1. Worcester Polytechnic Institute 1 Exploiting Idle Communication Power to Improve Network Performance and Energy Efficiency Lei Guo, Xiaoning Ding, Haining Wang, Qun Li, Songqing Chen, Xiaodong Zhang Proceedings of the 25th IEEE Annual Conference on Computer Communications (IEEE INFOCOM 2006), Barcelona, Spain, April 23-29, 2006. Presented by Michael Putnam (Some images and slides taken from INFOCOM presentation - http://www.cse.ohio-state.edu/~lguo/ )

2. Worcester Polytechnic Institute 2 Author Bio’s Ohio State University –Lei Guo Ph.D. candidate in CSE Member of High Performance Computing and Software Lab Researches: Internet measurements and modeling Streaming media delivery over the Internet Wireless systems and networking –Xiaoning Ding Ph.D. candidate in CSE Researches: Operating Systems Computer architecture Wireless systems and networking –Xiaodong Zhang Chairman of the Department of CSE Researches: Fast Data Accesses Resource Sharing OUTLINE BIOGRAPHIES Introduction Related Work Motivation System Models Channel Allocation System Design Experiments Conclusion

3. Worcester Polytechnic Institute 3 Author Bio’s College of William and Mary –Haining Wang Assistant Professor Department of CS Researches: Network QoS Internet architecture Wireless and sensor networks –Qun Li Assistant Professor Department of CS Researches: Wireless and Sensor Networks Embedded Systems OUTLINE BIOGRAPHIES Introduction Related Work Motivation System Models Channel Allocation System Design Experiments Conclusion

4. Worcester Polytechnic Institute 4 Author Bio’s George Mason University –Songqing Chen Assistant Professor Department of CS Researches: Distributed Systems High Performance Computing P2P Systems Internet Systems OUTLINE BIOGRAPHIES Introduction Related Work Motivation System Models Channel Allocation System Design Experiments Conclusion

5. Worcester Polytechnic Institute 5 Challenges in Wireless System Design Energy saving is not easy –Limited battery capacity in wireless devices –High power consumption in wireless communication High performance costs energy and fairness –Wireless users demand high throughput, but … – A high throughput device needs less sleep. – A channel allocation mechanism can favor some but degrade performance of others. Can we win both instead of addressing the trade-off? OUTLINE Biographies INTRODUCTION Related Work Motivation System Models Channel Allocation System Design Experiments Conclusion

6. Worcester Polytechnic Institute 6 Energy consumption A simple way to save energy –Put the WNI into sleep mode when idle (for a 5 V device) > 50% total energy up to 10% total energy high power mode 450 mA low power mode 15 mA Power Consumption for Mobile Devices OUTLINE Biographies INTRODUCTION Related Work Motivation System Models Channel Allocation System Design Experiments Conclusion

7. Worcester Polytechnic Institute 7 802.11 Power Saving Mechanism Access point –Buffer data for sleeping stations –Broadcast beacon with TIM periodically (100 ms) Sleeping station –Wake up periodically to receive beacon –Poll access point to receive data –Sleep again Access Point Internet Traffic Indication Map (TIM) sleeping station wake up poll receive data OUTLINE Biographies Introduction RELATED WORK Motivation System Models Channel Allocation System Design Experiments Conclusion

8. Worcester Polytechnic Institute 8 Observations of IEEE 802.11 Protocol A client/server model –Each station independently communicates with AP –AP serves a station one at a time via the channel. The saving mode affects TCP traffic –Increasing RTT and decreasing throughput. Performance anomaly (Infocom’03) –Non-uniform transfer rates between different stations to AP due to distance and obstacle condition differences. –A low speed station has low channel utilization rate. Waste energy while a station is waiting for its turn. –Idle communication power due to strong dependency OUTLINE Biographies Introduction RELATED WORK Motivation System Models Channel Allocation System Design Experiments Conclusion

9. Worcester Polytechnic Institute 9 Performance Anomaly in WLAN Multiple channel rates in PHY –Larger coverage –Varying channel conditions Same MAC control for all channel rates –Same opportunity to get channel –Different channel holding time for sending frame Performance anomaly (INFOCOM’03) –All stations have the same flow rate –Unfair to high channel rate stations –Low channel utilization OUTLINE Biographies Introduction RELATED WORK Motivation System Models Channel Allocation System Design Experiments Conclusion

