Ad Hoc Networks : Technologies and Protocols - University of ...

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Performance of collision avoidance protocols 37 Figure 2.5. Throughput comparison Figure 2.5 compares the throughput of collision avoidance against that of CSMA with different values of N and data packet lengths‚ and we can make the following observations from the above results. When data packet is long‚ the throughput of CSMA is very low‚ even for the case in which only N = 3 nodes are competing for the shared channel. By comparison‚ the RTS/CTS scheme can achieve much higher throughput‚ even
38 Collision Avoidance Protocols when the average number of competing nodes is 10. The reason is simple‚ the larger a data packet is‚ the worse the impact of hidden terminals is for that packet in CSMA‚ because the vulnerability period becomes twice the length of the data packet. With collision avoidance‚ the vulnerability period of a handshake is independent of the length of data packets‚ and in the worse case‚ equals twice the length of an RTS. When a data packet is not very long and the overhead of the collision avoidance and handshake seems to be rather high‚ collision avoidance can still achieve marginally better throughput than CSMA. We need to emphasize that the performance of the actual CSMA protocol would be much worse than the idealized model we have used for comparison purposes‚ because of the effect of acknowledgments. Despite the advantage of collision avoidance‚ its throughput still degrades rapidly with the increase of N. This is also evident for low values of as shown in Figure 2.5. This is due the fact that nodes are spending much more time on collision avoidance and backoff. When N increases‚ decreases much slower to achieve optimum throughput‚ which already decreases. This shows that collision avoidance becomes more and more ineffective when the number of competing nodes within a region increases‚ even though these nodes are quite “polite” in their access to the shared channel. This is also different from a fullyconnected network‚ in which the maximum throughput is largely indifferent to the number of nodes within a region [11]. Our results also reveal that hidden terminals degrade the performance of collision avoidance protocols beyond the basic effect of having a longer vulnerability period for RTSs. There is one dilemma here. On the one hand‚ it is very difficult to get all the competing nodes around one node coordinated well by probabilistic methods such as randomized backoff. Here the competing nodes refer to both one-hop and two-hop neighbors 2 of the node. In actual MAC protocols‚ the collisions of data packets may still occur and throughput degrades with increasing numbers of neighbors. On the other hand‚ even if all the competing nodes of one node defer their access for the node‚ the possible spatial reuse in multi-hop networks is greatly reduced and hence the maximum achievable throughput is reduced. This dilemma leads to the scalability problem of contention-based MAC protocols that occurs much earlier than people might expect‚ as the throughput is already quite meager when the average of competing nodes within a region (N) is only ten. 2 Here we refer to those nodes that have at least one common neighbor with a node but are not direct neighbors of the node as the node’s two-hop neighbors.
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AD HOC NETWORKS Technologies and Pr
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AD HOC NETWORKS Technologies and Pr
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Contents List of Figures List of Ta
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Contents vii 4.7. Conclusions and F
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Contents ix 9.2. Potential Attacks
Page 12 and 13: List of Figures 1.1 Internet in the
Page 14 and 15: List of Figures xiii 6.3 COMPOW com
Page 16 and 17: List of Figures xv 9.1 9.2 An IDS a
Page 18 and 19: List of Tables 2.1 2.2 2.3 2.4 2.5
Page 20 and 21: Contributing Authors Samir R. Das i
Page 22 and 23: Preface Wireless mobile networks an
Page 24 and 25: Acknowledgments xxiii We wish to ex
Page 26 and 27: Chapter 1 AD HOC NETWORKS Emerging
Page 28 and 29: Introduction and Definitions 3 coul
Page 30 and 31: Introduction and Definitions 5 Secu
Page 32 and 33: Ad Hoc Network Applications 7 tunis
Page 34 and 35: Ad Hoc Network Applications 9 The d
Page 36 and 37: Ad Hoc Network Applications 11 Figu
Page 38 and 39: Design Challenges 13 example of cro
Page 40 and 41: Evaluating Ad Hoc Network Protocols
Page 42 and 43: Overview of the Chapters in this Bo
Page 44 and 45: Overview of the Chapters in this Bo
Page 46 and 47: Conclusions 21 1.6 Conclusions This
Page 48 and 49: Chapter 2 COLLISION AVOIDANCE PROTO
Page 50 and 51: Performance of collision avoidance
Page 70 and 71: Framework and Mechanisms for Fair A
Page 84 and 85: Conclusion 59 In the first part of
Page 86 and 87: Conclusion 61 [13] [14] [15] [16] [
Page 88 and 89: Chapter 3 ROUTING IN MOBILE AD HOC
Page 90 and 91: Flooding 65 vector and link state p
Page 92 and 93: Flooding 67 centralized approximati
Page 94 and 95: Proactive Routing 69 status of each
Page 96 and 97: Proactive Routing 71 Topology Broad
Page 98 and 99: On-demand Routing 73 reply packets
Page 100 and 101: On-demand Routing 75 during the lin
Page 102 and 103: Proactive Versus On-demand Debate 7
Page 104 and 105: Proactive Versus On-demand Debate 7
Page 106 and 107: Location-based Routing 81 to find a
Page 108 and 109: Location-based Routing 83 Figure 3.
