“ Open” Problems in Mobile Ad Hoc Networking Nitin Vaidya University of Illinois at Urbana-Champaign [email_address] www.c...
Mobile Ad Hoc Networks <ul><li>Formed by wireless hosts which may be mobile </li></ul><ul><li>Without necessarily using a ...
Mobile Ad Hoc Networks <ul><li>May need to traverse multiple links to reach a destination </li></ul>
Mobile Ad Hoc Networks (MANET) <ul><li>Mobility causes route changes </li></ul>
Why Ad Hoc Networks ? <ul><li>Potential ease of deployment </li></ul><ul><li>Decreased dependence on infrastructure </li><...
Many Applications <ul><li>Personal area networking </li></ul><ul><ul><li>cell phone, laptop, ear phone, wrist watch </li><...
Many Variations <ul><li>Fully Symmetric Environment </li></ul><ul><ul><li>all nodes have identical  capabilities  and   re...
Many Variations <ul><li>Traffic characteristics may differ in different ad hoc networks </li></ul><ul><ul><li>bit rate </l...
Many Variations <ul><li>Mobility patterns may be different </li></ul><ul><ul><li>people sitting at an airport lounge </li>...
Challenges <ul><li>Limited wireless transmission range </li></ul><ul><li>Broadcast nature of the wireless medium </li></ul...
Research on Mobile Ad Hoc Networks <ul><li>Variations in capabilities & responsibilities </li></ul><ul><li>X </li></ul><ul...
Hidden Terminals & RTS/CTS Handshake
Hidden Terminal Problem <ul><li>Node B can communicate with A and C both </li></ul><ul><li>A and C cannot hear each other ...
RTS/CTS Handshake <ul><li>Sender sends Ready-to-Send (RTS)  </li></ul><ul><li>Receiver responds with Clear-to-Send (CTS)  ...
Problems in Ad Hoc Networking
Problem Space <ul><li>Practical considerations </li></ul><ul><ul><li>Consumer demand or lack thereof </li></ul></ul><ul><u...
Problem Space Link Network Transport Physical Upper layers
Physical Layer
Physical Layer <ul><li>Traditionally, not much interaction between physical layer and upper layers </li></ul><ul><li>Many ...
Adaptive Modulation <ul><li>Channel conditions are time-varying </li></ul>A B
<ul><li>Choose modulation scheme as a function of channel conditions </li></ul>
Adaptive Modulation <ul><li>If physical layer chooses the modulation scheme transparent to MAC </li></ul><ul><ul><li>  MA...
Sender-Based  “Autorate Fallback” MAC Protocol <ul><li>Sender decreases rate after  N  consecutive ACKS are not received <...
Performance of Sender-Based “Autorate Fallback” Expected ARF CCK (11Mbps) CCK (5.5Mbps) QPSK (2Mbps) BPSK (1Mbps)
<ul><li>Sender sends RTS containing its  best rate estimate </li></ul><ul><li>Receiver chooses best rate for the condition...
Physical Layer <ul><li>Several other physical layer capabilities call for changes to upper layers of protocol stack </li><...
Power Control <ul><li>Transmit power determines </li></ul><ul><ul><li>“Range” of a transmission </li></ul></ul><ul><ul><li...
Power Control <ul><li>Transmit power determines </li></ul><ul><ul><li>“Range” of a transmission </li></ul></ul><ul><ul><li...
Benefits of Power Control <ul><li>Transmit a packet with least transmit power necessary to deliver to the receiver </li></...
Power Control <ul><li>Power control introduces asymmetry </li></ul><ul><li>D transmits to C at low power, but B uses high ...
Power Control <ul><li>Proposals for medium access control and routing with power control exist </li></ul><ul><li>Do not so...
Directional / Smart Antennas <ul><li>Various capabilities </li></ul><ul><ul><li>Sectored antennas (fixed beam positions) <...
Physical Layer <ul><li>Are ad hoc networks benefiting from the progress made at physical layer ? </li></ul><ul><li>Other i...
Physical Layer: Simulation Models <ul><li>Insufficient accuracy in commonly used physical layer models </li></ul><ul><li>P...
