WLAN Paging and Idle Mode Month Year Sept 2006 November 2006 WLAN Paging and Idle Mode Authors: Date:2006-11-16 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>. Emily Qi et al Emily Qi et al

Month Year Sept 2006 November 2006 Abstract This document describes Idle Mode and WLAN Paging normative text proposal (doc 06/0943r6) in support of the Power Saving objective, REQ2010. What’s new compared to doc 06/0943r5 Added Paging Service Protection for Idle Mode Request/Response Changed Paging Domain to Mobility Domain and aligned Paging Server with PMK-R1 key holder Included additional updates to improve the draft Emily Qi et al Emily Qi et al

Agenda Motivation Idle Mode and Paging Concepts Month Year Sept 2006 November 2006 Agenda Motivation Idle Mode and Paging Concepts Protocol Overview and Feature Summary Power Consumption Comparison Emily Qi et al Emily Qi et al

Month Year Sept 2006 November 2006 Motivation Extend battery standby hours for handheld and ultra mobile devices to support applications such as VoIP over WLAN Additional benefits Reduce the network load (wired/wireless) required for BSS transition Preserve resources (memory, etc) used to maintain connectivity with associated idle STAs Emily Qi et al Emily Qi et al

Power Consumption Issues Month Year Sept 2006 November 2006 Power Consumption Issues Awake time at DTIM and Listen interval Overhearing broadcast/unicast messages at Rx Unnecessary BSS transitions while roaming Scanning Overhead OS wakes up to call supplicant Key Derivations: PMKR1 and PTK Exchange of Authentication and Reassociation messages Emily Qi et al Emily Qi et al

Unnecessary BSS Transition Scenario Month Year Sept 2006 November 2006 Unnecessary BSS Transition Scenario BSS Transition Data packets Emily Qi et al Emily Qi et al

Introducing Idle Mode and Paging Month Year Sept 2006 November 2006 Introducing Idle Mode and Paging Idle Mode: save power and resources STA enters “deep sleep” if there is no outgoing/incoming traffic If STA roams out of the coverage area of the last known associated AP, STA doesn’t need to reassociate with a new AP when it is in “idle mode” Paging: wake STA and avoid packet loss Infrastructure will “page” the client if there is incoming traffic STA wakes up at a longer “sleep” interval to check for incoming frame, and STA will associate with an AP when it receives the “paging” Emily Qi et al Emily Qi et al

Paging Concepts and Logical Entities Month Year Sept 2006 November 2006 Paging Concepts and Logical Entities Paging Group (PG) - a group of APs in which STA can be paged A Mobility Domain comprises one or more Paging Groups A STA must reassociate if it transitions to an AP in a different Paging Group Paging Server Provides Paging Services and Paging key management Serves one or more Paging Groups Emily Qi et al Emily Qi et al

Example of WLAN Paging Architecture Month Year Sept 2006 November 2006 Example of WLAN Paging Architecture Paging group #1 Mobility Domain Paging Server #1 (PMK-R1 key holder, aka AP Controller) Paging Server #2 (PMK-R1 key holder, aka AP) Paging group #3 Paging group #2 Emily Qi et al Emily Qi et al

Month Year Sept 2006 November 2006 Protocol Overview Paging Capability and Service Discovery (Beacon/Probe Response) Idle Mode Request (STAAP) and Response (APSTA) frames Enter Idle Mode Exit Idle Mode Idle Mode Update for Keep-alive update Paging Indication element Included in the Beacon frame at Paging Interval Included in the Probe Response frame as per STA requests Emily Qi et al Emily Qi et al

Paging Advertising and Discovery Month Year Sept 2006 November 2006 Paging Advertising and Discovery Wireless Network Management Capability element Paging bit is set to 1 to indicate that Paging service is enabled by AP or STA B0 B1 B2 B3 B4 B5 B6 B7 B15 Multicast Event Log Diagnostics Presence FBMS Proxy ARP Service Paging Reserved Bits: 1 9 Paging Information element Advertise Paging Service and Paging Indication delivery information in Beacon and Probe Response Element ID Length Paging Service ID Paging Group ID Paging Interval DPIM Count Octets: 1 6 Emily Qi et al Emily Qi et al

Paging Indication and Paging Interval Month Year Sept 2006 November 2006 Paging Indication and Paging Interval Paging Indication element Element ID Length Page Bitmap Control Partial Virtual Bitmap Octets: 1 1– 251 Bit number N is 0 if there are no paging for the station whose Paging ID is N. If any paging notification for that station arrives at the Paging Server, bit number N in the page-indication virtual bitmap is 1. Frames containing Paging Indication: Beacon only when DPIM count is 0 Probe Response Emily Qi et al Emily Qi et al

Idle Mode Request/Response Month Year Sept 2006 November 2006 Idle Mode Request/Response Idle Mode Request element Element ID Length Request Type STA Address Paging Server ID Group Octets: 1 6 Request Type: Enter Idle Mode, Update Idle Mode, and Exit Idle Mode Idle Mode Response element Element ID Length Response Status STA Address Paging Server Group Keep-alive Timer Octets: 1 6 2 Request Type: Enter Idle Mode and Update Idle Mode Emily Qi et al Emily Qi et al

Paging Service Key Hierarchy Month Year Sept 2006 November 2006 Paging Service Key Hierarchy Paging Service Pairwise Master Key (PSMK) is derived from PMK-R0 Paging Service Temporal Key (PSTK) is used to protect Idle Mode Request and Idle Mode Response Message from forgery Emily Qi et al Emily Qi et al

