Mobile Ad hoc Networks
3.2 Applications of Mobile Ad hoc Networks
Mobile ad hoc networks have both commercial and non-commercial applica- tions. Some examples of these are described below.
Emergency relief operations. Mobile ad hoc networks can be used for rapid deployment in rescue missions in areas where wiring is not available or
t t
3
nl re
base stations, mobile switching centers, home and visitor location registe On the other hand, mobile ad hoc networks need sophisticated distributed gorithms to perform routing and mobility management operations. Mobile hoc networks design requires making decisions on the network organisati media access protocols, network topology, bandwidth, energy requireme and routing protocols.
3.3.1 Mobile ad hoc network routing protocols
Unicasting refers to a point-to-point communication between source and I tination pairs. Multicasting refers to sending a single packet to a grou nodes which are small compared to the entire network. Due to the na of node connectivity and network resource constraints, unicast and multi routing protocols developed for the wireline networks cannot be directly plied to mobile ad hoc networks. Design of unicast routing protocols is of the main challenging topics in mobile ad hoc networks.
Several unicast routing protocols have been recently proposed for m ad hoc networks, bU;t there is no standard routing protocol available fe hoc routing, though such effort is currently under way. The existing rol protocols for mobile ad hoc networks routes are discussed in chapter 4.
proposals are discussed in chapters 5-8.
In ad hoc networks hosts may move in a group or work in a grou cessitating the need for sending multicast messages. The existing mul routing protocols for fixed networks described in [Moy94b, Dee90, I Dee96] are not suitable for mobile ad hoc networks for several reasons.
multicast servers or multicast members may move, making source-ini protocols inefficient. Second, most current protocols are based on a mul tree. A tree-based multicasting is not suitable for mobile ad hoc net1 since the multicast tree can easily get broken and transient loops IT.
formed during tree reconfiguration. Recently, some multicast protocol been proposed for mobile networks [Bom98, Lee99, Gra99, Wu98]. De ing an adaptive and reliable multicast technique for mobile ad hoc ne' still requires further investigation.
3.3.2 Mobility management
In mobile ad hoc networks there is no reference point like in cellul works. Thus, the main difference between mobility management ted developed for personal communication systems and hierarchically orl ad hoc networks are the absence of pre-established infrastructure a
inapplicability of area-based updating mobility management strategies. Mo- bility management for hierarchical organised mobile ad hoc networks is a new area that needs further investigation.
3.3.3 Medium Access Control protocols
The traditional CSMA/CD-based MAC protocols are not adequate for mobile ad hoc networks due to mobility and the wireless nature of communication.
The two main problems of wireless communication are hidden terminal and exposed terminal problems. The hidden terminal problem occurs when two nodes that cannot hear each other try to transmit to another node that can hear both of them. The exposed terminal problem occurs when two nodes that can hear each other transmit to another node that can hear only one of them. A mobile ad hoc network requires the design of an appropriate medium access control protocol to reduce or avoid these problems.
Since the CSMA/CD protocol does not function well in a mobile network environment, the IEEE S02.11 Wireless LAN standard [IEE97] that uses Carrier Sense Multiple Access for Collision Avoidance (CSMA/CA) protocol has been proposed for mobile networks. Other protocols that attempt to overcome the shortcomings of CSMAjCD are discussed in [Bah94, Fu197, Jin9S, Kar90, Lin97].
Most of these protocols are designed for infrastructure-based mobile net- works and they assume that the interfering nodes can hear Request To Send/
Clear To Send (RTSjCTS) dialogs, but this assumption is not valid in a highly mobile network environment. A new media access control protocol called Dual Busy Tone Multiple Access [DBTMA] [Jin9S] has recently been proposed for mobile ad hoc networks. In this protocol, a single common chan- nel is split into two sub-channels. The first is a data channel which is used to transmit data packets. The second is a control channel which is used to transmit control packets such as RTS and CTS. Two busy tones are assigned to the control channel: the receive busy tone and the transmit busy tone.
The protocol improves channel capacity while avoiding most of the collisions that occur due to hidden terminal problem. Efficient medium access control protocols that avoid collisions and also solve the fairness problem are needed for mobile ad hoc networks.
3.3.4 Data management
Data management includes operations such as data dissemination over wire- less link, location-dependent querying of data, transaction management, in- formation retrieval and advanced interfaces for mobile computers. Data management in cellular networks is based on asymmetric data transmission.
Since packet receiving consumes less power than transmitting and mobile nodes have scarce resources, data is sent to a mobile node with periodic packet broadcasts made from the fixed networks [Imi94]. Such transmission mechanism leads to communication latency. A joint broadcasting scheduling approach has recently been proposed in [Su98] where the server broadcasts the information and the user caches such information. In mobile ad hoc networks, data management poses a new challenge. Each mobile node is re- sponsible for maintaining a database for user data and control information.