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
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
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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
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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
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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
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