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

More documents

Recommendations

Info

Medium Access Control with Directional Antennas 207 for the duration indicated in the message. The reason that this was deemed appropriate was that the nodes simply performed omni-directional receptions. However, if directional receptions were possible, one could potentially examine directional channel availability. Thus, a node, upon the receipt of an RTS or a CTS message, precludes transmissions only in those directions in which it interferes with the communications related to the received RTS or CTS message. The mechanisms proposed in [14], like in other work discussed earlier, are extensions to the IEEE 802.11 MAC protocol to enable its use in the presence of directional antennas. In the following paragraphs, we discuss these mechanisms in brief. First, for directional virtual carrier sensing to work, each node would need to cache estimated angles of arrival (AOAs) from neighboring nodes whenever it hears any signal from these nodes. This is done regardless of whether the communication was intended for the node under discussion. The AOA is an indicator of where the node is located. Thus, when a node wishes to communicate with a particular neighbor, it uses the cached AOA information with regards to that neighbor and sends a directional RTS message in the the direction of the neighbor. Additional attempts are made if the node fails to receive a CTS response from the neighbor. If the node does not get a CTS response after 4 directional RTS attempts, it resorts to omni-directional transmissions of the RTS message. The cached AOA information is purged after the failure of the directional RTS attempts. In order to comply with the IEEE 802.11 standard where the total number of RTS attempts for a particular packet are limited to seven, the node will make three omni-directional attempts before it drops the packet and reports a link failure to the higher layers. The authors in [14] assume that a steerable beam antenna is used. Upon the receipt of an RTS message, the receiver is assumed to lock the receive beam pattern for maximizing the received power. Similarly, the orignal transmitter does the same upon the receipt of the CTS message from the receiver. The beam patterns are then used both for transmission and reception. Upon the completion of the communication (through the transmission of the ACK message) the beam patterns are unlocked. The locking prevents the nodes from listening to other transmissions for the duration of the communication. Finally, each node that overhears a control message exchange, uses a directional network allocation vector (DNAV) as opposed to the network allocation vector (NAV) used in the original IEEE 802.11 MAC protocol. The DNAV allows a node to specify each direction (the direction of the main lobe of the communication as determined from the control message) and the angular beamwidth in each particular direction that is to be avoided so as to remove conflicts with ongoing communications. When a node wishes to initiate a new transmission (or respond to a new request for communications) it checks its DNAV to see if the particular requested direction is open and transmits in the
208 Use of Smart Antennas in Ad Hoc Networks direction only if it is. The width of DNAV is dictated by the beamwidth scoped by the underlying directional antenna. If this beamwidth can be dynamically changed, the DNAV would take this into account. The performance studies in [14] show that the use of DVCS can provide up to a threefold or fourfold increase in network capacity (measured in terms of throughput) as compared to the IEEE 802.11 protocol used with omnidirectional antennas. They also do additional simulation experiments to study the behavior of the scheme in the presence of some nodes that are simply capable of omni-directional transmissions and they find that there is still a benefit in using DVCS (only nodes equipped with directional antennas use DVCS). 7.3.5 The impact of increased directional range The work in [14] assumes that the directional range is equal to the omnidirectional range. However, as mentioned earlier, in reality, the directional range might be much higher than the omni-directional range. This is actually beneficial since network partitions that may actually occur with the use of omni-directional antennas could be potentially bridged by the use of directional antennas. Furthermore, since the range is longer, one can now potentially compute shorter routes which can lead to improved efficiency. However, the medium access control protocol discussed earlier has certain problems when an extended directional range is considered. In [6], Roy Choudhury, Yang, Ramanathan and Vaidya look at these problems in depth. They call the basic medium access control protocol the Directional MAC or DMAC protocol; the protocol is similar to the protocol described in [14]. The protocol assumes that nodes are aware of the locations of their neighbors. When idle they listen in the omni-directional mode. However, when a node intends to transmit a message it transmits a directional RTS message towards the intended neighbor. A directional CTS is sent in response. Both directional transmissions and directional receptions are employed for the exchange of the DATA and the ACK messages. Overhearing nodes update their directional network allocation vectors as in the protocol in [14]. The basic DMAC suffers from a number of problems due to the directional nature of the communications and the increased directional range. Note here that if the gain of the omni-directional antenna is and the gain of the directional antenna for a given beamwidth is then Furthermore, if one were to deploy directional transmissions but omni-directional receptions, the total gain seen is On the other hand, if one were to deploy both directional transmissions and directional receptions the gain observed would be In order to understand the problems, we consider the scenario shown in Figure 7.5. The scenario is similar to the one considered in [6]. First we
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 50 and 51:
Performance of collision avoidance
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Page 60 and 61:
Page 62 and 63:
Page 64 and 65:
Page 66 and 67:
Page 68 and 69:
Page 70 and 71:
Framework and Mechanisms for Fair A
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
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
Page 112 and 113:
Concluding Remarks 87 [14] [15] [16
Page 114 and 115:
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 166 and 167:
TCP-aware Cross-layered Solutions 1
Page 168 and 169:
Page 170 and 171:
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
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
Page 282 and 283:
Intrusion Detection Techniques 257
Page 284 and 285:
Page 286 and 287:
Page 288 and 289:
Page 290 and 291:
Conclusion 265 an important and sti
Page 292 and 293:
Conclusion 267 [24] [25] [26] [27]
Page 294 and 295:
Index Ad hoc network multicast rout
show all

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

Create successful ePaper yourself

Delete template?

Save as template?