Greening the Switch

1. Greening the Switch Ganesh Ananthanarayanan and Randy H. Katz University of California, Berkeley Presented By Rajesh Gadipuuri

2. Motivation • Power consumption of Internet equipment is enormous (~$24 billion per year) • Includes switches, end-hosts, servers • Efforts to design energy-efficient network equipment • Energy Efficient Ethernet (EEE), Energy Star • Reduce power consumption of networkswitches

3. Problems and Goals • Network traffic is observed to be… • Bursty with interspersed idle periods • Diurnal variations • Heavily underutilized network equipment • Theme: Performance vs. power savings • The proposed schemes are stand-alone and hence incrementally deployable

4. Outline • Switch Architecture • Power Model • Port Design • Wake-on-Packet • Buffering • Shadow Ports • Time Window Prediction • Power Save Mode • Lightweight Alternative • Conclusions

5. Switch Architecture – Power Model • Switch power consumption - Chassis (Powerfixed) - Switching fabric (Powerfabric) - Line card (Powerline-card) - Ports (Powerport) Powerswitch = Powerfixed + Powerfabric + numLine * Powerline-card + numPort * Powerport • Schemes concentrate on putting only ports to sleep • Total power consumption of ports is 39.4% (Cisco Power Calculator, with four line-cards each containing 192 ports)

6. Port Design [1] • Two state power model • High and low power • Transition takes finite time and power • Wake-on-Packet • Avoids the overhead of timer-driven transitions to high-powered state during sustained idle periods • Automatically wake up when a packet arrives

7. Port Design [2] – Buffering • Packets need to be buffered when a port is powered down • Processes the buffered packets when a port transitions back to high powered state • Inbound packets are lost if the port’s circuitry is down (Current design)

8. Port Design [3] – Shadow Ports • Receives ingress packets if atleast two of the mapped normal ports are powered down • Similar hardware as normal ports • At least two normal ports need to be powered down simultaneously for power savings • Receives only one packet at a time • Simultaneous arrival  Packet Loss

9. Power Reduction Schemes • Time Window Prediction • Adaptive Sleep Window • Wake-on-Packet • Power Save Mode • Adaptive Sleep Window • Wake-on-Packet • Lightweight Alternative

10. Time Window Prediction [1] • Egress packets that arrive at a port when it is asleep are buffered and sent after the port wakes up • Ingress packets are handled by shadow port and incur no latency Number of packets, N, in the window to Latency Increase Yes Process packets buffered during ts N > τ No Sleep for time ts

11. Time Window Prediction [2] • Adaptive Sleep Window: - TWP is supplied with per-port bound on the tolerable increase in per packet latency - Adapt the sleep time-window (ts) to meet the latency bound • Lower bound for sleeping it set to twice the transition time

12. Time Window Prediction [3] • Wake-on-Packet: • Ports periodically wake up at the end of sleep window • During sustained idle periods, the energy expended due to periodically waking up and staying awake for units to before powering down is significant wasted • If there are no packets in multiple to windows, sleep continuously until a packet arrives

13. Evaluation – Traces • Traces collected from an enterprise network • Power reduction schemes produce power savings upto 20 to 35% • With the appropriate hardware support in the form WoP, Shadow ports and fast transitioning of the ports between the high and low power states, these power savings reach 90% of optimal algorithm

14. Evaluation [1] – Time Window Prediction 1. Cluster Size vs. Power Savings 2. Cluster Size vs. Packet Loss

15. Evaluation [2] – Time Window Prediction • Power Savings: Shorter to produces higher savings

16. Evaluation [3] – Time Window Prediction • Packet Loss: For buffer sizes greater than 500 KB, packet loss is under 0.25% with WoP

17. Power Reduction Schemes • Time Window Prediction • Adaptive Sleep Window • Wake-on-Packet • Power Save Mode • Adaptive Sleep Window • Wake-on-Packet • Lightweight Alternative

18. Power Save Mode[1] • Similar to wireless networks • Power Save Mode is primarily based on the switch’s capability to buffer packets • The sleep in PSM happens with regularity and is not dependant on the traffic flow • Aggressive and periodic sleep, but adaptive • Implements Adaptive sleep Window and WoP similar to TWP

19. Evaluation [1] – Power Save Mode 1. Cluster Size vs. Power Savings 2. Cluster Size vs. Packet Loss

20. Evaluation [2] – Power Save Mode • Power savings vs. Sleep time window • Power savings vs. Latency Bound

21. Evaluation • Power savings in PSM

22. Power Reduction Schemes • Time Window Prediction • Adaptive Sleep Window • Wake-on-Packet • Power Save Mode • Adaptive Sleep Window • Wake-on-Packet • Lightweight Alternative

23. Lightweight Alternative • Diurnal patterns in load w.r.t. time of day • Networks are provisioned for peak-loads • Under-utilized during off periods

24. Lightweight Alternative – Solution • Time Window Prediction and Power Save mode algorithms – ports • Macroscopic view of the traffic as well as switch • Lightweight alternative switch for every high-powered switch • Identify slots of low activity • Only one of the two is powered up • All machines have connectivity through the high powered switch as well as lightweight alternative • The system uses the simple k-Means clustering algorithm to identify slots of low activity

25. Lightweight Alternative – Design Alternatives • Lightweight Switch: • Each line card can be substituted by a separate lightweight switch • Integrated switches can be used as lightweight alternatives • Routing tables and other configuration information for the lightweight switch can be transferred from the main switch using protocols like GARP, VLAN registration protocol (GVRP) • Wireless: • Connectivity through wireless access point.

26. Combining TWP and PSM with Lightweight Alternative • One of the high-powered switch or the lightweight alternative is powered up depending on the prediction for the slot • Switches employ either TWP or PSM • Assume WoP, port-transition time of 10ms, latency bound of 10ms for TWP and PSM • Power savings from Lightweight Alternative together with the TWP and PSM is higher than individual savings

27. Costs • Lightweight Alternative scheme proposes adding extra hardware in the network • Average power savings per day is 30% which translates to an economic savings of $37,133 in one year • Economic benefits obtained by power savings are clearly higher than the price of the extra hardware (Lightweight Alternative)

28. Power Savings Themes are evaluated using traces from a Fortune 500 company’s enterprise network of PC clients and file and other servers

29. Conclusions • Switch architecture – shadow port, wake-on-packet • Power reduction schemes with bounded performance degradations • Lightweight alternative is a power-cognizant network architecture

30. Thank You!!!