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**
Traditional Telephony
• Place call (Signaling)
• Directory lookup
• Circuit reservation
• Talk (Connectivity)
• Transfer voice data (analog, digital)
• Variations on these themes
• Multi-party conferencing
• Voicemail
2
IP-Based Communication Systems
Telephony
• Place call (Signaling)
• Directory lookup
• Packet switched routes
• Talk (Connectivity)
And More
• Video
• IM
• Status / buddy list
• Direct packet routing
• Media relaying
• PSTN/mobile gateways
3
Trends & Implications
• Trend away from traditional telephony infrastructure
• Vonage, Packet8, Verizon FiOS
• Skype
• Mobile
• 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?
4
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?
5
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
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
IP Communication Flavors
Client-Server (C/S)
Peer-to-Peer (P2P)
8
IP Communication Flavors
Traditional Telephony
Replacement
Communication
Addendum
9
How Does C/S IP-Telephony Work?
SIPSIP
registrar
/ /
registrar
proxy
/ presence
proxy
server
server
REGISTER
(1) signaling
(ip addr)
REGISTER
(1)
signaling
(ip addr)
IP-PSTN
gateway
PSTN / Mobile
(2) media
User agent
(voice, video, IM) User agent
Utopian Internet
No NATs or
firewalls
10
And In The Real-World…
SIP registrar /
proxy / presence /
server
media server
NAT / firewall
NAT / firewall
User agent
User agent
11
Media Servers Bypass Firewalls
SIP registrar /
proxy / presence /
server
media server
IP-PSTN
gateway
(1) signaling
NAT / firewall
PSTN / Mobile
(2) media
(1) signaling
NAT / firewall
(voice, video, IM)
(UDP or TCP)
User agents
User agents
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How Does P2P IP-Telephony Work?
media relay
(or relay)
node A
node E
NAT /
firewall
network address
media
of(3)
node
B? (TCP)
(2)
(4) media
(2) signaling
(1)
(3) signaling
PSTN / Mobile
P2P
P2P / PSTN
gateway
(1)
NAT /
firewall
node B
(1)
network address
(2)
of node E?
(1)
•
•
(2) signaling
node C
node = user agent
node D
•
nodes form an overlay
share responsibilities for
message routing, signaling,
media relaying
super nodes, ordinary nodes
13
Sources of Energy Consumption
• End-point
– Handsets
– VoIP conversion boxes
– PCs
• Core
– Signaling / directory
– Media relaying
– PSTN / mobile gateways
• Network
14
Assessing Energy Consumption
• Data (from C/S VoIP provider) • Power Meters
–
–
–
–
–
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
– 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
16
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!
17
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?
SIP registrar /
proxy / presence /
server
media server
media relay
(or relay) node A
NAT /
firewall
(3) media (TCP)
(2)
signaling
INVITE
media
node E
INVITE
NAT / firewall
(voice, video, IM)
(UDP or TCP)
User agents
P2P
(1)
NAT /
node B firewall
of node E?
(2) signaling
User agents
• C/S Inefficiencies
(1)
network address
node C
node D
– 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
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determinant of core energy consumption.
How Do Design Choices Effect Power
Consumption?
SIP registrar /
proxy / presence /
server
media server
media relay
(or relay) node A
NAT /
firewall
(3) media (TCP)
(2)
signaling
INVITE
media
node E
INVITE
NAT / firewall
(voice, video, IM)
(UDP or TCP)
User agents
• P2P Consumption
P2P
(1)
NAT /
node B firewall
(1)
network address
of node E?
(2) signaling
User agents
node C
node D
– 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?
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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
21
Modeling P2P and C/S
• C/S model
• P2P model
– C/S power consumption =
#servers * Watts/server *
redundancy factor * PUE
– S super nodes active
– ps super node consumption
P2P energy efficient when:
S * ps < C/S power consumption
• One active super node per
relayed call.
• Media server fully loaded.
• 100% calls relayed
ps = 52mW
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
23
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
24
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
25
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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