Link Layer
Interesting Link Layer Issues <ul><li>Medium access control </li></ul><ul><li>Retransmission mechanisms </li></ul><ul><li>...
QoS in Medium Access Control <ul><li>Many proposals for achieving  fairness </li></ul><ul><li>Fair scheduling  schemes att...
QoS in MAC <ul><li>Easier in a centralized protocol (such as 802.11 point coordination function), than in a distributed pr...
Transmission Scheduling <ul><li>When multiple packets pending transmission, which packet to transmit next? </li></ul><ul><...
MAC for Multiple Channels <ul><li>How to split bandwidth into channels? </li></ul><ul><li>How to use the multiple channels...
Network Layer
Reactive versus Proactive Routing <ul><li>Reactive protocols </li></ul><ul><ul><li>Maintain routes between nodes that need...
Routing <ul><li>Reactive and proactive protocols are quite  </li></ul><ul><li>well-understood </li></ul><ul><li>Designing ...
Reactive versus Proactive <ul><li>Choice of protocol depends on </li></ul><ul><ul><li>Mobility characteristics of the node...
Reactive versus Proactive <ul><li>Need a more flexible way to manage protocol behavior </li></ul><ul><li>Assign proactive/...
Address Assignment <ul><li>How to assign addresses to nodes in an ad hoc network ? </li></ul><ul><li>Static assignment </l...
Transport Protocols
TCP <ul><li>TCP performance degrades in presence of route failures </li></ul><ul><li>TCP cannot distinguish between packet...
TCP <ul><li>Several solutions have been proposed to fix this </li></ul><ul><li>These techniques somehow inform TCP sender ...
TCP <ul><li>New route may differ significantly from old route </li></ul><ul><li>Proposals for TCP-over-ad-hoc tend to use ...
Other Issues
Algorithms
Distributed Algorithms <ul><li>Rich body of work on distributed algorithms in traditional distributed environments </li></...
Distributed Algorithms <ul><li>Existing algorithms can usually be used on ad hoc networks without affecting  correctness <...
Distributed Algorithms <ul><li>How to design distributed algorithm exploiting the correlation between mobility and link fa...
Distributed Algorithms <ul><li>Traditionally, complexity is measured as a function of problem “size”  </li></ul><ul><ul><l...
Security Issues
What’s New ? <ul><li>Wireless medium easy to snoop on </li></ul><ul><li>With ad hoc networking, hard to guarantee connecti...
Authentication <ul><li>How to authenticate a node ? </li></ul><ul><li>May not have access to a certification authority </l...
Resource Depletion Attack <ul><li>Intruders may send data with the objective of congesting a network or depleting batterie...
Routing Attacks <ul><li>Intruders may mis-route the data </li></ul><ul><ul><li>not delivering it to the destination at all...
Traffic Analysis <ul><li>Despite encryption, an eavesdropper can identify traffic patterns </li></ul><ul><li>Traffic patte...
Other Issues
Incentives for Ad Hoc Routing <ul><li>Why should I forward packets for some other nodes ? </li></ul><ul><li>Need some ince...
Applications <ul><li>New applications for ad hoc networks ? </li></ul>
Hybrid Environments <ul><li>Use infrastructure when convenient </li></ul><ul><li>Use ad hoc connectivity when necessary or...
Summary
Summary <ul><li>Plenty of interesting research problems </li></ul><ul><li>Research community disproportionately obsessed w...
Summary <ul><li>Interesting problems elsewhere at the two ends of the protocol stack </li></ul><ul><li>How to design  </li...
Summary <ul><li>Hybrid environments require revisiting protocol design decisions </li></ul>
Tutorials <ul><li>Visit  http://www.crhc.uiuc.edu/~nhv   for my tutorials on </li></ul><ul><ul><li>Mobile ad hoc networkin...
Thank you !! Comments/questions to [email_address] © 2001 Nitin Vaidya
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  • RTS/CTS serves two purposes quicker retransmissions if there is a collision because there is no collision detection avoids collisions caused by hidden terminals
  • Our work: How to integrate adaptive modulation with 802.11 medium access control ?
