IEEE 802.21 MEDIA INDEPENDENT HANDOVER Title: Power Save Topics for Mobile Battery Powered Wireless Devices Date Submitted: July 15, 2008 Presented at IEEE 802.21 session #27 in Denver Authors or Source(s): Michael G. Williams, Padam Kafle (Nokia) Abstract: Discussion topics of power save at the network and lower layers. Discuss potential improvements through enhancements to MIH services. 21-08-0229-00-mrpm

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Power save related topics Outline Review of today’s system related power issues for mobile battery powered devices WLAN power save overview WCDMA power save overview Can .21 help ? 21-08-0229-00-mrpm

System related power drains Always-on applications and services are the current main cause of battery drain where 802.21 might help .21 cannot modify WCDMA or WLAN power save modes Applications require keep-alives from the terminal To refresh the application server To keep open the NATs or FWs in the network ‘Push’ apps and services require the terminal must be reachable Mobile email IM Voice, video (CoIP) VPN MIP 21-08-0229-00-mrpm

System related power drains Unified messaging / instant messaging services fring, gizmo, MSN, etc (not preinstalled in devices) large buddy groups and presence updates Peer-to-peer networks with variety of services increases traffic, power demands Location based applications Apps using low GPS fix rate Navigation use case is standard Music, Video services Streaming or download Youtube and other video services Watching and uploading Email to become an obvious item to haveh With push when needed or liked Browser Asynchronous Javascript (AJAX) et al Browser based apps utilize frequent messaging VPN usage intranet access, Internet through intranet Network and session layer mobility related traffic, keep-alives Understanding the power save features in use today can help to show the way for future improvements 21-08-0229-00-mrpm

NAT, FW, VPN, MIP Keep-alives Timers are used to close connections through these devices to help network devices conserve resources and improve security Commonly used in residential broadband connections, WLAN hotspot, 3G internet connections (almost everywhere for IPv4) Terminal can usually discover the presence of these, but still must send keep-alives within the timer interval to keep the session continuity The more mobility services that are running on the terminal, the more keep-alives are sent 21-08-0229-00-mrpm

Typical Cellular Internet Access Scenario RAN Internet NAT/FW GGSN, SAE GW, CSN GW Internet or corporate service Private addresses Public addresses In cellular/wireless network architectures (3GPP, 3GPP2, WMF) NAT/FW is typically located at the “access router”, i.e. the first IP level network element from the mobile host point of view Inbound traffic for a certain IP:port pair is allowed only after outbound traffic sent first. The state expires (for UDP ~30 seconds, TCP 5-60 min.) There is often only a single layer of NAT/FW If this NAT/FW bindings/pinholes could be explicitly controlled from the mobile host, excessive keep-alive traffic would not be needed 21-08-0229-00-mrpm

Multi Radio Power Consumption (relative measurements with SIP) Figures from 2006 implementations, for comparison only 21-08-0229-00-mrpm

NAT, FW, VPN, MIP Keep-alives UDP-based solutions used by e.g. VPNs and by most SIP services really power-consuming. TCP works better, but not a generic solution. Problem can’t be solved in devices/hosts alone, but it requires special support in the access networks (and in some cases servers) Perhaps MIH MRPM could help? New MIH SAP local services for coordination and control of keep-alive transmissions? Discover presence of timer values for NAT/FW/VPN/MIP via IS or ES? Configure timers to synchronize them, via CS or new service? Proxy keep-alive services up or downstream? 21-08-0229-00-mrpm

Power save related topics Outline Review of today’s system related power issues for mobile battery powered devices WLAN power save overview WCDMA power save overview Can .21 help ? 21-08-0229-00-mrpm

WLAN Power Save Overview WLAN supports power save mode (PSM) and Unscheduled Automatic Power Save Delivery (U-APSD) scheme, part of the WLAN QoS 802.11e/WMM work .11n will also support Power Save Multi Poll (PSMP) STA signals to AP it is going to from constant awake mode (CAM) to PSM STA goes to low power AP buffers downstream traffic, indicates the awaiting traffic via beacon Delivery Traffic Indicator Map (DTIM) STA wakes up periodically to check beacon DTIM from AP for traffic U-APSD STA wakes up anytime, PSM wakes up at scheduled time (typically awakes every 1-5 DTIMs) If DTIM indicates traffic, STA sends trigger frame to AP requesting delivery AP receives trigger frame and delivers data according to delivery mode in use 21-08-0229-00-mrpm

WLAN Power Save Overview A high-level state diagram of IEEE 802.11 power save Implementation of PSM and U-APSD is not consistent Some APs don’t buffer multicast or broadcast so these can be dropped (e.g. DHCP and ARP) Typically three behavioral modes in implementations: Never PS Sometimes PS on receive, never when transmit needed Always attempt to PS UI and applications aren’t coordinated. No standard MAC SAP services to indicate or control modes 21-08-0229-00-mrpm

WLAN Power Drain Causes Scanning contributes substantially to power drain Background scanning, even if no network, is common Hidden SSIDs take more power to scan due to probing Broadcast and Multicast traffic downstream can be large power drain for STAs NetBIOS, DHCP, UPnP control protocols of local bridges, switches, and access points AP encrypts and forwards traffic downstream, STA decrypts and drops unwanted traffic AP implementations often do proxy ARP, so hopefully no ARP traffic Small DTIM timer values Perhaps MIH MRPM could help? New MIH SAP local services for coordination and control? Proxy to handle unwanted traffic? Coordinated use of CS plus location to improve scanning intelligence? Use of ES over other radio to announce awaiting WLAN traffic ? 21-08-0229-00-mrpm

