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Medium Access Control with Directional Antennas 213 physical and virtual carrier sensing as in DMAC. After the CTS is received by A, it proceeds to send the DATA packet directionally and this is followed by a directional ACK from node E to node A. Nodes that overhear either the CTS or the DATA messages update their DNAVs accordingly. The authors in [6] perform extensive simulations to study the performance of DMAC and MMAC. They find that in topologies where nodes are aligned (either string topologies wherein nodes are arranged along a line or in grid topologies) the benefits of using the directional antennas are dwindled due to the problems of deafness and asymmetry described earlier. The benefits were more pronounced when random topologies were considered. One of the limitations of this work was that the authors assume that a node is aware of its neighborhood and somehow has the routing information required to send out the multi-hop RTS messages. Furthermore, the protocols are vulnerable to deafness and do not study neighbor discovery and the tracking of neighbors in mobile scenarios. 7.3.7 Dealing with Deafness: The Circular RTS message In [21], the authors propose the use of the circular RTS message to deal with many of the problems reported in [6]. Omni-directional transmission and reception of the RTS messages could result in directional neighbors not knowing about the forthcoming communication since the OOR is potentially much smaller than than DOR. However, simply using a directional RTS could potentially result in the hidden terminal and deafness problems reported in [6]. Korakis, Jakllari and Tassiulas propose that instead of transmitting the directional RTS in simply the direction of the intended neighbor the RTS be now transmitted in all possible directions. To illustrate this we refer to Figure 7.7. Note in the figure that by circularly transmitting the RTS message in each of the M possible directions, a node can potentially inform all of its DO neighbors of its intended transmission. The source also indicates the antenna beam (switched beam antennas are assumed) on which the intended transmission is to take place. Accordingly, nodes can (a) set their DNAV vectors appropriately (b) recognize that the node is in the process of communication and avoid the problems due to deafness. Each node is required to maintain a location table where it records the information with regards to the communications in progress and the directions in which these communications are being carried out. When transmitting the circular RTS message a node has to take care not to transmit the message in those directions where it is prohibited from doing so (due to either physical or virtual carrier sensing). Thus, the circular RTS message cannot completely eliminate the problems due to hidden terminals and deafness. The authors perform extensive simulations to show that in spite
214 Use of Smart Antennas in Ad Hoc Networks Figure 7.7. The Circular RTS message of this, in typical scenarios, the circular RTS message helps alleviate these problems to a large extent. The unfairness in access seen with DMAC is also reduced to a large extent. The circular RTS is also extremely useful in tracking neighbors in mobile conditions. Since the node transmits the RTS message in all possible directions, even if a neighbor has moved, it can still possibly hear the RTS message and respond with a CTS message. Thus, the new proposed medium access control scheme is robust under mobility to a large extent. One of pitfalls of using the circular RTS message is that there is an additional latency incurred with every transmission. If a neighbor were to successfully transmit an RTS message in all of the M possible directions (Figure 7.7), the time required is M times that required for a single RTS transmission. Furthermore, this scheme generates a significant amount of overhead by transmitting these multiple directional RTS messages. In spite of these limitations the use of the circular RTS is the only proposed scheme to date that reduces the effects of hidden terminals and deafness with directional antennas. 7.3.8 Other Collision Avoidance MAC Protocols There are other MAC protocols designed for use with directional antennas [3], [19], [20]. The protocols are similar to the ones described. The key ideas are based on nodes identifying the directions in which there are ongoing communications and supressing transmissions in those directions until the present communications are completed. While [3] suggests marking the antenna sector on which the transmission was received (sectorized antennas are assumed)
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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
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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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Communication-Time Energy Conservat
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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
Page 216 and 217: Conclusion 191 [6] [7] [8] [9] [10]
Page 218 and 219: Conclusion 193 [33] [34] [35] [36]
Page 220 and 221: Conclusion 195 [59] [60] [61] [62]
Page 222 and 223: Chapter 7 USE OF SMART ANTENNAS IN
Page 224 and 225: Smart Antenna Basics and Models 199
Page 226 and 227: Medium Access Control with Directio
Page 242 and 243: Routing with Directional Antennas 2
Page 248 and 249: Broadcast with Directional Antennas
Page 250 and 251: Broadcast with Directional Antennas
Page 252 and 253: Summary 227 [4] [5] [6] [7] [8] [9]
Page 254 and 255: Chapter 8 QOS ISSUES IN AD-HOC NETW
Page 256 and 257: Introduction 231 The concept of ad-
Page 258 and 259: Physical Layer 233 The 802.11a stan
Page 260 and 261: Medium Access Layer 235 neighbors,
Page 262 and 263: Medium Access Layer 237 Figure 8.5.
Page 264 and 265: QoS Routing 239 where is the number
Page 266 and 267: QoS at other Networking Layers 241
Page 268 and 269: Inter-Layer Design Approaches 243 8
Page 270 and 271: Conclusion 245 are specifically des
Page 272 and 273: Conclusion 247 [13] S. Mangold, S.
Page 274 and 275: Chapter 9 SECURITY IN MOBILE AD-HOC
Page 276 and 277: Potential Attacks 251 attacks, such
Page 278 and 279: Attack Prevention Techniques 253 9.
Page 280 and 281: Intrusion Detection Techniques 255
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Intrusion Detection Techniques 263
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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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