  • "Open" Problems in Mobile Ad Hoc Networking

    1. 1. “ Open” Problems in Mobile Ad Hoc Networking Nitin Vaidya University of Illinois at Urbana-Champaign [email_address] www.crhc.uiuc.edu/~nhv Keynote talk presented at the Workshop on Wireless Local Networks (in conjunction with 26 th Conference on Local Computer Networks), Tampa, Florida, November 14, 2001 © 2001 Nitin Vaidya
    2. 2. Mobile Ad Hoc Networks <ul><li>Formed by wireless hosts which may be mobile </li></ul><ul><li>Without necessarily using a pre-existing infrastructure </li></ul><ul><li>Routes between nodes may potentially contain multiple hops </li></ul>
    3. 3. Mobile Ad Hoc Networks <ul><li>May need to traverse multiple links to reach a destination </li></ul>
    4. 4. Mobile Ad Hoc Networks (MANET) <ul><li>Mobility causes route changes </li></ul>
    5. 5. Why Ad Hoc Networks ? <ul><li>Potential ease of deployment </li></ul><ul><li>Decreased dependence on infrastructure </li></ul>
    6. 6. Many Applications <ul><li>Personal area networking </li></ul><ul><ul><li>cell phone, laptop, ear phone, wrist watch </li></ul></ul><ul><li>Military environments </li></ul><ul><ul><li>soldiers, tanks, planes </li></ul></ul><ul><li>Civilian environments </li></ul><ul><ul><li>taxi cab network </li></ul></ul><ul><ul><li>meeting rooms </li></ul></ul><ul><ul><li>sports stadiums </li></ul></ul><ul><ul><li>boats, small aircraft </li></ul></ul><ul><li>Emergency operations </li></ul><ul><ul><li>search-and-rescue </li></ul></ul><ul><ul><li>policing and fire fighting </li></ul></ul>
    7. 7. Many Variations <ul><li>Fully Symmetric Environment </li></ul><ul><ul><li>all nodes have identical capabilities and responsibilities </li></ul></ul><ul><li>Asymmetric Capabilities </li></ul><ul><ul><li>transmission ranges and radios may differ </li></ul></ul><ul><ul><li>battery life at different nodes may differ </li></ul></ul><ul><ul><li>processing capacity may be different at different nodes </li></ul></ul><ul><ul><li>speed of movement </li></ul></ul><ul><li>Asymmetric Responsibilities </li></ul><ul><ul><li>only some nodes may route packets </li></ul></ul><ul><ul><li>some nodes may act as leaders of nearby nodes (e.g., cluster head) </li></ul></ul>
    8. 8. Many Variations <ul><li>Traffic characteristics may differ in different ad hoc networks </li></ul><ul><ul><li>bit rate </li></ul></ul><ul><ul><li>timeliness constraints </li></ul></ul><ul><ul><li>reliability requirements </li></ul></ul><ul><ul><li>unicast / multicast / geocast </li></ul></ul><ul><ul><li>host-based addressing / content-based addressing / capability-based addressing </li></ul></ul><ul><li>May co-exist (and co-operate) with an infrastructure-based network </li></ul>
    9. 9. Many Variations <ul><li>Mobility patterns may be different </li></ul><ul><ul><li>people sitting at an airport lounge </li></ul></ul><ul><ul><li>New York taxi cabs </li></ul></ul><ul><ul><li>kids playing </li></ul></ul><ul><ul><li>military movements </li></ul></ul><ul><ul><li>personal area network </li></ul></ul><ul><li>Mobility characteristics </li></ul><ul><ul><li>speed </li></ul></ul><ul><ul><li>predictability </li></ul></ul><ul><ul><ul><li>direction of movement </li></ul></ul></ul><ul><ul><ul><li>pattern of movement </li></ul></ul></ul><ul><ul><li>uniformity (or lack thereof) of mobility characteristics among different nodes </li></ul></ul>
    10. 10. Challenges <ul><li>Limited wireless transmission range </li></ul><ul><li>Broadcast nature of the wireless medium </li></ul><ul><ul><ul><ul><li>Hidden terminal problem </li></ul></ul></ul></ul><ul><li>Packet losses due to transmission errors </li></ul><ul><li>Mobility-induced route changes </li></ul><ul><li>Mobility-induced packet losses </li></ul><ul><li>Battery constraints </li></ul><ul><li>Potentially frequent network partitions </li></ul><ul><li>Ease of snooping on wireless transmissions (security hazard) </li></ul>
