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Performance of collision avoidance protocols 25 2.1 Performance of collision avoidance protocols In Section 2.1.1, we present the analysis of the sender-initiated collisionavoidance scheme based on a four-way handshake and non-persistent carrier sensing, which can be also called the RTS/CTS-based scheme for the sake of simplicity. We first adopt a simple model in which nodes are randomly placed on a plane according to two-dimensional Poisson distribution with density Varying has the effect of changing the congestion level within a region as well as the number of hidden terminals. In this model, it is also assumed that each node is ready to transmit independently in each time slot with probability where is a protocol-dependent parameter. This model was first used by Takagi and Kleinrock [8] to derive the optimum transmission range of a node in a multi-hop wireless network, and was used subsequently by Wu and Varshney [9] to derive the throughputs of non-persistent CSMA and some variants of busy tone multiple access (BTMA) protocols [6]. Then we assume that both carrier sensing and collision avoidance work perfectly, that is, that nodes can accurately sense the channel busy or idle, and that the RTS/CTS scheme can avoid the transmission of data packets that collide with other packets at the receivers. The latter assumption can be called perfect collision avoidance and has been shown to be doable in the floor acquisition multiple access (FAMA) protocol [3]. Later we extend this model to take into account the possibility of data packets colliding with other transmissions, so that the model is also applicable to other MAC protocols, such as the popular IEEE 802.11 protocol, in which perfect collision avoidance is not strictly enforced. In Section 2.1.2, we present numerical results from our analysis. We compare the performance of the sender-initiated collision avoidance scheme against the idealized non-persistent CSMA protocol in which a secondary channel is assumed to send acknowledgments in zero time and without collisions [6, 9], as the latter is the only protocol whose analysis for multi-hop ad hoc networks is available for comparison to date. It is shown that the RTS/CTS scheme can achieve far better throughput than the CSMA protocol, even when the overhead due to RTS/CTS exchange is high. The results illustrate the importance of enforcing collision avoidance in the RTS/CTS handshake. However, the analytical results also indicate that the aggregate throughput of sender-initiated collision avoidance drops faster than that in a fully-connected network when the number of competing nodes within a region increases. This contrasts with conclusions drawn from the analysis of collision avoidance in fully-connected networks or networks with limited hidden terminals [3]. Our results show that hidden terminals degrade the performance of collision avoidance protocols beyond the basic effect of having a longer vulnerability period for RTSs. Hence, it follows that collision avoidance becomes more and more ineffective for a relatively crowded region with hidden terminals.
26 Collision Avoidance Protocols To validate the findings drawn from this analysis, in Section 2.1.3 we present simulations of the popular IEEE 802.11 MAC protocol. The simulation results clearly show that the IEEE 802.11 MAC protocol cannot ensure collision-free transmission of data packets, and that almost half of the data packets transmitted cannot be acknowledged due to collisions, even when the number of competing nodes in a neighborhood is only eight! However, the performance of the simulated IEEE 802.11 MAC protocol correlates well with what is predicted in the extended analysis, which takes into account the effect of data packet collisions and is used for the case when the number of competing nodes in a region is small. When the number of competing nodes in a region increases, the performance gap between IEEE 802.11 and the analysis decreases, which validates the statement that even a perfect collision-avoidance protocol loses its effectiveness gradually due to the random nature of the channel access and the limited information available to competing nodes. The simulation results for the IEEE 802.11 protocol also show a larger variation in throughput than the predicted performance from the analytical model, which is due to its inherent fairness problems which motivates the second part of the work reported in this chapter. 2.1.1 Approximate Analysis In this section, we derive the approximate throughput of a perfect collision avoidance protocol. In our network model, nodes are two-dimensionally Poisson distributed over a plane with density i.e., the probability of finding nodes in an area of S is given by: Assume that each node has the same transmission and receiving range of R, and denote by N the average number of nodes within a circular region of radius R; therefore, we have To simplify our analysis, we assume that nodes operate in time-slotted mode. As prior results for CSMA and collision-avoidance protocols show [6], the performance of MAC protocols based on carrier sensing is much the same as the performance of their time-slotted counterparts in which the length of a time slot equals one propagation delay and the propagation delay is much smaller than the transmission time of data packets. The length of each time slot is denoted by Note that is not just the propagation delay, because it also includes the overhead due to the transmit-toreceive turn-around time, carrier sensing delay and processing time. In effect, represents the time required for all the nodes within the transmission range of a node to know the event that occurred seconds ago. The transmission times of RTS, CTS, data, and ACK packets are normalized with regard to and are
Page 2 and 3: AD HOC NETWORKS Technologies and Pr
Page 4 and 5: AD HOC NETWORKS Technologies and Pr
Page 6 and 7: Contents List of Figures List of Ta
Page 8 and 9: Contents vii 4.7. Conclusions and F
Page 10 and 11: 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 52 and 53: 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
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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
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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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