Greening the Switch

Greening the Switch

Ganesh Ananthanarayanan and Randy H. KatzUniversity of California, Berkeley

Presented ByRajesh Gadipuuri

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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 network switches

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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

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Outline

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

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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)

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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

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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)

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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 Loss8

Power Reduction Schemes

• Time Window Prediction- Adaptive Sleep Window- Wake-on-Packet

• Power Save Mode- Adaptive Sleep Window- Wake-on-Packet

• Lightweight Alternative

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Time Window Prediction [1]

Number of packets, N, in the window to

N > τ

Sleep for time ts

Process packets buffered during ts

No

Yes

LatencyIncrease

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-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

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

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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

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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

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Evaluation [1] – Time Window Prediction

1. Cluster Size vs. Power Savings 2. Cluster Size vs. Packet Loss

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Evaluation [2] – Time Window Prediction

• Power Savings:Shorter to produces higher savings

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Evaluation [3] – Time Window Prediction

• Packet Loss: For buffer sizes greater than 500 KB, packet loss is under 0.25% with WoP

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Power Reduction Schemes

• Time Window Prediction- Adaptive Sleep Window- Wake-on-Packet

• Power Save Mode- Adaptive Sleep Window- Wake-on-Packet

• Lightweight Alternative

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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

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Evaluation [1] – Power Save Mode

1. Cluster Size vs. Power Savings 2. Cluster Size vs. Packet Loss

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Evaluation [2] – Power Save Mode

• Power savings vs. Sleep time window• Power savings vs. Latency Bound

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Evaluation

• Power savings in PSM

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Power Reduction Schemes

• Time Window Prediction- Adaptive Sleep Window- Wake-on-Packet

• Power Save Mode- Adaptive Sleep Window- Wake-on-Packet

• Lightweight Alternative

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Lightweight Alternative

• Diurnal patterns in load w.r.t. time of day

• Networks are provisioned for peak-loads– Under-utilized during off periods

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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

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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.

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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

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Costs

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• 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)

Power SavingsPower Reduction Scheme Power Savings

TWP – Adaptive (t0 = 0.5s) 21.6%

TWP – WoP (t0 = 0.5s) 27.3%

PSM – Adaptive (t0 = 0.5s) 19.8%

PSM – WoP (t0 = 0.5s) 26.5%

LWA 30%

LWA combination with TWP 36%

LWA combination with PSM 34%

Optimal Power Reduction 33.9%

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

Conclusions

• Switch architecture – shadow port, wake-on-packet

• Power reduction schemes with bounded performance degradations

• Lightweight alternative is a power-cognizant network architecture

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Thank You!!!

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