15-441: Computer Networking

1. 15-441: Computer Networking Lecture 26: Where do we go from here?

2. Overview • Content is king • Billions of devices • The next billion users • “Nothing is permanent but change”

3. Named Data Networking • In the beginning... • First applications strictly focused on host-to-host interprocess communication: • Remote login, file transfer, ... • Internet was built around this host-to-host model. • Architecture is well-suited for communication between pairs of stationary hosts. • ... while today • Vast majority of Internet usage is data retrieval and service access. • Users care about the content and are oblivious to location. They are often oblivious as to delivery time: • Fetching headlines from CNN, videos from YouTube, TV from Tivo • Accessing a bank account at www.bank.com.

4. To the beginning... • What if you could re-architect the way “bulk” data transfer applications worked • HTTP • FTP • Email • etc. • ... knowing what we know now?

5. Google… Biggest content source Third largest ISP Global Crossing Level(3) Google source: ‘ATLAS’ Internet Observatory 2009 Annual Report’, C. Labovitz et.al.

6. 1995 - 2007:Textbook Internet 2009:Rise of the Hyper Giants source: ‘ATLAS’ Internet Observatory 2009 Annual Report’, C. Labovitz et.al.

7. What does the network look like… ISP ISP

8. What should the network look like… ISP ISP

9. Communication vs. Distribution

10. Overview • Content is king • Billions of devices • The next billion users • “Nothing is permanent but change”

11. Sensor Networks – Smart Devices • First introduced in late 90’s by groups at UCB/UCLA/USC • Small, resource limited devices • CPU, disk, power, bandwidth, etc. • Simple scalar sensors – temperature, motion • Single domain of deployment • farm, battlefield, bridge, rain forest • for a targeted task • find the tanks, count the birds, monitor the bridge • Ad-hoc wireless network

12. Sensor Example – Smart-Dust • Hardware • UCB motes • 4 MHz CPU • 4 kB data RAM • 128 kB code • 50 kb/sec 917 Mhz radio • Sensors: light, temp., • Sound, etc., • And a battery.

13. Sensors, Power and Radios • Limited battery life drives most goals • Radio is most energy-expensive part. • 800 instructions per bit. 200,000 instructions per packet. (!) • That’s about one message per second for ~2 months if no CPU. • Listening is expensive too. :(

14. Sensor Nets Goals • Replace communication with computation • Turn off radio receiver as often as possible • Keep little state (limited memory).

15. Power • Which uses less power? • Direct sensor  base station Tx • Total Tx power: distance^2 • Sensor  sensor  sensor  base station? • Total Tx power: n * (distance/n) ^2 =~ d^2 / n • Why? Radios are omnidirectional, but only one direction matters. Multi-hop approximates directionality. • Power savings often makes up for multi-hop capacity • These devices are *very* power constrained!

16. Example: Aggregation • Find average temperature in GHC 8th floor. • Naïve: Flood query, let a collection point compute avg. • Huge overload near the CP. Lots of loss, and local nodes use lots of energy! • Better: • Take local avg. first, & forward that. • Send average temp + # of samples • Aggregation is the key to scaling these nets. • The challenge: How to aggregate. • How long to wait? • How to aggregate complex queries? • How to program?

17. Overview • Content is king • Billions of devices • The next billion users • “Nothing is permanent but change”

18. Example Routing Problem 2 Internet City bike 3 1 Village

19. Unstated Internet Assumptions • Some path exists between endpoints • Routing finds (single) “best” existing route • E2E RTT is not very large • Max of few seconds • Window-based flow/cong ctl. work well • E2E reliability works well • Requires low loss rates • Packets are the right abstraction • Routers don’t modify packets much • Basic IP processing

20. New Challenges • Very large E2E delay • Propagation delay = seconds to minutes • Disconnected situations can make delay worse • Intermittent and scheduled links • Disconnection may not be due to failure (e.g. LEO satellite) • Retransmission may be expensive • Many specialized networks won’t/can’t run IP

21. What about TCP? • Reliable in-order delivery streams • Delay sensitive [6 timers]: • connection establishment, retransmit, persist, delayed-ACK, FIN-WAIT, (keep-alive) • Three control loops: • Flow and congestion control, loss recovery • Requires duplex-capable environment • Connection establishment and tear-down

22. Disruption Tolerant Networks

23. Disruption Tolerant Networks

24. bike (data mule) intermittent high capacity Geo satellite medium/low capacity dial-up link low capacity Routing? Village 2 City Village 1 time (days) bike bandwidth satellite phone Connectivity: Village 1 – City

25. Overview • Content is king • Billions of devices • The next billion users • “Nothing is permanent but change”

26. Other Issues • Security • Mobility as the common case • Clouds and replicated services • Evolution support…

27. Now for a message from the sponsors… • Interested in this type of stuff? • Networking group often takes students during the semester or summer • Stop by office hours or email to chat