterDigital Communications Corporation Submission Joe Kwak, InterDigital

Outline WLAN Handoff Functional Model January 2003 IEEE 802.11-03/100r1 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 Submission

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. Select/Configure Measurements Perform Apply H/O Decision Algorithm Handoff to New AP H/O Yes No Figure 1. STA Functions for AP Handoff Joe Kwak, InterDigital Submission

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 Submission

Scenario Functional Analysis 1 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. 2 3 Joe Kwak, InterDigital Submission

Scenario Functional Analysis (2 of 3) 4 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. Cross H/O Thresh H/O trigger Signal quality Time AP 3 AP 1 AP 4 AP 5 H/O Hysteresis Cell load factor AP1--->AP5 Joe Kwak, InterDigital Submission

Scenario Functional Analysis (3 of 3) 4 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. 5 Joe Kwak, InterDigital Submission

Autonomous H/O Scenario Message Sequence Chart (1 of 2) AP1-n STA APsource Association_Request 1 Association_Response Beacon_Scan_Request[NL] Beacon_Scan_Response 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 Power_Save_ON Power_Save_Ack Listen/Probe Chan1 Beacon or Probe Response 2 Listen/Probe Chan n Beacon or Probe Response Power_Save_OFF Power_Save_Ack Beacon_Scan_Report Schedule Beacon Scans 3 Listen/Probe Chan 1 Beacon or Probe Response Power_Save_On Power_Save_Ack Power_Save_OFF 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 Listen/Probe Chan 1 Beacon or Probe Response Power_Save_On Power_Save_Ack Power_Save_OFF 4 Listen/Probe Chan 1 Beacon or Probe Response Power_Save_On Power_Save_Ack Power_Save_OFF Beacon_Scan_Report Optional Message Joe Kwak, InterDigital Submission

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 Reassociate_Request 5 Reassociate_Response IAPP_Reassociate H/O_Complete_Request H/O_Complete _Response Joe Kwak, InterDigital Submission

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

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 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 5 at time=T Reassociate_Request Reassociate_Response H/O_Complete_Request H/O_Complete _Response Joe Kwak, InterDigital Submission

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 Submission

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 Submission