How Green is IP-Telephony?

Salman Abdul Baset*, Joshua Reich*, Jan Janak**, Pavel Kasparek**, Vishal Misra*, Dan Rubenstein*, Henning Schulzrinne*

Department of Computer Science, Columbia University*

Tekelec Corporation**

2

Traditional Telephony

• Place call (Signaling)• Directory lookup• Circuit reservation

• Talk (Connectivity)• Transfer voice data (analog, digital)

• Variations on these themes• Multi-party conferencing• Voicemail

3

IP-Based Communication Systems

• Place call (Signaling)• Directory lookup• Packet switched routes

• Talk (Connectivity)• Direct packet routing• Media relaying• PSTN/mobile gateways

Telephony And More• Video• IM• Status / buddy list

• Trend away from traditional telephony infrastructure• Vonage, Packet8, Verizon FiOS• Skype• Mobile

4

Trends & Implications

• To single infrastructure (IP) for all data/voice/etc.• More efficient (one system to maintain, improve)• Much less expensive (for now)• More fragile (one system to fail)• More complex

So what does this mean energy wise?

5

Our Questions

1) Where is energy consumed?

2) How do different design choices effect energy consumption?

3) How we can make IP-telephony more energy efficient?

6

Outline

• IP-Telephony and power consumption

• Answering our questions:1) Where is energy consumed?

2) How do different design choices effect energy consumption?

3) How we can make IP-telephony more energy efficient?

• Conclusion & Future Work

7

Outline

• IP-Telephony and power consumption

• Answering our questions:1) Where is energy consumed?

2) How do different design choices effect energy consumption?

3) How we can make IP-telephony more energy efficient?

• Conclusion & Future Work

8

IP Communication Flavors

Client-Server (C/S) Peer-to-Peer (P2P)

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IP Communication Flavors

Traditional TelephonyReplacement

CommunicationAddendum

10

How Does C/S IP-Telephony Work?SIP registrar / proxy server

REGISTER(ip addr)

REGISTER(ip addr)

User agent User agent

(1) signaling (1) signaling

(2) media(voice, video, IM)

SIP registrar / proxy / presenceserver

Utopian Internet

No NATs or firewalls

PSTN / Mobile

IP-PSTN gateway

11

And In The Real-World…SIP registrar / proxy / presence / server

User agent User agent

media server

NAT / firewall

NAT / firewall

12

Media Servers Bypass Firewalls

PSTN / Mobile

SIP registrar / proxy / presence / server

User agents User agents

(1) signaling

(1) signaling(2) media

(voice, video, IM)(UDP or TCP)

media server

NAT / firewall

NAT / firewall

IP-PSTN gateway

13

How Does P2P IP-Telephony Work?

P2P / PSTN gateway

PSTN / Mobile

NAT / firewall

NAT / firewall

network address of node B?

(3) signaling

(4) media

network addressof node E?

(2) signaling

(2) signaling(3) media (TCP)

node C

node B

media relay (or relay)

P2P

node A

node D

node E

(1)

(2)

node = user agent

• nodes form an overlay

• share responsibilities for message routing, signaling, media relaying

• super nodes, ordinary nodes

(1)(2)

(1)(1)

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Sources of Energy Consumption• End-point

– Handsets– VoIP conversion boxes– PCs

• Core– Signaling / directory – Media relaying– PSTN / mobile gateways

• Network

15

Assessing Energy Consumption

• Data (from C/S VoIP provider) – 100 K users (mostly business)– 15 calls per second (CPS) – ~5K calls in system – NAT keep-alive traffic – All calls relayed

• Modeling– C/S– P2P

• Power Meters

– Wattsup– Killawatt

• Hardware Measurements– SIP Server– Relay Server – Desktop clients– Laptop clients– Hardware SIP phones– Software phones– Skype peers

16

Outline

• IP-Telephony and power consumption

• Answering our questions:1) Where is energy consumed?

2) How do different design choices effect energy consumption?

3) How we can make IP-telephony more energy efficient?