    11. 11. Research on Mobile Ad Hoc Networks <ul><li>Variations in capabilities & responsibilities </li></ul><ul><li>X </li></ul><ul><li>Variations in traffic characteristics, mobility models, etc. </li></ul><ul><li>X </li></ul><ul><li>Performance criteria (e.g., optimize throughput, reduce energy consumption) </li></ul><ul><li>+ </li></ul><ul><li>Increased research funding </li></ul><ul><li>= </li></ul><ul><li>Significant research activity </li></ul>
    12. 12. Hidden Terminals & RTS/CTS Handshake
    13. 13. Hidden Terminal Problem <ul><li>Node B can communicate with A and C both </li></ul><ul><li>A and C cannot hear each other </li></ul><ul><li>When A transmits to B, C cannot detect the transmission using the carrier sense mechanism </li></ul><ul><li>If C transmits, collision will occur at node B </li></ul>A B C
    14. 14. RTS/CTS Handshake <ul><li>Sender sends Ready-to-Send (RTS) </li></ul><ul><li>Receiver responds with Clear-to-Send (CTS) </li></ul><ul><li>RTS and CTS announce the duration of the transfer </li></ul><ul><li>Nodes overhearing RTS/CTS keep quiet for that duration </li></ul><ul><li>RTS/CTS used in IEEE 802.11 </li></ul>D C B A 10 10 CTS (10) RTS (10)
    15. 15. Problems in Ad Hoc Networking
    16. 16. Problem Space <ul><li>Practical considerations </li></ul><ul><ul><li>Consumer demand or lack thereof </li></ul></ul><ul><ul><li>Standardization </li></ul></ul><ul><ul><li>Government regulations </li></ul></ul><ul><li>Technical issues </li></ul>
    17. 17. Problem Space Link Network Transport Physical Upper layers
    18. 18. Physical Layer
    19. 19. Physical Layer <ul><li>Traditionally, not much interaction between physical layer and upper layers </li></ul><ul><li>Many physical layer mechanisms not beneficial without help from upper layers </li></ul><ul><li>Example : Adaptive modulation </li></ul>
    20. 20. Adaptive Modulation <ul><li>Channel conditions are time-varying </li></ul>A B
    21. 21. <ul><li>Choose modulation scheme as a function of channel conditions </li></ul>
    22. 22. Adaptive Modulation <ul><li>If physical layer chooses the modulation scheme transparent to MAC </li></ul><ul><ul><li> MAC cannot know the time duration required for the transfer </li></ul></ul><ul><li>Must involve MAC protocol in deciding the modulation scheme </li></ul><ul><ul><li>Some 802.11-compliant implementations use a sender-based scheme for this purpose </li></ul></ul><ul><ul><li>Receiver-based schemes can perform better </li></ul></ul>
    23. 23. Sender-Based “Autorate Fallback” MAC Protocol <ul><li>Sender decreases rate after N consecutive ACKS are not received </li></ul><ul><li>Sender increases rate after Y consecutive ACKS are received </li></ul>D C B A 1Mbps 2Mbps DATA 2Mbps
    24. 24. Performance of Sender-Based “Autorate Fallback” Expected ARF CCK (11Mbps) CCK (5.5Mbps) QPSK (2Mbps) BPSK (1Mbps)
    25. 25. <ul><li>Sender sends RTS containing its best rate estimate </li></ul><ul><li>Receiver chooses best rate for the conditions and sends it in the CTS </li></ul><ul><li>Sender transmits DATA packet at new rate </li></ul><ul><li>Information in data packet header implicitly updates nodes that heard old rate </li></ul>Receiver-Based Autorate MAC Protocol 1Mbps 2Mbps D C B A 2 1 CTS (1) RTS (2)
    26. 26. Physical Layer <ul><li>Several other physical layer capabilities call for changes to upper layers of protocol stack </li></ul><ul><li>Example: Power control </li></ul>
    27. 27. Power Control <ul><li>Transmit power determines </li></ul><ul><ul><li>“Range” of a transmission </li></ul></ul><ul><ul><li>Interference caused at other nodes </li></ul></ul>B C D A
