1. WLAN Paging and Idle Mode
Month Year
Sept 2006
November 2006
WLAN Paging and Idle Mode
Authors:
Date:
Notice: This document has been prepared to assist IEEE 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
Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures < 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 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 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at
Emily Qi et al
Emily Qi et al

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

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

16. 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

17. 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

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

19. 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

20. 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 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 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

21. 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

22. 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

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

24. 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

25. 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