• Conclusion & Future Work

17

Where is Energy Consumed?

PSTN replacement

• VoIP servers consume less than 0.04% of total!– >10K users, voice traffic– a server can handle signaling workload for 500k users – a server can handle media workload for 50k users– even after a redundancy factor of 2, and conservative

PUE of 2!

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Where is Energy Consumed?

Non-PSTN replacement

• More complicated• If softphone draws little additional power

– Still likely that end-point biggest component– But may not dominate consumption

• If users leave PCs on just as phones– Possibly even worse than PSTN!

User / hardware study needed.

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How Do Design Choices Effect Power Consumption?

• C/S Inefficiencies– Power utilization efficiency – (PUE)

• Ratio of data center power draw to IT power draw• e.g., cooling, network equipment, etc.

– Idle power consumption (can be addressed in larger systems by techniques such as Somniloquy or Sleep Proxy

– Percentage of user population that requires relaying major determinant of core energy consumption.

SIP registrar / proxy / presence / server

User agents User agents

INVITE

INVITEmedia(voice, video, IM)

(UDP or TCP)

media server

NAT / firewall

NAT / firewall

NAT / firewall

network addressof node E?

(2) signaling

(2) signaling

(3) media (TCP)

node C

node B

media relay (or relay)

P2P

node A

node D

node E

(1)(1)

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How Do Design Choices Effect Power Consumption?

• P2P Consumption– Avoids these overheads by using machines that are already on

• In theory general user population• In practice appears to be heavily subsidized by university machines• What happens when machines are idling less…

– Incurs small additional energy use for signaling and relaying• But how small?

SIP registrar / proxy / presence / server

User agents User agents

INVITE

INVITEmedia(voice, video, IM)

(UDP or TCP)

media server

NAT / firewall

NAT / firewall

NAT / firewall

network addressof node E?

(2) signaling

(2) signaling

(3) media (TCP)

node C

node B

media relay (or relay)

P2P

node A

node D

node E

(1)(1)

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Comparing C/S and P2P• Compare under same load

– Active calls– Call duration– Percentage of PSTN calls

• Generic C/S and P2P– Both use standard VoIP (e.g., not Skype)

• Isolate only services that differ between P2P, CS– Directory service – Call signaling – Media session – Presence

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Modeling P2P and C/S• C/S model

– C/S power consumption = #servers * Watts/server *redundancy factor * PUE

• P2P model– S super nodes active– ps super node consumption

ps = 52mW

P2P energy efficient when:

S * ps < C/S power consumption

• One active super node per relayed call.

• Media server fully loaded.• 100% calls relayed

P2P may consume more than C/S!

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Caveats• Peers

– External meters do not provide sufficient resolution to determine ps w/ confidence

– Will be in different states when relay starts• Medium load unlikely to incur much extra overhead

• Low or high loads, ps could conceivably be large

• Consequently, prior distribution effects efficiency

• Servers– Energy usage not linear w/ load– Lower utilization hurts energy efficiency

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Making IP-Telephony Greener

• Make phones energy efficient– LCD, processor, WOL for phones?

• NATs & Firewalls– Get rid of NATs or rearchitect them– Use TCP to avoid NAT keep-alive– Make firewalls VoIP-friendly.

• Set up SIP user agents on gateways

• PC wakeup on receiving calls

25

Outline

• IP-Telephony and power consumption

• Answering our questions:1) Where is energy consumed?

2) How do different design choices effect energy consumption?

3) How we can make IP-telephony more energy efficient?

• Conclusion & Future Work

26

Conclusions

• VoIP endpoints dominate total energy consumption in PSTN replacement systems

• P2P not necessarily more energy efficient than C/S.

• NATs and firewalls create the need for media relaying, one of the biggest components of core energy consumption.

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Future Work

• Obtain data on PSTN power consumption

• Work on accurately measuring ps

• Measure path length / routing differences between of direct and media-relayed calls.

• Study user behavior viz-a-vis softphone use

– How much extra time are machines left on

– Power draw during those periods

• Develop WOL capable hard-phones