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TCP-aware Cross-layered Solutions 141 following three goals: (i) To minimize the probability of route failures; (ii) To predict route failures in advance and thus enable the source to recompute an alternate route before the existing route fails; and (iii) To minimize the latency in conveying route failure information to the source, for route failures that are not successfully predicted. The Atra framework consists of three mechanisms targeted toward each of the above goals respectively: Mechanisms The key mechanisms in Atra are the following: Symmetric Route Pinning: The DSR routing protocol does not explicitly use symmetric routes between a source and a destination, i.e. the route taken from the source to the destination can be different from the route taken from the destination to the source. While the use of asymmetric routes is not an issue in a static network, in a dynamic network where nodes are mobile using an asymmetric path, increases the probability of route failure for a connection. Specifically, a TCP connection will stall irrespective of whether the forward path is broken or the reverse path is broken. Taking the simple scenario of using two edge-disjoint routes for the data and the ACK paths with hop lengths of and respectively, and assuming a uniform probability of link failure for all links in the network (which is not unrealistic given the use of the random way-point mobility model), the probability of a path failure is Hence, in the first mechanism within the Atra framework called symmetric route pinning (SRP), the ACK path of a TCP connection is always kept the same as the data path in order to reduce the probability of route failures. The mechanism implemented at the DSR layer does the route pinning only for uni-directional communication. The reasoning is as follows: while it is true that the forward path progression can be asynchronous to the reverse path progression, performing route pinning to piggybacked ACKs in bi-directional communication can severely increase the congestion along the path whereas in the case of asymmetric paths, implicit load balancing is performed. Route Failure Prediction: The symmetric route pinning mechanism merely reduces the probability of route failures for a connection. Hence, the second mechanism in Atra attempts to predict the occurrence of a link failure by monitoring the signal strength of the packets received from the corresponding neighbor. Based on the progression of signal strengths of packet receptions from
142 Transport Layer Protocols in Ad Hoc Networks a particular neighbor, a node predicts the occurrence of the link failure. Maintaining a history of the progression enables nodes to dynamically profile the speed at which the the two nodes are moving away from each other by merely observing the slope of the progression. The threshold to trigger a prediction is a tunable parameter that would determine the look-ahead time for the link failure. The objective is to enable the completion of an alternate route computation before the failure of the current path. A critical aspect of the prediction process is the propagation model used. Since the two-ray ground reflection model is assumed for distances greater than 100m, the corresponding equation is used to calculate the threshold receive power corresponding to a particular slope (and hence speed) and look-ahead time. Based on the model, the received power can be specified as: where K is a constant and is a function of the receive and transmitter antenna gains and heights, and the transmit power. is the distance between the transmitter and the receiver. Thus given a look-ahead time and the observed relative speed between the two nodes the threshold power to trigger a prediction can be calculated as: where is the transmission range. The speed is computed from the slope of the history of transmission powers observed. If the size of the history is N (N packet reception powers and corresponding times), the speed is calculated as follows: where and represent the received power and time of reception for the packet in the history. When a source receives a predicted route failure message it issues a new route request, but continues to use the current path either till the new route is computed or the current route fails and it receives a normal route error. Route requests are suppressed based on the same thresholds used to predict route failures. Hence, a route that is close to failure will not be chosen during any route computation process. In essence, the mechanism tries to predict link failures in advance and proactively determine an alternate route before the failure of the route
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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
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List of Figures 1.1 Internet in the
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List of Figures xiii 6.3 COMPOW com
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List of Figures xv 9.1 9.2 An IDS a
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List of Tables 2.1 2.2 2.3 2.4 2.5
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Contributing Authors Samir R. Das i
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Preface Wireless mobile networks an
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Acknowledgments xxiii We wish to ex
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Chapter 1 AD HOC NETWORKS Emerging
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Introduction and Definitions 3 coul
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Introduction and Definitions 5 Secu
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Ad Hoc Network Applications 7 tunis
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Ad Hoc Network Applications 9 The d
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Ad Hoc Network Applications 11 Figu
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Design Challenges 13 example of cro
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Evaluating Ad Hoc Network Protocols
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Overview of the Chapters in this Bo
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Overview of the Chapters in this Bo
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Conclusions 21 1.6 Conclusions This
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Chapter 2 COLLISION AVOIDANCE PROTO
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Performance of collision avoidance
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Framework and Mechanisms for Fair A
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Conclusion 59 In the first part of
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Conclusion 61 [13] [14] [15] [16] [
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Chapter 3 ROUTING IN MOBILE AD HOC
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Flooding 65 vector and link state p
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Flooding 67 centralized approximati
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Proactive Routing 69 status of each
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Proactive Routing 71 Topology Broad
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On-demand Routing 73 reply packets
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On-demand Routing 75 during the lin
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Proactive Versus On-demand Debate 7
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Proactive Versus On-demand Debate 7
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Location-based Routing 81 to find a
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Location-based Routing 83 Figure 3.
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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
Page 116 and 117: Chapter 4 MULTICASTING IN AD HOC NE
Page 118 and 119: Introduction 93 The mobility of the
Page 120 and 121: Classifications of Protocols 95 red
Page 122 and 123: Multicasting Protocols 97 this sect
Page 124 and 125: Multicasting Protocols 99 as close
Page 126 and 127: Multicasting Protocols 101 In ODMRP
Page 128 and 129: Multicasting Protocols 103 hoc netw
Page 130 and 131: Multicasting Protocols 105 A member
Page 132 and 133: Multicasting Protocols 107 Figure 4
Page 134 and 135: Broadcasting 109 “talk” to a ra
Page 136 and 137: Broadcasting 111 broadcasted packet
Page 138 and 139: Protocol Comparisons 113 are cluste
Page 140 and 141: Overarching Issues 115 is user data
Page 142 and 143: Overarching Issues 117 and RTS/CTS
Page 144 and 145: Conclusions and Future Directions 1
Page 146 and 147: Conclusions and Future Directions 1
Page 148 and 149: Chapter 5 TRANSPORT LAYER PROTOCOLS
Page 150 and 151: TCP and Ad-hoc Networks 125 Modifie
Page 152 and 153: TCP and Ad-hoc Networks 127 mechani
Page 154 and 155: TCP and Ad-hoc Networks 129 timeout
Page 156 and 157: TCP and Ad-hoc Networks 131 to freq
Page 158 and 159: TCP and Ad-hoc Networks 133 Figure
Page 160 and 161: Transport Layer for Ad-hoc Networks
Page 162 and 163: Modified TCP 137 MAC layers without
Page 164 and 165: Modified TCP 139 Figure 5.6. TCP-EL
Page 168 and 169: TCP-aware Cross-layered Solutions 1
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Page 172 and 173: Ad-hoc Transport Protocol 147 in it
Page 174 and 175: Ad-hoc Transport Protocol Figure 5.
Page 176 and 177: Summary 151 References [1] [2] [3]
Page 178 and 179: Chapter 6 ENERGY CONSERVATION Robin
Page 180 and 181: Energy Consumption in Ad Hoc Networ
Page 182 and 183: Energy Consumption in Ad Hoc Networ
Page 184 and 185: Communication-Time Energy Conservat
Page 200 and 201: Idle-time Energy Conservation 175 a
Page 202 and 203: Idle-time Energy Conservation 177 T
Page 204 and 205: Idle-time Energy Conservation 179 k
Page 206 and 207: Idle-time Energy Conservation 181 F
Page 210 and 211: Idle-time Energy Conservation 185 t
Page 212 and 213: 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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