Power save related topics Outline Review of today’s system related power issues for mobile battery powered devices WLAN power save overview WCDMA power save overview Can .21 help ? 21-08-0229-00-mrpm

WCDMA Power Save Overview Overview of basic WCDMA radio resource control (RRC) state machine CELL_DCH (dedicated channel): Channel not shared, highest power use, giving maximum throughput and minimum delay CELL_FACH (forward access channel): Shared channel used when there is not much uplink traffic, about 50% power of CELL_DCH state. CELL_PCH (paging channel, optional): 1–2% of CELL_DCH power. If there are downlink packets for the terminal, the terminal will be paged. New states in newer releases (e.g. URA PCH) 21-08-0229-00-mrpm

WCDMA Power Save Overview Overview of basic WCDMA radio resource control (RRC) state machine Idle mode: No RRC connection, only paging can reach terminal Usually, the terminal will use the CELL_DCH state to send keep-alives keep-alives and push traffic (e.g. incoming e-mails) will consume a lot more power Some networks support the state transition from idle mode directly to CELL_FACH 21-08-0229-00-mrpm

WCDMA Power Save Overview Overview of basic WCDMA radio resource control (RRC) state machine Timers T1, T2 and T3 are controlled by radio network controller (RNC) to cause transition T1 is CELL_DCH state inactivity timer reset whenever there is traffic after expiring, terminal enters the CELL_FACH state. the shorter the T1 timer, the worse the user experience will be T1 value may depend on the DCH data rate Typical values used in RNC implementations are: 5 seconds for 8–32 kbit/s 3 seconds for 128 kbit/s 2 seconds for data rates greater than 128 kbit/s In some networks, significantly longer timers than these may be used 21-08-0229-00-mrpm

WCDMA Power Save Overview Overview of basic WCDMA radio resource control (RRC) state machine Timers T1, T2 and T3 are controlled by radio network controller (RNC) to cause transition T2 is CELL_FACH state inactivity timer If CELL PCH is used, terminal state machine will enter the CELL_PCH state after T2 expires If CELL_PCH is not used, the terminal state machine will enter the idle state Typical implementation value is 2 seconds but often significantly longer T2 values are used 21-08-0229-00-mrpm

WCDMA Power Save Overview Overview of basic WCDMA radio resource control (RRC) state machine Timers T1, T2 and T3 are controlled by radio network controller (RNC) to cause transition T3 is a timer used in CELL_PCH After staying in the CELL_PCH for T3 seconds, the RRC connection will be released Typical implementation value is long Minimum is several minutes Maximum can be tens of minutes 21-08-0229-00-mrpm

WCDMA Power Save Overview T1 and T2 define the time of device transitions from the more power-consuming states to less consuming states The sum T1+T2 defines the general power consumption behavior of the device T1 has a significant effect on the perceived performance of several applications T2 accounts for most of the idle battery performance in networks where CELL_PCH or idle-to-CELL_FACH transitions are available Short keep-alive packets can be transmitted in CELL_FACH state 21-08-0229-00-mrpm

WCDMA Power Save Overview In CELL_PCH state (or URA_PCH) terminal only responds to pages In CELL_PCH, terminal can use discontinuous reception (DRX) mode terminal powers off its receiver DRX mode is used when nothing else is needed to be done DRX cycle length is interval between two successive power ups cycle length affects battery performance Typical DRX cycle length is 1-2 seconds Increasing the DRX cycle length is a tradeoff: improves the stand-by battery performance increases the paging delays increases the packet roundtrip delays and call setup delays 21-08-0229-00-mrpm

WCDMA Power Save Overview 3GPP R7 and R8 allows major terminal power savings with Discontinuous transmission (DTX) and reception (DRX) Release 7 brings Continuous packet connectivity (CPC) which allows DTX and DRX for Cell_DCH state. L1 activity can be decreased by 70% for VoIP and by 85% of inactive terminal Release 8 brings DRX to FACH state. Lower power consumption for keep alive messages Web page download User reading web page User moved to FACH/PCH HS-DSCH HSPA R6 DPCCH Continuous packet connectivity HS-DSCH HSPA R7 DPCCH 21-08-0229-00-mrpm

WCDMA Power Save Overview Other aspects of mobility also drain power: Intersystem reselections Out-of-coverage conditions All of these states and intersystem mobility procedures are internal to 3G-2G radio systems, cannot be changed in 802.21 Perhaps MIH MRPM could help? MIH entities will likely not be in the PoA as they could be in IEEE based systems New MIH SAP local services for coordination and control? Coordinated use of CS plus location to improve scanning intelligence for multi radio terminals? Use of ES over other WCDMA radio to announce awaiting WLAN or WiMAX traffic ? 21-08-0229-00-mrpm

Power save related topics Outline Review of today’s system related power issues for mobile battery powered devices WLAN power save overview WCDMA power save overview Can .21 help ? 21-08-0229-00-mrpm

Summary of areas for MRPM work Develop new services and entities in following areas: (Refer to MRPM documents that describe new entities) New MIH SAP local services for coordination and control of power states New MIH SAP local services for coordination and control of keep-alive transmissions Coordinated use of CS plus location to improve scanning intelligence for multi radio terminals Use of ES over active radio to announce awaiting WLAN or WiMAX traffic Discover presence of timer values for NAT/FW/VPN/MIP via IS or ES Configure timers to synchronize them, via CS or new service Proxy keep-alive services up or downstream in new PoA entity Proxy to handle unwanted traffic in new PoA entity 21-08-0229-00-mrpm