«Insomnia in the Access»Or How to Curb Access Network Related Energy Consumption

Marco CaniniEPFL

Joint work with

Eduard Goma, Alberto Lopez Toledo, Nikolaos Laoutaris (Telefonica Research), Dejan Kostić (EPFL), Pablo Rodriguez (Telefonica Research) ,

Rade Stanojević (IMDEA Networks), Pablo Yagüe Valentín (Telefonica Research)

2

Greening the ICT

Datacenters Access network

?

BackbonePCs &

peripherals

3

Energy consumption of telcos

2.1 TWh

3.7 TWh

4.5 TWh

9.9 TWh

4

Access dominates energy consumption

20-30% 70-80% ACCESSBackbone/Metro/Transport

5

A typical DSL access network

CORE METRO

Gateway

USER PARTISP PARTACCESS

6

A typical DSL access network

CORE METRO

USER PARTISP PARTACCESS

DSL Access Multiplexers(DSLAMs)

Cable bundle

Central Office

Gateway

Distribution frames of a

Central Office7

Can we save energy?How?

1. Challenges in greening the access2. Two practical techniques can save of

the access energy …3. With a performance bonus

8

9

WHY DOES THE ACCESS CONSUME SO MUCH?

10

Individually, they do not consume a lot#1: Huge number of devices

PhotoBlackburn

But collectively …

2 orders of magnitude more gateways than DSLAMs

1 order of magnitude more DSLAMs than metro devices

2 orders of magnitude more DSLAMs than backbone devices

11

2#: High per bit energy consumption

At full load, access devices 2-3 orders of magnitude higher than metro/backbone

ACCESSBackbone/Metro

12

Energy proportionality?

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

Power Energy efficiency

Utilization [%]

Pow

er u

sage

[% o

f pea

k]

100%70%

13

3#: Utilization < 10%

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

Power Energy efficiency

Utilization [%]

Pow

er u

sage

[% o

f pea

k]

0 2 4 6 8 10 12 14 16 18 20 220%

2%

4%

6%

8%

10%

Daily utilization of 10K access links in a commercial ADSL provider

uplinkdownlink

Time [h]

Aver

age

utiliz

ation

[%]

… but most of the time hereAlready bad here

14

Sleeping saves energy

Sleep-on-Idle (SoI)Devices enter sleep mode upon periods of inactivity

15

METRO

SoI fails in access networks

USER PARTISP PARTACCESS

An ADSL line needs 1 minute to wake up… but cannot enjoy a minute’s sleep

16

What if we can put 80% of gateways to sleep?

15 W

100 W

1 W per modem

Save big fraction at the user side ISPs … not so much

17

Line cards very unlikely to sleep by SoI

Line cardsModem off

DSLA

M

Modem on

Static assignment of lines to DSLAM ports is a problem

⟹Greening the user part: aggregation

⟹Greening the ISP part: line switching

OUR APPROACH

18

19

Greening the user part – Aggregation

On average 5-6 WiFi networks overlap in typical urban settings

?

???

Broadband Hitch-Hiking (BH2)Threshold-based heuristic algorithm: direct traffic to

neighbor gateways during light traffic conditions

20

Broadband Hitch-Hiking(BH2)

5% 30%

20%

25%

0% 35%5%

30%50%45%

Load on home gateway is low direct light traffic to a neighbor gateway and let home gateway sleepLoad on neighbor gateway is low look for another neighbor or go back to home gatewayLoad on neighbor gateway is high go back to home gateway

15 W

21

BH2 under the hoodGateways assumed to have:• SoI• Ability to wake on traffic

BH2 terminals use WiFi card virtualization:[Giustiniano et al., MobiCom ’10; Kandula et al., NSDI ’08]

• Estimate load on all gateways in range• Maintain connectivity with 1 or few

backup gateways

Only modify the terminal wireless card driver

22

Greening the ISP part – Line switchingDS

LAM

Line cards

AT&T operators connecting transatlantic calls at the international switchboard in New York, circa 1930. (www.corp.att.com)