10. Worcester Polytechnic Institute 10 Existing Solutions to address the Limits Reducing idle communication power by –Traffic prediction: bounded slowdown (MOBICOM’02) –Self-tuning with application hints (MOBICOM’03) –Limits: case by case, and accuracy can vary. Address the performance anomaly –Time-based fairness scheduling: a constant time unit is given to each device (USENIX 04) –Limits: poorly conditioned devices suffer: fast is faster, and slow is slower. Purpose of this paper: to win both performance and energy OUTLINE Biographies Introduction RELATED WORK Motivation System Models Channel Allocation System Design Experiments Conclusion

11. Worcester Polytechnic Institute 11 Source of Idle Communication Power While the channel is used by one station, idle communication power is wasted in many other stations AP Wireless performance anomaly makes this power waste worse, but also with an opportunity. OUTLINE Biographies Introduction Related Work MOTIVATION System Models Channel Allocation System Design Experiments Conclusion

12. Worcester Polytechnic Institute 12 Multi-hop Relay To help low channel rate stations to Increase throughput and extend network coverage AP X OUTLINE Biographies Introduction Related Work MOTIVATION System Models Channel Allocation System Design Experiments Conclusion

13. Worcester Polytechnic Institute 13 Multi-hop Relays Leverage Strong Dependency Slow stations become faster –Completing the data transfer ahead of the unit time. –Equivalent to move the station closer to AP or improve the station’s communication condition. Faster stations serve as proxies for slow stations –Performance improvement of slow stations reduced the waste of idle communication powers of fast stations --- shortening the waiting time. Effective P2P coordination among stations is the key. OUTLINE Biographies Introduction Related Work MOTIVATION System Models Channel Allocation System Design Experiments Conclusion

14. Worcester Polytechnic Institute 14 Incentive and Fairness to Fast Stations Why not sleep or wait, but proxy/relay for others? –Sleep lowers throughput, and wait wastes energy. –Idle communication energy can be used –The saved time in slow stations should be contributed. How much service is fair in a shared radio channel? –A proxy should be paid for its service –For either proxy or client, the throughput and energy utilization should be improved. OUTLINE Biographies Introduction Related Work MOTIVATION System Models Channel Allocation System Design Experiments Conclusion

15. Worcester Polytechnic Institute 15 Rationale Energy efficiency: what does a user care about? –Energy per second –Energy per bit: time is energy Self-incentive multi-hop relay with TBF –Use channel time to pay the relay service A win-win solution ThroughputEnergy efficiency ProxyIncreaseNo loss ClientIncrease OUTLINE Biographies Introduction Related Work MOTIVATION System Models Channel Allocation System Design Experiments Conclusion

16. Worcester Polytechnic Institute 16 System Model Time based fairness in shared radio channel Principle of proxy forwarding –Proxy: throughput  idle time  energy/bit  –Client: channel rate  throughput  S1S1 S2S2 …SiSi …SnSn t i =  t = 1/n 1 round idle SqSq Client SpSp Proxy S0S0 AP OUTLINE Biographies Introduction Related Work Motivation SYSTEM MODELS Channel Allocation System Design Experiments Conclusion

17. Worcester Polytechnic Institute 17 Analytic Definitions Power Consumption – P(S i ) –Joules / sec Throughput – T(S i ) –The number or effective bits a station transmits per unit time (not including retransmissions, or forwarding data for other stations) Energy Utility – E(S i ) –Average number of effective bits per unit energy OUTLINE Biographies Introduction Related Work Motivation SYSTEM MODELS Channel Allocation System Design Experiments Conclusion

18. Worcester Polytechnic Institute 18 Analytic Definitions Throughput Gain Energy Gain OUTLINE Biographies Introduction Related Work Motivation SYSTEM MODELS Channel Allocation System Design Experiments Conclusion

19. Worcester Polytechnic Institute 19 Channel Time Allocation (single-hop) OUTLINE Biographies Introduction Related Work Motivation System Models CHANNEL ALLOCATION System Design Experiments Conclusion

20. Worcester Polytechnic Institute 20 Lemma 1 (single-hop) Time utilization of a client S q when it pays the cost price to its proxy S p for the forwarding service is OUTLINE Biographies Introduction Related Work Motivation System Models CHANNEL ALLOCATION System Design Experiments Conclusion

