1. WLAN Paging and Idle Mode
Month Year
Sept 2006
Sept 2006
WLAN Paging and Idle Mode
Authors:
Date:
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Emily Qi et al
Emily Qi et al

2. Month Year
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Abstract
This document describes WLAN Paging and Idle normative text proposal (doc#06/0943r5) in support of Power Saving objective in accordance with REQ2010.
What’s new:
Removed Paging Service Protection
Use the Paging Virtual Bitmap for Paging Indication
Changed the mechanism used to broadcast the Paging Indication from the Action Frame to the Beacon frame
Included additional updates to improve the draft
Emily Qi et al
Emily Qi et al

3. Agenda Power Saving Goal Power Consumption Issues
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Agenda
Power Saving Goal
Power Consumption Issues
Idle Mode Concepts and Protocols
Power Consumption Comparison
Emily Qi et al
Emily Qi et al

4. Month Year
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Sept 2006
Power Saving Goal
Extend standby hours for handheld and Ultra Mobile Devices to support applications such as VoIP over WLAN
Emily Qi et al
Emily Qi et al

5. Power Consumption Issues
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Sept 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
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Sept 2006
Unnecessary BSS Transition Scenario
BSS Transition
Data packets
Emily Qi et al
Emily Qi et al

7. Introducing Idle Mode and Paging
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Sept 2006
Introducing Idle Mode and Paging
Idle Mode : STA enters “deep sleep” if there is no outgoing/incoming traffic
STA wakes up at a longer “sleep” interval to check if there is any incoming frame
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”
WLAN Paging: Infrastructure will “page” the client if there is incoming traffic
STA will be active when it receives the notification of incoming traffic from the infrastructure
Emily Qi et al
Emily Qi et al

8. Idle Mode Operation & Paging Concepts
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Sept 2006
Idle Mode Operation & Paging Concepts
Idle Mode Operation
Paging Capability Discovery and Advertisment
STA Enters Idle Mode
APs broadcasts Paging Indications, and STA wakes up to receive paging indication
STA Exits Idle Mode
Paging concepts and logical entities
Paging Domain (PD) - a set of BSSs within the same ESS
Paging Server - provides Paging Services
Can be in the AP/controller or a separate network entity
Paging Group (PG) - a group of APs in which STA can be paged
A Paging Domain comprises one or more Paging Groups
Emily Qi et al
Emily Qi et al

9. Idle Mode and Paging Protocol
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Sept 2006
Idle Mode and Paging Protocol
Paging Capability and Service Discovery (Beacon/Probe Response)
Idle Mode Request (STAAP) and Response (APSTA)
Enter Idle Mode
Exit Idle Mode
Idle Mode Update for Paging Group ID and Keep-alive
Paging Indication
Beacon at Paging Interval
Probe Response as STA requests
Emily Qi et al
Emily Qi et al

10. Paging Advertising and Discovery
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Sept 2006
Paging Advertising and Discovery
Wireless Network Management Capability element
AP/ STA exchange Paging capability
Paging bit is set to 1 to indicate that Paging service is enabled by AP or STA B0 B1 B2 B3 B4 B5
B15
Multicast
Event Log
Diagnostics
Presence
Paging
Reserved
Bits: 1 11
Paging Information element
Advertise Paging Service and Paging Indication delivery information and Present in Beacon and Probe Response
Element ID
Length
Paging
Domain ID
Paging Service ID
Paging Group ID
Paging Interval
DPIM Count
Octets: 1 6 2
Emily Qi et al
Emily Qi et al

11. Paging Indication and Paging Interval
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Sept 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

12. Idle Mode Request/Response
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Sept 2006
Idle Mode Request/Response
Idle Mode Request element
Element ID
Length
Request
Type
STA Address
Paging
Domain ID
Server
Group
Octets: 1 6
Request Type: Enter Idle Mode, Update Idle Mode, and Exit Idle Mode
Idle Mode Response element
Element ID
Length
Response
Type
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

13. Message Flow Sept 2006 Month Year Sept 2006 Emily Qi et al

14. Example: Roaming with Idle Mode Scenario
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Sept 2006
Example: Roaming with Idle Mode Scenario
Paging Group 1
Paging Group 2
Paging
Exit Idle Mode
Paging Server
Idle Mode Update (Paging Group update)
BSS transition
Enter Idle Mode
Data packets
Idle Mode messages
Emily Qi et al
Emily Qi et al

15. Feature Summary Idle mode operation extends a STA standby time
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Sept 2006
Feature Summary
Idle mode operation extends a STA standby time
WLAN paging wakes up the STA to receive incoming traffic
The Paging Group provides bandwidth efficiency and scalability
A Paging Server can be used for deployment flexibility and scalability
Emily Qi et al
Emily Qi et al

16. Power Consumption Comparison
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Sept 2006
Power Consumption Comparison
Emily Qi et al
Emily Qi et al

17. Scanning Comparison while STA roaming
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Sept 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
~2 for 2.4Ghz
~6 for 5.0Ghz
0~3
Scanning time
Assume a minimum wait of 10ms in the same channel, if no beacon, do active probing on a channel, average of 30ms.
10ms (wait) + 30ms * (2~6)
= 70ms ~190ms
10ms +30ms *(0~3)= 10ms ~100ms
Emily Qi et al
Emily Qi et al

18. Awake Time Comparison Sept 2006 Legacy STA Idle Mode STA
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Sept 2006
Awake Time Comparison
Legacy STA
Idle Mode STA
WNIC periodically wakes up
at DTIM and 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 minute) =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*(100ms ~ 400ms)
+periodic background scanning ((50ms~500ms) * 60)
WT= [#of DTIMs *2ms OR #of Listen Intervals *2ms] + n*(10ms ~150ms)
OS awake time
- calling supplicant, key derivation, and initiate/maintain network connection
- depending on device type: handheld, PDA UMPC, Laptop
0 – potentially
Emily Qi et al
Emily Qi et al

19. WNIC Awake Time Comparison
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Sept 2006
WNIC Awake Time Comparison
Periodic background scanning overhead added to legacy power-save
Average minimum overhead per scan = 50 ms
Average maximum overhead per scan = 500 ms
Average scans per hour = 60
Emily Qi et al
Emily Qi et al

20. Month Year
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Sept 2006
Conclusions
The “Awake Time” in legacy power-save is compared with that of idle mode
The actual power consumption may vary depending on whether the STA is transmitting or receiving or idle when awake
Awake-time in idle-mode 2 – 10 times better than legacy depending on how frequently STAs roam
The actual power-consumption benefits may be much higher as idle mode operations may be implemented without OS intervention
Reduce OS Power Consumption will be significant
Detail is not considered in the analysis.
Emily Qi et al
Emily Qi et al

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