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Cool Topics in Networking

Cool Topics in Networking. CS144 Review Session 8 November 20, 2009 Samir Selman. Announcements. Lab 5 : Due Thursday Dec 3 Final Exam: Wednesday, December 9 12:15pm - 3:15pm For those of you submitting late, contact us before your deadline if you need an additional extension. Tell us:

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Cool Topics in Networking

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  1. Cool Topics in Networking CS144 Review Session 8 November 20, 2009 Samir Selman

  2. Announcements • Lab 5 : Due Thursday Dec 3 • Final Exam: Wednesday, December 9 12:15pm - 3:15pm • For those of you submitting late, contact us before your deadline if you need an additional extension. Tell us: • Where you are • How much more time you need

  3. Today’s Cool Topics • Network Coding • Wireless Sensor Networks

  4. Current Wireless C Router

  5. Current Wireless C Router Traditional Routing requires 4time slots

  6. Current Wireless C Router Traditional Routing requires 4time slots

  7. Network Coding C Router = XOR Traditional Routing requires 4 time slots

  8. Network Coding C Router Traditional Routing requires 4 time slots

  9. Network Coding C Router = XOR = XOR Traditional Routing requires 4 time slots With Network Coding need only 3 time slots  Higher throughput

  10. I - COPE • Sachin Katti, Hariharan Rahul, Wenjun Hu, Dina Katabi, Muriel Medard, and Jon Crowcroft, "XORs In The Air: Practical Wireless Network Coding,"ACM SIGCOMM, 2006.

  11. COPE Coding Opportunities

  12. COPE Coding Opportunities

  13. II- Opportunistic Routing • Traditional routing chooses next hop before transmitting a packet. • Poor Link Quality => Probability of chosen next hop receiving packet is low • Solution: Opportunistic Routing allows any node that overhears the transmission and is closer to the destination to participate in forwarding the packet • Challenge: Multiple nodes might hear a packet broadcast and unnecessarily forward the same packet.

  14. EXOR • EXOR solves this issue by tying the MAC to the Routing and imposing a strict schedule on the routers. • The scheduler goes in rounds. Forwarders transmit in order, and only one forwarder is allowed to transmit at a given time. • Other nodes listen to learn which packets were overheard by other nodes. • Problem: This strict scheduling prevents forwarders from exploiting spatial reuse (even when multiple packets can be received by their respective receivers).

  15. MORE • Szymon Chachulski, Michael Jennings, Sachin Katti, and Dina Katabi, "Trading Structure for Randomness in Wireless Opportunistic Routing," ACM SIGCOMM, 2007

  16. MORE • MORE solves the problem with Opportunistic Coding without tying Routing to the MAC. • Instead it uses Network Coding + Randomness. • Basically nodes randomly mix packets before forwarding them. • This ensures the routers hearing the same transmission do not forward the same packet.

  17. MORE - Examples Unicast Case • Src sends P1,P2 • Dest luckily overhears P1. • Router doesn’t know what dest received (P1). • In any case R can forward P1 + 2P2 • Dest now has two received packets • P1 • P1 + 2P2 • Dest can solve 2 eqns with 2 unknowns to retrieve P2. • Conclusion: R only forwarded one packet instead of two =>Higher throughput

  18. MORE - Examples Multicast Case • Without Network Coding, src has to retransmit the union of the lost packets ( 4 pkts ). • With Network coding can retransmit only 2 randomly coded pkts and allow all destinations to decode their respective packets. • Src retransmits pa = p1+ p2 + p3 + p4, and pb= p1 + 2p2 + 3p3 + 4p4.

  19. Analog Network Coding • Sachin Katti, Shyamnath Gollakota, and Dina Katabi, "Embracing Wireless Interference: Analog Network Coding," ACM SIGCOMM, 2007.

  20. Analog Network Coding Analog Network Coding (ANC) Instead of router mixing packets… Exploit that the wireless channelnaturally mixes signals

  21. Analog Network Coding C Router

  22. Analog Network Coding C Router Interference Phil and David transmit simultaneously

  23. Analog Network Coding C Router Phil and David transmit simultaneously Router amplifies and broadcasts interfered signal

  24. Analog Network Coding C Router Phil and David transmit simultaneously Router amplifies and broadcasts interfered signal Phil subtracts known signal from interfered signal

  25. Analog Network Coding C Router Dina and Robert transmit simultaneously Router amplifies and broadcasts interfered signal Dina subtracts known signal from interfered signal • Analog Network Coding requires 2 time slots • Higher throughput

  26. It Is More Than Going From 3 To 2! • Philosophical shift in dealing with interference • Strategically exploit interference instead of avoiding it • Promises new ways of dealing with hidden terminals

  27. Hidden Terminal Scenario C C C C Src R2 R1 Dst

  28. Hidden Terminal Scenario C C C C Src R2 R1 Dst P1

  29. Hidden Terminal Scenario C C C C Src R2 R1 Dst P1 P2 Src and R2 transmit simultaneously

  30. Hidden Terminal Scenario C C C C Src R2 R1 Dst P1 P2 Src and R2 transmit simultaneously R1 subtracts P1, which he relayed earlier to recover P2 that he wants

  31. Hidden Terminal Scenario C C C C Src R2 R1 Dst P1 P2 • R2 and Src are hidden terminals • Today : Simultaneous transmission  Collision • ANC : Simultaneous transmission  Success!

  32. Hidden Terminal Scenario C C C C Src R2 R1 Dst • Other Benefits of ANC: • First step toward addressing hidden terminals • ANC extends network coding to new scenarios

  33. Wireless Sensor Networks • A sensor network is an Ad-hoc network composed of densely populated tiny electronic sensing devices. • Basic function of the network is to observe some phenomenon. • Characteristics: • Low cost, Low power, Light weight • Densely deployed • Prone to failures • Two ways of deployment: randomly, pre-determined • Objectives: • Monitor Activities • Gather and fuse information • Communicate it to special node “Base Station”.

  34. Computer Revolution Original IBM PC (1981) MICAZ Mote (2005) 4.77 MHz 4 MHz 16-256 KB RAM 128 KB RAM 160 KB Floppies 512 KB Flash ~ $6K (today) ~ $35 ~ 64 W ~14 mW 25 lb, 19.5 x 5.5 x 16 inch 0.5 oz, 2.25 x 1.25 x 0.25 inch

  35. Sensor Node Hardware Platform

  36. Software Platform

  37. WSN Applications

  38. WSN Applications

  39. WSN Applications

  40. WSN Applications

  41. WSN Applications

  42. WSN protocols Protocol Requirements: • Energy Efficient (Maximize node lifetime) • Self Configuring • Scalable • Redundant • Efficient (less computation, less memory requirements, less energy consumption…) • Robust

  43. Energy Efficiency • Sources of Energy Consumption: • Communications (Transmitting & Receiving) • Computations • Sensing • Sources of Energy Wastage in Communications: • Collisions • Overhearing • Idle Listening • Control Packets overhead • Over emitting

  44. WSN Protocol Research

  45. Questions?

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