21. Worcester Polytechnic Institute 21 Lemma 1 (single-hop) Rewarding time of a client S q when it pays the cost price to its proxy S p for the forwarding service are Amount needed to keep energy utility of proxy unchanged Cost for the proxy to listen to the client and talk to the AP OUTLINE Biographies Introduction Related Work Motivation System Models CHANNEL ALLOCATION System Design Experiments Conclusion

22. Worcester Polytechnic Institute 22 Lemma 1 (single-hop) Throughput gain of a client S q when it pays the cost price to its proxy S p for the forwarding service are Energy Utility gain of a client S q when it pays the cost price to its proxy S p for the forwarding service is OUTLINE Biographies Introduction Related Work Motivation System Models CHANNEL ALLOCATION System Design Experiments Conclusion

23. Worcester Polytechnic Institute 23 Lemma 1 (single-hop) Relaying is only useful when the Throughput Gain Since U(S q ) < 1, Note that Which Implies Relaying can increase the Energy Utility of a client station as long as its Throughput can be improved OUTLINE Biographies Introduction Related Work Motivation System Models CHANNEL ALLOCATION System Design Experiments Conclusion

24. Worcester Polytechnic Institute 24 Lemma 2 (single-hop) Assume station S p provides forwarding services to k client stations, S q1, S q2,..., S qk (k > 1), and these client stations independently contribute their rewarding time to S p to keep the energy utility of S p unchanged, we have U(S p ) = 1 and = 1: “…easy to see…” – authors OUTLINE Biographies Introduction Related Work Motivation System Models CHANNEL ALLOCATION System Design Experiments Conclusion

25. Worcester Polytechnic Institute 25 Lemma 2 (single-hop) Throughput Gain –The effective time of S p is Thus, OUTLINE Biographies Introduction Related Work Motivation System Models CHANNEL ALLOCATION System Design Experiments Conclusion

26. Worcester Polytechnic Institute 26 Channel Time Allocation (multi-hop) S0S0 S1S1 S i-1 SiSi OUTLINE Biographies Introduction Related Work Motivation System Models CHANNEL ALLOCATION System Design Experiments Conclusion

27. Worcester Polytechnic Institute 27 Lemma 3 (multi-hop) Assume each station has at most one immediate relaying station in a WLAN, and each station rewards its relaying stations independently to keep their energy utilities unchanged. For station S i that is relayed by i – 1 (i ≥ 1) stations along the path S 0 → S 1 →... → S i – 1 → S i, and S i has m i indirect or direct clients (S q1, S q2,..., S qmi ), we have Where and OUTLINE Biographies Introduction Related Work Motivation System Models CHANNEL ALLOCATION System Design Experiments Conclusion

28. Worcester Polytechnic Institute 28 Selfish Forwarding - SFW Proxy discovery and selection –A poorly conditioned client broadcasts a request to relay his packets –AP assigns a relaying station for clients based on the game theory (second price auction) to provide fairness for competition among proxy candidates HELP! OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation SYSTEM DESIGN Experiments Conclusion AP

29. Worcester Polytechnic Institute 29 Selfish Forwarding - SFW Proxy discovery and selection –AP collects the bids within a bidding time window –AP selects winner based on “second price sealed bid” rule (highest bidder wins, but only pays second highest price) –Client sends a request to the proxy –Proxy ACKs, and notifies the AP of the association HELP! OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation SYSTEM DESIGN Experiments Conclusion

30. Worcester Polytechnic Institute 30 Selfish Forwarding - SFW Channel allocation and scheduling –Easy to do under PCF - but since most commercial products only support DCF, there is a need for a scheduling algorithm – AP distributes tokens for fairness without any enforcement. –The relaying actions are determined by token exchanges among stations. OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation SYSTEM DESIGN Experiments Conclusion

31. Worcester Polytechnic Institute 31 Basic Idea of Token-based Channel Scheduling A token is a ticket for a data transfer (RX/TX) in one time unit AP initially distributes an equal amount of tokens to each station (fairness). A pair of RX & TX consumes one token. Token bucket model to fully use transmission channel. Multi-hop forwarding to increase throughput Incentive rewards to proxies OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation SYSTEM DESIGN Experiments Conclusion

32. Worcester Polytechnic Institute 32 Token and Token Bucket Model packets tokens from AP Overflow! Re-allocate to other stations by AP Token Bucket Packet Queue Transmitter 1 token per packet OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation SYSTEM DESIGN Experiments Conclusion