Page 110 and 111: Concluding Remarks 85 relative meri
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Concluding Remarks 87 [14] [15] [16
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Concluding Remarks 89 [42] [43] [44
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Chapter 4 MULTICASTING IN AD HOC NE
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Introduction 93 The mobility of the
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Classifications of Protocols 95 red
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Multicasting Protocols 97 this sect
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Multicasting Protocols 99 as close
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Multicasting Protocols 101 In ODMRP
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Multicasting Protocols 103 hoc netw
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Multicasting Protocols 105 A member
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Multicasting Protocols 107 Figure 4
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Broadcasting 109 “talk” to a ra
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Broadcasting 111 broadcasted packet
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Protocol Comparisons 113 are cluste
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Overarching Issues 115 is user data
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Overarching Issues 117 and RTS/CTS
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Conclusions and Future Directions 1
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Conclusions and Future Directions 1
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Chapter 5 TRANSPORT LAYER PROTOCOLS
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TCP and Ad-hoc Networks 125 Modifie
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TCP and Ad-hoc Networks 127 mechani
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TCP and Ad-hoc Networks 129 timeout
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TCP and Ad-hoc Networks 131 to freq
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TCP and Ad-hoc Networks 133 Figure
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Transport Layer for Ad-hoc Networks
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Modified TCP 137 MAC layers without
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Modified TCP 139 Figure 5.6. TCP-EL
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TCP-aware Cross-layered Solutions 1
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Ad-hoc Transport Protocol 147 in it
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Ad-hoc Transport Protocol Figure 5.
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Summary 151 References [1] [2] [3]
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Chapter 6 ENERGY CONSERVATION Robin
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Energy Consumption in Ad Hoc Networ
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Energy Consumption in Ad Hoc Networ
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Communication-Time Energy Conservat
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Idle-time Energy Conservation 175 a
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Idle-time Energy Conservation 177 T
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Idle-time Energy Conservation 179 k
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Idle-time Energy Conservation 181 F
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Idle-time Energy Conservation 185 t
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Idle-time Energy Conservation 187 c
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Conclusion 191 [6] [7] [8] [9] [10]
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Conclusion 193 [33] [34] [35] [36]
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Conclusion 195 [59] [60] [61] [62]
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Chapter 7 USE OF SMART ANTENNAS IN
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Smart Antenna Basics and Models 199
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Medium Access Control with Directio
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Routing with Directional Antennas 2
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Broadcast with Directional Antennas
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Broadcast with Directional Antennas
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Summary 227 [4] [5] [6] [7] [8] [9]
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Chapter 8 QOS ISSUES IN AD-HOC NETW
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Introduction 231 The concept of ad-
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Physical Layer 233 The 802.11a stan
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Medium Access Layer 235 neighbors,
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Medium Access Layer 237 Figure 8.5.
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QoS Routing 239 where is the number
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QoS at other Networking Layers 241
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Inter-Layer Design Approaches 243 8
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Conclusion 245 are specifically des
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Conclusion 247 [13] S. Mangold, S.
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Chapter 9 SECURITY IN MOBILE AD-HOC
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Potential Attacks 251 attacks, such
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Attack Prevention Techniques 253 9.
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Intrusion Detection Techniques 255
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Conclusion 265 an important and sti
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Conclusion 267 [24] [25] [26] [27]
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Index Ad hoc network multicast rout
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