    28. 28. Power Control <ul><li>Transmit power determines </li></ul><ul><ul><li>“Range” of a transmission </li></ul></ul><ul><ul><li>Interference caused at other nodes </li></ul></ul>B C D A
    29. 29. Benefits of Power Control <ul><li>Transmit a packet with least transmit power necessary to deliver to the receiver </li></ul><ul><ul><li>Save energy : Important benefit to battery-powered hosts </li></ul></ul><ul><ul><li>Reduce interference </li></ul></ul><ul><ul><li>Can allow greater spatial reuse </li></ul></ul>
    30. 30. Power Control <ul><li>Power control introduces asymmetry </li></ul><ul><li>D transmits to C at low power, but B uses high transmit power to transmit to A </li></ul><ul><li>B may not about D-to-C transmission, but can interfere with it </li></ul>B C D A
    31. 31. Power Control <ul><li>Proposals for medium access control and routing with power control exist </li></ul><ul><li>Do not solve the problem satisfactorily </li></ul><ul><li>Ideal solution will </li></ul><ul><ul><li>Reduce energy consumption, and </li></ul></ul><ul><ul><li>Maximize spatial reuse </li></ul></ul>
    32. 32. Directional / Smart Antennas <ul><li>Various capabilities </li></ul><ul><ul><li>Sectored antennas (fixed beam positions) </li></ul></ul><ul><ul><li>Beam steering </li></ul></ul><ul><ul><li>Tracking a transmitter </li></ul></ul><ul><li>MAC and routing protocols for ad hoc networks using such antennas </li></ul><ul><li>How to take into account antenna capabilities? </li></ul><ul><ul><ul><li>Network may be heterogeneous </li></ul></ul></ul>
    33. 33. Physical Layer <ul><li>Are ad hoc networks benefiting from the progress made at physical layer ? </li></ul><ul><li>Other interesting areas </li></ul><ul><ul><li>Efficient coding schemes </li></ul></ul><ul><ul><li>Various diversity techniques </li></ul></ul>
    34. 34. Physical Layer: Simulation Models <ul><li>Insufficient accuracy in commonly used physical layer models </li></ul><ul><li>Physical link state is not binary as often assumed </li></ul><ul><li>Reliable packet reception does not depend just on distance </li></ul><ul><ul><li>Transmit power </li></ul></ul><ul><ul><li>Interference level </li></ul></ul><ul><ul><li>Fading </li></ul></ul><ul><li>Need to use realistic models </li></ul><ul><ul><li>Modulation scheme </li></ul></ul><ul><ul><li>Coding </li></ul></ul>
    35. 35. Link Layer
    36. 36. Interesting Link Layer Issues <ul><li>Medium access control </li></ul><ul><li>Retransmission mechanisms </li></ul><ul><li>Transmission scheduling </li></ul><ul><ul><li>Which pending packet should a node attempt to transmit? </li></ul></ul><ul><li>Adaptive parameter selection </li></ul><ul><ul><li>Frame size </li></ul></ul><ul><ul><li>Retransmission limit </li></ul></ul>
    37. 37. QoS in Medium Access Control <ul><li>Many proposals for achieving fairness </li></ul><ul><li>Fair scheduling schemes attempt to provide equitable sharing of channel </li></ul><ul><li>Unpredictable nature of transmission errors makes it difficult to make hard guarantees </li></ul><ul><li>Need to develop a probabilistic framework </li></ul>
    38. 38. QoS in MAC <ul><li>Easier in a centralized protocol (such as 802.11 point coordination function), than in a distributed protocol </li></ul><ul><li>Distributed MAC appears more suitable for ad hoc networks, however </li></ul><ul><li>Perhaps a hybrid protocol will be best </li></ul><ul><ul><li>How to design such a protocol ? </li></ul></ul>
    39. 39. Transmission Scheduling <ul><li>When multiple packets pending transmission, which packet to transmit next? </li></ul><ul><li>Choice should depend on </li></ul><ul><ul><li>Receiver status (blocked by some other transmission?) </li></ul></ul><ul><ul><li>Congestion at receivers </li></ul></ul><ul><ul><li>Noise level at receivers </li></ul></ul><ul><ul><li>Tolerable delay for pending packets </li></ul></ul><ul><ul><ul><ul><li>Need interaction between upper layers and MAC </li></ul></ul></ul></ul>
