How Green is IP-Telephony?

1. 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 Telephony And More • Place call (Signaling) • Directory lookup • Packet switched routes • Talk (Connectivity) • Direct packet routing • Media relaying • PSTN/mobile gateways • Video • IM • Status / buddy list

4. 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?

5. Our Questions • Where is energy consumed? • How do different design choices effect energy consumption? • How we can make IP-telephony more energy efficient?

6. Outline • IP-Telephony and power consumption • Answering our questions: • Where is energy consumed? • How do different design choices effect energy consumption? • How we can make IP-telephony more energy efficient? • Conclusion & Future Work

7. Outline • IP-Telephony and power consumption • Answering our questions: • Where is energy consumed? • How do different design choices effect energy consumption? • How we can make IP-telephony more energy efficient? • Conclusion & Future Work

8. IP Communication Flavors Client-Server (C/S) Peer-to-Peer (P2P)

9. IP Communication Flavors Communication Addendum Traditional Telephony Replacement

10. How Does C/S IP-Telephony Work? SIP registrar / proxy / presence server SIP registrar / proxy server IP-PSTN gateway REGISTER (ip addr) REGISTER (ip addr) (1) signaling (1) signaling (2) media (voice, video, IM) User agent User agent Utopian Internet No NATs or firewalls

11. And In The Real-World… SIP registrar / proxy / presence / server media server NAT / firewall NAT / firewall User agent User agent

12. Media Servers Bypass Firewalls SIP registrar / proxy / presence / server media server IP-PSTN gateway (1) signaling NAT / firewall NAT / firewall (1) signaling (2) media (voice, video, IM) (UDP or TCP) User agents User agents

13. How Does P2P IP-Telephony Work? media relay (or relay) node A node E NAT / firewall network address of node B? (3) media (TCP) (2) signaling (2) (4) media (1) (3) signaling P2P / PSTN gateway (1) (1) NAT / firewall network address of node E? (2) (1) node B (2) signaling • nodes form an overlay • share responsibilities for message routing, signaling, media relaying • super nodes, ordinary nodes node C node D node = user agent

14. Sources of Energy Consumption • End-point • Handsets • VoIP conversion boxes • PCs • Core • Signaling / directory • Media relaying • PSTN / mobile gateways • Network

15. Assessing Energy Consumption • Power Meters • Wattsup • Killawatt • Hardware Measurements • SIP Server • Relay Server • Desktop clients • Laptop clients • Hardware SIP phones • Software phones • Skype peers • 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

16. Outline • IP-Telephony and power consumption • Answering our questions: • Where is energy consumed? • How do different design choices effect energy consumption? • 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! Make PSTN replacement green? Reduce end-device power consumption.

18. 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.

19. media relay (or relay) NAT / firewall node A node E (3) media (TCP) (2) signaling SIP registrar / proxy / presence / server media server (1) (1) network address of node E? INVITE NAT / firewall node B (2) signaling NAT / firewall INVITE media (voice, video, IM) (UDP or TCP) node C node D User agents User agents 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.

20. media relay (or relay) NAT / firewall node A node E (3) media (TCP) (2) signaling SIP registrar / proxy / presence / server media server (1) (1) network address of node E? INVITE NAT / firewall node B (2) signaling NAT / firewall INVITE media (voice, video, IM) (UDP or TCP) node C node D User agents User agents 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?

21. 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

22. Modeling P2P and C/S • C/S model • C/S power consumption = #servers * Watts/server *redundancy factor * PUE • P2P model • S super nodes active • pssuper 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!

23. 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

24. 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: • Where is energy consumed? • How do different design choices effect energy consumption? • 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.

27. 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