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State of Multi-Hop Wireless Networking

State of Multi-Hop Wireless Networking

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State of Multi-Hop Wireless Networking

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  1. State of Multi-Hop Wireless Networking Nitin Vaidya Electrical and Computer Engineering University of Illinois at Urbana-Champaign Sept. 15. 2008

  2. Calvin (and Hobbes) : Bill Watterson So the secret to good self-esteem is to lower your expectations to the point where they're already met ? Deep Thought

  3. Caveat This talk is based on opinions not necessarily substantiated by real data

  4. Multi-Hop Wireless • Many possibilities …

  5. Multi-Hop Wireless • Mobile ad hoc networks • Interconnect cars, planes,tanks, soldiers, people

  6. Multi-Hop Wireless • Mesh networks (roof-top, pole-top) internet Mesh Client

  7. Multi-Hop Wireless • Sensor networks

  8. Multi-Hop Wireless • OpportunisticDelay/Disruption/Disconnection-tolerant networks

  9. Why Multi-Hop Wireless ?

  10. Why Multi-Hop Wireless ? • Lack of infrastructure

  11. Why Multi-Hop Wireless ? • Some clients difficult to reach directly via infrastructure, due to obstacles AP Relay

  12. Why Multi-Hop Wireless ? • Decreasing dependence on wired infrastructure • Add wireless “infrastructure” internet Mesh Client

  13. Why Multi-Hop Wireless ? • Low-power clients unable to communicate directly with infrastructure

  14. Why Multi-Hop Wireless ? • For improved capacity High transmit power High interference

  15. Why Multi-Hop Wireless ? • For improved capacity Low transmit power Low interference

  16. Why Multi-Hop Wireless ? • Poor connectivity

  17. A Selective History 1973-87 DARPA Packet Radio Networks (PRNET/SURAN) 1997 IEEE 802.11 1997 IETF MANET 1999 TinyOS 2000 MeshNetworks founded 2000+ CUWiN open-source mesh 2000 ACM MobiHoc 2001 “Embedded, Everywhere”  Sensor networks 2001 Interplanetary Internet, IETF draft, Vint Cerf 2003 ACM Sensys 2004 Motorola acquires MeshNetworks 2004 IEEE 802.11s study group for mesh networking 2004 ZigBee Time

  18. Research ActivityversusRelevance

  19. Research Activity Much activity in • Mobile ad hoc networks • No infrastructure • Large diameter • High mobility • Sensor networks • Low power • Large diameter • Small diameter useful in practice, but not “interesting”

  20. Unscientific Measure of Interest:Google 9/11/08 • Ad hoc networks: 2,290,000 • Mesh networks: 764,000 • Sensor networks: 1,670,000 • Vehicular networks: 1,710,000 • Delay tolerant networks: 196,000 • Disruption tolerant networks: 206,000 • Disconnection tolerant networks: 99,800 • Opportunistic networks: 978,000 Magna Carta (1215)2,630,000 United states constitution (1787) 5,790,000 Computerarchitecture21,400,000 802.1166,000,000 Paris Hilton 68,800,000

  21. Research Activity Most activity seems to be in • Mobile ad hoc networks • No infrastructure • Large diameter • High mobility • Sensor networks • Low power • Large diameter Extreme assumptions make the problem exciting But what about relevance ?

  22. Relevance ?

  23. Relevance • Not all networks are made equal … • Some are likely to be commonplaceothers limited to niche scenarios Relevance In increasing order of relevance …

  24. Delay Tolerant Networks • Limited to niche scenarios

  25. Interesting Variation • Wireless Graffiti • Microblogs • “Sticky notes in-the-air” Users leave information “in the air” at some location Others can retrieve later from there May be viewed as opportunistic communication (Not quite the same as DTN)

  26. Mobile Ad Hoc Networks • Why design networks without infrastructure ? • Possible to deploy some infrastructure inmost environments

  27. Sensor Networks • Wireless sensors are important • Important to network the sensors • Sensors + Network ≠Large diameter

  28. Infrastructure Extension • Most compelling reason for multi-hop wireless  Only a small number of hops! AP Relay

  29. Infrastructure Extension • Mesh (Wireless “infrastructure”) internet

  30. Summary:Most Appealing Scenario • Some wired infrastructure  Capacity scales with the infrastructure • Small diameter wireless extensionfor the infrastructure Using relays or peer-to-peer  Better reachability  Low-power operation  Reduced capacity loss

  31. If only small diameter networks matter,did we waste our time ? Not quite … • Interference management and MAC-related issuessomewhat independent of network diameter

  32. State of Multi-Hop Wireless Very large volume of activity • Beautiful theory Asymptotic Capacity Throughput-optimal scheduling Network utility optimization Network coding Cooperative relaying

  33. State of Multi-Hop Wireless Very large volume of activity • Practical protocols & deployments Many wireless standards And many more MAC & routing protocols Many experimental deployments Mesh devices Sensor devices Start-ups

  34. State of Multi-Hop Wireless Very large volume of activity • (Too) Many conferences and workshops • Plenty of research funding Compared to many other areas

  35. State of Multi-Hop Wireless Despite the volume of activity • Difficult to enumerate core set of principles for wireless network design What should we teach in an undergraduate wireless networks class ?

  36. State of Multi-Hop Wireless Despite the volume of activity • Theoretical developments haven’t been translated to practice • Much protocol design ignores physical layer issues Much talk of cross-layer design, but progress not impressive

  37. What is Lacking ? Meaningful contact between • Practice • Networking Theory Comm Picture from Wikipedia

  38. capacity User Applications Multi-channel protocol channels Capacity bounds Insights on protocol design Fixed D IP Stack OS improvements Software architecture Net-X testbed F B ARP E Switchable A Channel Abstraction Module C Interface Device Driver Interface Device Driver CSL Net-XTheory to Practice Linux box

  39. Things I Wish I Had Learned in Kindergarten

  40. outgrow 1 Those who cannot learn from historyare doomed to repeat it With apologies to George Santayana

  41. Pre-History of Wireless Communication:Smoke Signals, Fires, Semaphore Relaying : Multi-hop routes (store-and-forward)

  42. Pre-History of Wireless Communication:Homing Pigeons Exploiting mobility

  43. Reusing Ideas Reasonable,but Need to Explore Better Alternatives No wired-equivalent for wireless networks No links !

  44. Wireless Channel Offers Rich Diversity Current protocols exploit diversity only to a limited extent Layer 1 : 2+ gap The vanishing link : Diversity confuses the notion of a link

  45. 2 Interference is Information

  46. B A D C Interference is Information Signal Interference

  47. 3 Bits Are Not Automobiles

  48. Bits Are Not Automobiles • We treat information networks same asphysical transportation networks • Planes, Trains and Automobiles • Bits can be combined (encoded) andseparated, unlike physical objects

  49. Q P Network Coding A B C Q P

  50. + Q P +Q P Q Network Coding A B C Q P