    40. 40. MAC for Multiple Channels <ul><li>How to split bandwidth into channels? </li></ul><ul><li>How to use the multiple channels ? </li></ul><ul><ul><ul><li>Dedicated channel for control ? </li></ul></ul></ul>
    41. 41. Network Layer
    42. 42. Reactive versus Proactive Routing <ul><li>Reactive protocols </li></ul><ul><ul><li>Maintain routes between nodes that need to communicate </li></ul></ul><ul><li>Proactive protocols </li></ul><ul><ul><li>Maintain routes between all node-pairs </li></ul></ul><ul><li>Lot of activity on routing protocol design </li></ul>
    43. 43. Routing <ul><li>Reactive and proactive protocols are quite </li></ul><ul><li>well-understood </li></ul><ul><li>Designing reactive protocols: “Solved” problem </li></ul><ul><li>Designing proactive protocols: “Solved” problem </li></ul><ul><ul><li>At least, when using common assumptions about the network </li></ul></ul><ul><ul><li>Interesting problems exist when other issues are considered (such as QoS or physical layer properties) </li></ul></ul>
    44. 44. Reactive versus Proactive <ul><li>Choice of protocol depends on </li></ul><ul><ul><li>Mobility characteristics of the nodes </li></ul></ul><ul><ul><li>Traffic characteristics </li></ul></ul><ul><li>How to design adaptive protocols ? </li></ul><ul><li>Existing proposals use a straightforward combination of reactive and proactive </li></ul><ul><ul><li>Proactive within “radius” K </li></ul></ul><ul><ul><li>Reactive outside K </li></ul></ul><ul><ul><li>Choose K somehow </li></ul></ul>
    45. 45. Reactive versus Proactive <ul><li>Need a more flexible way to manage protocol behavior </li></ul><ul><li>Assign proactive/reactive tag to each route (A,B) ? </li></ul><ul><li>How to determine when proactive behavior is better than reactive ? </li></ul>
    46. 46. Address Assignment <ul><li>How to assign addresses to nodes in an ad hoc network ? </li></ul><ul><li>Static assignment </li></ul><ul><ul><li>Easier to guarantee unique address </li></ul></ul><ul><li>Dynamic assignment </li></ul><ul><ul><li>How to guarantee unique addresses when partitions merge? </li></ul></ul><ul><li>Do we need to guarantee unique addresses ? </li></ul>
    47. 47. Transport Protocols
    48. 48. TCP <ul><li>TCP performance degrades in presence of route failures </li></ul><ul><li>TCP cannot distinguish between packet losses due to route change and due to congestion </li></ul><ul><li>Reduces congestion window in response </li></ul><ul><ul><ul><li>Unnecessary degradation in throughput </li></ul></ul></ul>
    49. 49. TCP <ul><li>Several solutions have been proposed to fix this </li></ul><ul><li>These techniques somehow inform TCP sender that the packet losses are due to route failure </li></ul><ul><li>TCP does not decrease congestion window in response </li></ul>
    50. 50. TCP <ul><li>New route may differ significantly from old route </li></ul><ul><li>Proposals for TCP-over-ad-hoc tend to use old timeout and congestion window after a route change </li></ul><ul><li>Does not seem like a good idea </li></ul><ul><li>How to choose appropriate timeout and congestion window after detecting a route change ? </li></ul>
    51. 51. Other Issues
    52. 52. Algorithms
    53. 53. Distributed Algorithms <ul><li>Rich body of work on distributed algorithms in traditional distributed environments </li></ul><ul><ul><li>Shared memory </li></ul></ul><ul><ul><li>Message ordering </li></ul></ul><ul><ul><li>Clock synchronization </li></ul></ul><ul><ul><li>Leader election </li></ul></ul>