Example of Message Flow Month Year Sept 2006 November 2006 Example of Message Flow Emily Qi et al Emily Qi et al

Example: Idle Mode and Paging Scenario Month Year Sept 2006 November 2006 Example: Idle Mode and Paging Scenario SIP_INVITE (for STA1) Paging Group 1 Paging Group 2 Paging Exit Idle Mode Paging Server (PMK-R1 key holder, aka AP controller) Paging Request Enter Idle Mode BSS transition Enter Idle Mode Data packets Idle Mode messages Emily Qi et al Emily Qi et al

Feature Summary Idle Mode extends mobile device standby time Month Year Sept 2006 November 2006 Feature Summary Idle Mode extends mobile device standby time Paging Service wakes STA to receive incoming traffic Paging Group provides bandwidth efficiency and scalability Paging Service Protection provides forgery protection for Idle Mode Request/Response frame contents Emily Qi et al Emily Qi et al

Power Consumption Analysis Month Year Sept 2006 November 2006 Power Consumption Analysis Emily Qi et al Emily Qi et al

Use Case and Modes Considered November 2006 Use Case and Modes Considered Use Case The STA is on standby (i.e., it has no data to send/receive) The STA roams between APs The STA keeps the required state and/or connectivity to be ready to receive/transmit data whenever required The percentage of time it has to be “awake” or active to meet the above requirement is estimated Modes Considered Legacy PSM STAs wake up at Listen Interval to check for unicast These STAs are typically not interested in multicast/broadcast Roaming requires re-association Paging Mode (Our Proposal) Emily Qi et al

Assumption The number of roam (s) = 0 – 30 BSS transitions per hour Month Year Sept 2006 November 2006 Assumption The number of roam (s) = 0 – 30 BSS transitions per hour Assuming walking speed: 1.1m/s; a walking user walks out of an AP cell in 30-90 seconds, depending on the AP coverage. The result is 120 – 40 transitions per hour respectively for a walking user. Wake up interval Legacy Listen : 20 beacon intervals Paging Mode : 20 beacon intervals Roaming awake time Legacy PSM = 100 – 800 ms of stay awake time (due to OS wakeup/scanning/re-association/re-authentication) Paging Mode = 10 – 150 ms of stay awake time (scanning/PIM processing) Periodic background scanning time = 50ms - 500 ms with 1 scanning per min Power consumption = awake-time * active-power-consumption + idle-time * idle-power consumption Awake-time = (the number of wake-up interval * 2ms) + (the number of scans * scanning-time) + (roaming awake time)* the number of roams Emily Qi et al Emily Qi et al

Month Year Sept 2006 November 2006 Paging Mode compared with Legacy PSM (Paging Mode w/o background scanning) 20% Battery capacity: 3200mA x 3.7V Emily Qi et al Emily Qi et al

Month Year Sept 2006 November 2006 Paging Mode compared with Legacy PSM (both modes w/ background scanning) 7% Battery capacity: 3200mA x 3.7V Emily Qi et al Emily Qi et al

Thank You! November 2006 Month Year Sept 2006 Emily Qi et al

Scanning Comparison while STA roaming Month Year Sept 2006 November 2006 Scanning Comparison while STA roaming Legacy STA Idle Mode STA Goals of Scanning Scanning for BSS Transition: Find the best AP to associate with Scanning to receive Paging Indication: Receive a beacon from any AP that belongs to the same paging domain Possible Actions 1.Scan all or many channels and measure the RSSI of Beacon or other parameters of each channel 2. Select the best AP 1. Stay with the same channel, and then switch to a valid channel, if required 2. STA will stop trying other channels once STA hears a beacon in the same PG Optimization Use .11k “Neighbor Report” to narrow down number of channels Use .11k “AP Channel Report” for the next channel scanning Average number of channels scanned ~3 for 2.4Ghz 0~1 Scanning time Assume a minimum wait of 10ms in the same channel, if no beacon, do active probing on a channel, average of 30ms (20ms for minimum channel time and 40ms for maximum channel time) 10ms (wait) + 30ms * (2 ~ 11) = 50ms ~ 500ms 10ms +30ms *(0~1)= 10ms ~40ms Emily Qi et al Emily Qi et al

Awake Time Comparison November 2006 Legacy STA Idle Mode STA Month Year Sept 2006 November 2006 Awake Time Comparison Legacy STA Idle Mode STA WNIC periodically wakes up at DTIM or at Listen Interval at Paging interval NIC Wake up time for Roaming time Scanning + authentication/association = (70ms ~190ms) + (30ms ~210ms) = 100ms ~ 400ms Scanning + Sync = (10ms ~100ms) + 0 ~ 50 = 10ms ~150ms NIC Total wake up time (per hour) =WT Assumption: Beacon interval = 100 TUs, DTIM = 2, Listen Interval = Paging Interval = 20 (2.048s); STA stays awake on average for 2 ms to receive and process a beacon (DTIM, Paging, TIM) from the home AP. Average background scans per hour = 60; n = # of roaming per hours, WT= [#of DTIMs *2ms OR #of Listen Intervals *2ms] + n*(130ms ~ 800ms) * periodic background scan awake time (60*(50ms~ 500ms) ) WT= [#of Paging Intervals *2ms] + n*(10ms ~150ms) OS awake time Calling supplicant, key derivation, and initiate/maintain network connection ~400ms, depending on device type: handheld, PDA, and UMPC 0 – potentially Emily Qi et al Emily Qi et al