AP Power Down Notification

1. AP Power Down Notification Authors: Date: 2008-07-15 Allan Thomson, Cisco Systems

2. Abstract Enterprise customers want to control when their AP network is active and when it is powered down to save energy costs This proposal shows a mechanism for the AP network to communicate to clients when one or more APs will be powered down Allan Thomson, Cisco Systems

3. The problem… • Enterprise customers will schedule shutdown of one or more APs in the network during off-peak hours • Example: Banking institutions with strict working hours do not require active wireless network outside of banking hours • The issue is that STAs are not aware of this shutdown and therefore will continuously scan looking for alternate networks to associate with • At the time of power down it is expected STAs are low mobility devices (i.e. unattended) • Handhelds, Laptops, Desktop, Printers, Copiers • Most devices will be plugged in • Upon shutdown of infrastructure, dual interface STAs may have alternate network connectivity (i.e. enet interface) Allan Thomson, Cisco Systems

4. The solution… • Provide a mechanism for the AP network to notify STAs that one or more APs will be shutdown for an extended period of time • Therefore allowing the STA to choose whether or not to take advantage of this knowledge to save power itself Allan Thomson, Cisco Systems

5. Use Case #1: Entire Floor Shutdown Allan Thomson, Cisco Systems

6. Use Case #2: Partial Floor Shutdown Allan Thomson, Cisco Systems

7. Use Case #3: Exception Handling Allan Thomson, Cisco Systems

8. Solution Details • Two options to update existing features… • Solution #1: BSS Transition Management • TGv feature • Solution #2: Neighbor Report • TGk feature Allan Thomson, Cisco Systems

9. Solution #1: Protocol Details • Modify BSS Transition Management Request Frame to indicate power down information • Frame may be sent individually addressed or group addressed • New Power Down Duration field • A 2 octet unsigned integer that represents the number of minutes the APs specified in the candidate list are going to be shutdown for • Field is reserved if value 0 • If the candidate list is empty then all APs in the ESS will be shutdown for the duration • A STA may choose to sleep for Power Down Duration Allan Thomson, Cisco Systems

10. Solution #1: Modified Request Mode • Additional bit added to Request Mode field • Power Down bit indicates the STA may take notice of the Power Down Duration field Allan Thomson, Cisco Systems

11. STAs may be send a BSS Transition Management Response frame in response to a BSS Transition Management Request frame Two new status codes 1) Allows a STA to indicate to the AP that it requests the AP remains active 2) Allows a STA to indicate to the AP that it requests a delay in the shutdown by X minutes STA would provide power down delay parameter in addition to status code AP policy (beyond scope) may choose to accept or deny STA’s request New Status code value as indicated Solution #1: Power Down Response Allan Thomson, Cisco Systems

12. Solution #2: Protocol Details • Neighbor Report Request frame introduced in 11k • Solution #2 will • A) Add Neighbor Report information element to the Neighbor Report Request frame • B) Modify Neighbor Report element to indicate power down information element in the optional sub-element list as part of the Neighbor Report element • C) Define procedures to allow a STA to respond differently to the neighbor request if related to a power down vs non-power-down • i.e. If power down then the STA must respond with the list of neighbors it wants to keep alive Allan Thomson, Cisco Systems

13. Solution #2: Power Down Sub-Element • Add optional sub-element to indicate power down information • Sub-element ID: 72 • Name: Power Down • A 2 octet unsigned integer that represents the number of minutes the APs specified in the candidate list are going to be shutdown for • If the candidate list is empty then all APs in the ESS will be shutdown for the duration Allan Thomson, Cisco Systems

14. Solution #2: Power Down Response • Neighbor Report information element return in the Neighbor Report Response frame would include additional sub-element for Power Down Response • Add sub-element to indicate power down response information • Sub-element ID: 73 • Name: Power Down Response • A status code field that indicates accept or denied response (similar values to BSS Transition response for power down) • A 2 octet unsigned integer that represents the number of minutes the STA requests the AP remains awake Allan Thomson, Cisco Systems

15. BSS Transition and Neighbor List Synchronization • As APs shutdown the list of available APs must be synchronized with the neighbor reports AND transition management • Regardless whether Solution #1 or Solution #2 is chosen, both features will be impacted by APs disappearing off the network • If BSS Transition Management is used to communicate active power down, Neighbor lists will be updated once power down is complete • If Neighbor Request/Report frames are used then BSS Transition management will be affected Allan Thomson, Cisco Systems

16. Client Impact #1 • Problem – what happens if a client goes to sleep for the period notified but then a user moves the device to a region where a network is active and the user wants to access the network • Solution #A – Add a motion sensor to the device that reactivates the network scanning behavior after motion is detected • Solution #B – Add a user interface that indicates to the user the network has gone to “green-sleep” and prompts them to reactivate upon demand. • Solution #C – Use out-of-band sensor/receiver in handheld to indicate device has entered an area of network that has been shutdown • ALL above are out of scope of proposal Allan Thomson, Cisco Systems

17. Client Impact #2 • Problem – what happens in a partial network shutdown where the network (and therefore client) has reduced bandwidth. Does the client have any indication of such an environment? • Solution #1 – APs that remain active could continue to advertise that other parts of the network have shutdown, would inform the client that the network is in partial shutdown • Possible addition to proposal? Allan Thomson, Cisco Systems

18. Questions ? Allan Thomson, Cisco Systems

19. Straw Poll #1 • Do you think a normative text proposal on AP Power Notification should be considered for inclusion in TGv? • Yes: • No: • Don’t care: Allan Thomson, Cisco Systems

20. Straw Poll #2 • Which Solution do you prefer? (one vote only) • Solution #1: BSS Transition Management • Yes: • Solution #2: Neighbor Report • Yes: • Both Solution #1 and Solution #2 • Yes: • Other solution • Yes: Allan Thomson, Cisco Systems