    54. 54. Distributed Algorithms <ul><li>Existing algorithms can usually be used on ad hoc networks without affecting correctness </li></ul><ul><li>Performance on ad hoc networks may not be good </li></ul><ul><li>Existing algorithm treat link repairs/failures as random events </li></ul><ul><li>With mobility, link failure/repairs are correlated with host movement </li></ul>
    55. 55. Distributed Algorithms <ul><li>How to design distributed algorithm exploiting the correlation between mobility and link failure/repair ? </li></ul>
    56. 56. Distributed Algorithms <ul><li>Traditionally, complexity is measured as a function of problem “size” </li></ul><ul><ul><li>Number of nodes </li></ul></ul><ul><ul><li>Number of failures </li></ul></ul><ul><li>How to analyze algorithm complexity as a function of mobility ? </li></ul><ul><li>What measure of mobility is amenable to such an analysis ? </li></ul><ul><ul><li>Need to capture the correlation without making the measure too complex </li></ul></ul>
    57. 57. Security Issues
    58. 58. What’s New ? <ul><li>Wireless medium easy to snoop on </li></ul><ul><li>With ad hoc networking, hard to guarantee connectivity </li></ul><ul><li>Easier for intruders to insert themselves into network </li></ul>
    59. 59. Authentication <ul><li>How to authenticate a node ? </li></ul><ul><li>May not have access to a certification authority </li></ul>
    60. 60. Resource Depletion Attack <ul><li>Intruders may send data with the objective of congesting a network or depleting batteries </li></ul>A C B D T intruder U intruder Bogus traffic
    61. 61. Routing Attacks <ul><li>Intruders may mis-route the data </li></ul><ul><ul><li>not delivering it to the destination at all, or </li></ul></ul><ul><ul><li>delaying it significantly </li></ul></ul><ul><li>How to detect such attacks ? </li></ul><ul><li>How to tolerate such attacks ? </li></ul>
    62. 62. Traffic Analysis <ul><li>Despite encryption, an eavesdropper can identify traffic patterns </li></ul><ul><li>Traffic patterns can divulge information about the operation mode </li></ul><ul><li>Traffic analysis can be prevented by presenting “constant” traffic pattern </li></ul><ul><ul><ul><ul><li>Insert dummy traffic </li></ul></ul></ul></ul><ul><li>How to make this cheaper ? </li></ul>
    63. 63. Other Issues
    64. 64. Incentives for Ad Hoc Routing <ul><li>Why should I forward packets for some other nodes ? </li></ul><ul><li>Need some incentive mechanism </li></ul><ul><li>Policies to determine reward for performing each operation </li></ul>
    65. 65. Applications <ul><li>New applications for ad hoc networks ? </li></ul>
    66. 66. Hybrid Environments <ul><li>Use infrastructure when convenient </li></ul><ul><li>Use ad hoc connectivity when necessary or superior </li></ul>E A BS1 BS2 X Z infrastructure Ad hoc connectivity
    67. 67. Summary
    68. 68. Summary <ul><li>Plenty of interesting research problems </li></ul><ul><li>Research community disproportionately obsessed with routing protocols </li></ul>
    69. 69. Summary <ul><li>Interesting problems elsewhere at the two ends of the protocol stack </li></ul><ul><li>How to design </li></ul><ul><li>algorithms and applications ? </li></ul><ul><li>How to exploit physical </li></ul><ul><li>layer techniques ? </li></ul><ul><ul><ul><li>Increase interaction </li></ul></ul></ul><ul><ul><ul><li>between physical layer </li></ul></ul></ul><ul><ul><ul><li>and upper layers </li></ul></ul></ul>Link Network Transport Physical Upper layers
    70. 70. Summary <ul><li>Hybrid environments require revisiting protocol design decisions </li></ul>
    71. 71. Tutorials <ul><li>Visit http://www.crhc.uiuc.edu/~nhv for my tutorials on </li></ul><ul><ul><li>Mobile ad hoc networking </li></ul></ul><ul><ul><li>TCP over Wireless </li></ul></ul>
    72. 72. Thank you !! Comments/questions to [email_address] © 2001 Nitin Vaidya

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