33. Worcester Polytechnic Institute 33 Multi-hop Forwarding AP S1S1 STAProxyRate S1S1 ---R(0,1) S2S2 ---R(0,2) S3S3 S2S2 R(0,3) S4S4 S2S2 R(0,4) S2S2 S3S3 S4S4 HopStationRate 1SelfR(0,2) 2S3S3 R(2,3) S4S4 R(2,4) HopStationRate 1S2S2 R(0,2) 2SelfR(2,3) OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation SYSTEM DESIGN Experiments Conclusion

34. Worcester Polytechnic Institute 34 Multi-hop Forwarding AP S1S1 R(0,4)S2S2 S4S4 R(0,3)S2S2 S3S3 R(0,2)---S2S2 R(0,1)---S1S1 RateProxySTA S2S2 S3S3 S4S4 R(2,3)S3S3 R(2,4)S4S4 2 R(0,2)Self1 RateStationHop R(2,3)Self2 R(0,2)S2S2 1 RateStationHop Each frame has Src / Dest MAC address Upon receipt of frame, node looks up Dest in table to see who to send to next Puts that addy in the Dest field and forwards the frame Then updates its channel rate field for the link received on to compute cost price of forwarding service. OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation SYSTEM DESIGN Experiments Conclusion

35. Worcester Polytechnic Institute 35 Multi-hop Path Maintenance Channel rates vary due to mobility or changes in the environment conditions – possible broken paths Each client periodically re-evaluates the forwarding service If the service quality is degraded, looks for a new proxy ( What threshold determines significantly degraded service? ) OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation SYSTEM DESIGN Experiments Conclusion

36. Worcester Polytechnic Institute 36 Multi-hop Power Management Power saving mode (no clients) –notify the AP directly Power saving mode (with clients) –Notify immediate children –Children recursively notify their children –After receiving all ACK’s – notify the AP –Clients look for new proxies OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation SYSTEM DESIGN Experiments Conclusion

37. Worcester Polytechnic Institute 37 Implementation and Experiments AP –NetGear MA311 802.11b PCI wireless adaptor –Linux kernel 2.4.20 –HostAP linux driver v0.1.3 Wireless Stations (6) –NetGear MA401 802.11b PCMCIA wireless adaptor –ORiNOCO Linux driver v0.15rc2 Traffic –FTP (presented in the paper) –Web (results in tech report) OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation System Design EXPERIMENTS Conclusion

38. Worcester Polytechnic Institute 38 Implementation Bidding time – 50 ms Token distribution interval – 100 ms Token value – 20 µs channel time Host AP distributes tokens evenly based on number of stations, then transfers rewarding tokens from clients to proxies OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation System Design EXPERIMENTS Conclusion

39. Worcester Polytechnic Institute 39 Protocols Compared DCF –Most widely used protocol in 802.11b network –Distributed Coordination Function TBF –Time-based Fairness (proposed USENIX 2004) SFW –Selfish Forwarding (authors’ homebrew) OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation System Design EXPERIMENTS Conclusion

40. Worcester Polytechnic Institute 40 Single Client Experiment AP 11Mbps 1Mbps Large file download from AP to proxy / clients Throughput measured at each hop Energy consumption computed (not measured) –Tx time * power consumption (as provided by the manufacturer) OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation System Design EXPERIMENTS Conclusion

41. Worcester Polytechnic Institute 41 Performance Evaluation Channel allocation scheme 1 proxy (P), 1 client (Q) OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation System Design EXPERIMENTS Conclusion

42. Worcester Polytechnic Institute 42 Multi-clients Experiment AP 11Mbps 1Mbps OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation System Design EXPERIMENTS Conclusion

43. Worcester Polytechnic Institute 43 Performance Evaluation 1 proxy (P), 5 clients (Q) OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation System Design EXPERIMENTS Conclusion

44. Worcester Polytechnic Institute 44 Performance Evaluation Proxy throughput gain 1 proxy, multiple clients OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation System Design EXPERIMENTS Conclusion

45. Worcester Polytechnic Institute 45 Conclusion Address throughput degradation caused by low-rate stations (Performance Anomaly ’03) Utilize energy waste in idle channel listening High Channel-rate station forwards data for low-rate station Clients reward proxy with additional channel time Everyone’s throughput can increase without suffering energy efficiency OUTLINE Biographies Introduction Related Work Motivation System Models Channel Allocation System Design Experiments CONCLUSION

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