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Towards Eco-Friendly Home Networking

Mathias Gibbens, Chris Gniady and Beichuan ZhangDepartment of Computer Science

The University of ArizonaTucson, Arizona

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Home networks are complex

● More and more demand is being placed on router performance

● Routers require more computing power, bandwidth and features

NAS

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Complexity → Power

Power consumption doubled in 5 years, what about the future?

Always on in 88 million homes, energy footprint of $1 billion

g (2003) n (2009) ac (2013)

Power

CPU

RAM

Dual core!

WiFi Speed

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Previous solutions

● Wired: IEEE 802.3az introduced Energy-Efficient Ethernet

▪ First deployed in home networks

▪ Physical connection, easy to detect client

● Large mesh networks: many routers, many clients

▪ Power down redundant access points

▪ Client picks optimal network when more than one is available

● Home networks: one router, many clients

▪ Goma et al: aggregate individual networks

▪ Requires: dense networks, cooperation, client modifications

We need energy management for individual routers

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Our contribution

● Transparent energy optimization of personal networks

▪ Individual routers

▪ No user intervention or modification of clients

▪ No cooperation between networks

● Implementation approach

▪ Discarding unnecessary wireless traffic

▪ Powering down routers when idle

▪ Power cycling with active clients

● Increased energy efficiency of individual home routers

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Outline

Introduction

Trace collection and categorization

Proposed optimizations

Methodology

Results

Conclusion

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Traffic categorization

Traffic seen even without clients connected

Lots of idle time when clients are present

Router is in full power mode independent of clients

T1 T2 T3 T4 T50%

20%

40%

60%

80%

100%

No client broadcast No client Idle client Active client

Tim

e

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Eliminating broadcast traffic

Broadcast traffic, but no clients around to respond

Traffic from wired interface retransmitted over wireless

No one listening → drop broadcast traffic

Safe to perform: clients must be present in order to respond

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Client Broadcast

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Powering down when idle

No clients → power down antennas after a timeout

Periodically check for the arrival of new clients

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Client BroadcastLast client departs

Power down

Power up

Power

Look for clients

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Optimizing duty cycle: Downtime

● Duty cycle impacts a client's ability to connect

● Need to balance extra delay with potential energy savings

● Infrequent initial associations, which impact only first client

0 1 2 3 4 5 6 7 8 9 10 110

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20

30

Antenna down time [s]

Co

nne

ctio

n tim

e [

s]

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Optimizing duty cycle: Uptime

● Antennas must be up for at least 4 seconds for clients to connect

● From observed delays, we chose a 5/5 second up/down cycle

4 5 6 7 8 9 10 110

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Antenna up time [s]

Co

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ctio

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s]

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Idle connected clients

● During sufficiently long idle periods, turn off transmit antenna

● Possible because either clients initiate or data arrives on wire

● Router must still periodically announce its presence

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Client Broadcast

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Idle connected clients

● WiFi spectrum is inherently error prone

▪ Existing protocols have built in transparent retransmission to compensate

● Clients typically disconnect from network after 7 seconds

● Transparent retransmission gives us opportunity to power up

Time

ACK

No ACK, try resending Packet lost, inform user

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Idle connected clients

● Additional delay due to power up may be seen by applications

▪ Can be hidden in the time it takes for a response to return to the router

● Transitioning router's state has an energy cost

▪ Only sufficiently long periods should be optimized

▪ Ensures real time data is not interrupted

Router power

Client packet

Forward packet

Begin router power up

Complete

Response

Response to client

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Methodology

Monitor traffic seen at router: week long traces

Very few initial associations when no other clients present

Detailed power/delay model of ASUS RT-N16 profiled using NI

Trace T1 T2 T3 T4 T5

Average concurrent devices 1 5 4 4 2

Maximum concurrent devices 1 9 7 6 3

Initial associations 13 16 14 31 35

Average time with no client [h] 10.7 0.08 2.07 1.32 0.92

Traffic volume [GB] 5.57 40.21 4.22 3.52 12.97

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Eliminating broadcast traffic

No client period increased by 10% average in traces 2-5

More opportunities for router to power down

T1 T2 T3 T4 T50%

20%

40%

60%

80%

100%

No client broadcast No client Idle client Active client

Tim

e

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Power cycling no clients

Power cycling with no clients has significant impact

Additional connection delay for first client paid only occasionally

NB PC NB PC NB PC NB PC NB PCT1 T2 T3 T4 T5

0.0

0.1

0.2

0.3

0.4

0.5No client Idle client Active client

Ene

rgy

[MJ]

NB – No BroadcastPC - PowerCycle

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Active client optimizations

More aggressive power cycling can reduce energy consumption by an additional 20-30%

Cumulative energy savings observed to be 12-59%

PC

CT

CA

PC

CT

CA

PC

CT

CA

PC

CT

CA

PC

CT

CA

T1 T2 T3 T4 T5

0

0.1

0.2

0.3

0.4

0.5No client Idle client Active client

Ene

rgy

[MJ]

PC – PowerCycleCT – CycleTransmit

CA - CycleAll

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Delay due to state transition

Active clients see some delay when initiating activity after a period of idle time

All delays within perception threshold, not noticed by user

0 10 20 30 40 50 60 70 800%

20%

40%

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80%

100%T1 T2 T3 T4 T5

Additional delay [ms]

De

lays

se

en

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Conclusion

Investigated opportunities to reduce energy consumption of consumer wireless routers

Collected traces from personal networks

Predicted wireless energy consumption reduced by 12-59%

Changes do not break backwards compatibility

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Thank You

Questions?

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Trace collection and analysis

Five unique week-long traces collected from households

Routers recorded just the wireless traffic seen

Networks used as normal to produce representative traces

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Idle periods with clients

To save energy with clients, there must be many idle periods of sufficient length

Each trace has many long idle periods

24

816

3264

128256

5121024

>1024-20%

0%

20%

40%

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80%

100%T1 T2 T3 T4 T5

Idle time [s]

We

ight

ed

idle

tim

e