40-way switch

Full switching maximizes savings …but cost quickly grows with the number of ways

Switching is for lines, not for packets

23

Small 4-way switches are enough

Each k-switch packs active lines to the top

DSLA

M

Line cards

Put line cards to sleepSimple micro-electro-mechanical switches with near-zero power consumption

4-way switches

Evaluation

• Traces: CRAWDAD UCSD – 272 clients, 40 gateways• Scenario: 4 x 12-port line cards; 5.6 avg. gateways• Results for 4 schemes• Baseline: no sleep

– Gateways, modems, line cards don’t sleep– Each terminal only connects to its home gateway

24

25

How many gateways can sleep?

0 5 10 15 20 240

10

20

30

40

Time [h]Num

ber o

f sle

epin

g ga

tew

ays

SoI

Scheme 1: SoI for gateways, modems & line cards

Peak hours

26

How many gateways can sleep?

0 5 10 15 20 240

10

20

30

40

Time [h]Num

ber o

f sle

epin

g ga

tew

ays

SoI

BH2

BH2 puts to sleep 70-90% of gateways

Scheme 2: BH2 + k-switchBH2 every 150 s + 12 x 4-switches

27

How many gateways can sleep?

0 5 10 15 20 240

10

20

30

40

Time [h]Num

ber o

f sle

epin

g ga

tew

ays

SoI

BH2

Optimal

Scheme 3: OptimalBest clients to gateways assignment + full switch

28

What is the impact of gateway density?

1 2 3 4 5 6 7 8 9 100

5

10

15

20

25

30

35

40

Mean number of available gateways per clientNum

ber o

f sle

epin

g ga

tew

ays

Just home + 2 neighbors

50%+ of gateways sleep

29

How much energy can we save?

0 5 10 15 20 240

20

40

60

80

100

Time [h]Ene

rgy

savi

ngs

vs n

o-sl

eep

[%]

SoI

Optimal

BH2 + k-switch

BH2 + k-switch saves 66%Optimal savings are 80%

30

What are the savings for the ISP?

0 5 10 15 20 240

10

20

30

40

50

60

Time [h]

% o

f tot

al e

nerg

y sa

ving

son

the

ISP

sid

e

SoI + k-switch

SoI

Scheme 4: SoI + k-switchCombine switching with SoI

31

What are the savings for the ISP?

0 5 10 15 20 240

10

20

30

40

50

60

Time [h]

% o

f tot

al e

nerg

y sa

ving

son

the

ISP

sid

e

SoI + k-switch

SoI

BH2 + k-switch

Savings come from both aggregation and switching

32

What are the savings for the ISP?

0 5 10 15 20 240

10

20

30

40

50

60

Time [h]

% o

f tot

al e

nerg

y sa

ving

son

the

ISP

sid

e

Optimal SoI + k-switch

SoI

BH2 + k-switch

Savings come from both aggregation and switching

33

Prototypedeployment

2 4 6 8 10 12 14 16 18 20 22 24 26 28 300

2

4

6

8

Time [mins]Num

ber o

f sle

epin

g A

Ps

SoIBH2

1st floor 2nd floor 3rd floor

+

Limitation: home gateway + 2 neighbor gateways per client

34

Incentives

SecurityPrivacy

Considerations for deployment

35

A performance bonus

0 2 4 6 8 10 12 16 20

0

10

20

30

40

50

Number of inactive lines

Avg

. spe

edup

[%]

62 Mbps; loop lengths 50-600 m

Powering off lines makes the remaining … go faster due to reduced crosstalk!

Bonus: reduced crosstalk

Conclusions

• 80% energy can be saved at the access• Aggregation + switching save 66% of energy• Surprising result: turning DSL modems off increases

the performance of remaining modems

• Applying our solution to all DSL users worldwide, yields savings of 33 TWh per year– ½ of energy going into US datacenters Thank you!

Questions?

– Or the output of3 nuclear power plants

36