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Wireless Ad-hoc Networks

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Thejas Kesari

on 8 February 2015

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Transcript of Wireless Ad-hoc Networks

IEEE 802.11 belongs to unlicensed ISM band - free to use
Nodes in the ad-hoc network are not fixed.
Wireless networks are used to interconnect several devices and relay communication between them in an easy, energy efficient and reliable manner.
The ability to interconnect several devices without existing infrastructure gives wireless networks an edge over the wired networks.
Wireless ad-hoc networks
Decentralized - does not rely on a pre existing infrastructure such as routers or access points.
Ad hoc is a Latin phrase meaning "for this"
It refers to something that is created for special needs, tailor-made, or handcrafted.
Scalable Wireless Ad-hoc Network (SWAN)
Ajaya H S
Eshwar Gowda M N
Nitish S Prabhu
Thejas N Kesari

Mr. V Nutan Prasad
Ad-hoc networks
Issues in MANET
Routing Protocols
Key References

Each node participates in routing by forwarding data for other nodes, so the determination of which nodes forward data is made dynamically on the basis of network connectivity.
Annual expenditure on cellphone bills in USD
Expenses of an average Indian youth
*Forbes 2012
*Forbes 2012
Wi-Fi is extremely popular and almost universally compatible.
A standard Wi-Fi device can work anywhere in the world.
Mobile Ad-hoc Networks
It was initially conceptualized and used in military applications wherein communication in the field of combat is of utmost prominence
They play a major role in enabling quick and effortless communication in places where network infrastructure is not prevalent or is difficult to establish.
Issues in MANET
They are infrastructureless
Mobile ad hoc networks rely on multi hopping. The lack of a fixed dedicated infrastructure poses a lot more design issues than in fixed networks.
In a fixed network, a certain topology like ring, bus, mesh, etc., is taken as standard and the routing is done accordingly. Whereas here, since nodes can move arbitrarily and unpredictably, it results in route changes dynamically which may cause network partitions and in turn packet losses.
They involve dynamically changing network topologies
As much as this is an advantage, the lack of a centralized entity or a server poses its own challenges.
This effectively means that the responsibility of network management has to be distributed among many different nodes, which in turn causes difficulty in error detection and correction.
The radio interface at each node uses broadcasting for transmitting traffic and usually has limited wireless transmission range, resulting in specific mobile ad hoc network problems like hidden terminal problems, exposed terminal problem, and so on. Collisions are inherent to the medium, and there is a higher probability of packet losses due to transmission errors compared to wireline systems.
Range issues
Lack of a centralized entity
Because mobile nodes communicate with each other via bandwidth-constrained, variable capacity, error-prone, and insecure wireless channels, wireless links will continue to have significantly lower capacity than wired links and, hence, congestion is more problematic.

Limited Link Bandwidth
Routing Protocols
Based on link state algorithm
Network divided based on scope
Single hop - higher frequency, multiple hop - lower frequency
Local information - highest accuracy
Fisheye State Routing
Based on link state algorithm
Conventional link state approach is not suitable for mobile ad hoc networks because the network structure is continuously changing due to which the update overhead is very high.
Selected nodes are called as Multipoint Relay (MPR) nodes, and technique is called Multipoint Relaying. MPR nodes are nodes at single hop distance such that they cover all second hop nodes for the given node.
All other nodes that are not MPRs can only access the routing information from the MPRs but cannot transmit it.
Optimized Link State Routing Protocol
Topology Broadcast based on Reverse Path Forwarding
Link state based protocol
Forwards the routing information based the concept of Reverse Path Forwarding (RPF)
Each TBRPF node maintains a partial topology of the network in its routing table in form of a minimum-hop-tree
A routing protocol specifies the way in which nodes in a network must communicate in order to disseminate specific information to a particular destination in the network.
The routing protocols consists of inherent information that enables routers in the network to select routes between any two nodes in a computer network.
Routing Protocols
Flat routing
Hierarchical Routing
Geographic Position-based Routing
Dynamic Source Routing (DSR)
On-demand protocol where connections are made only if and when required

Basic approach: Request - Discovery - Construction
Ad-hoc On-demand Distance Vector Protocol (AODV)
Mostly similar to DSR, except for the fact that it stores information about only the next hop - hence, highly scalable due to very less overhead
Destination Sequence Number (DSN)
RouteRequest Packets - RouteReply Packets
Zone Routing Protocol (ZRP)
It combines the best features of proactive and reactive routing in a hierarchical manner
For every node, two zones are declared namely the Proactive zone and the Reactive zone.
Nodes for which the connectivity is maintained in the routing table, i.e., nodes that are accessible with lesser number of hops are placed in the proactive zone. Nodes which require more number of hops are placed in the reactive zone.
It uses specific geographic information to specify the destination, rather than logical node address
A special computer host is in charge of receiving and sending geographic messages (GeoHost)
Location Aided Routing (LAR)
Utilizes location information to limit the area for discovering a new route to a smaller requested zone
Performs route discovery through limited flooding

Key Applications
Wireless Data Networks
Sensor Networks
Distributed Control Systems
Automated Highway
Current Technology
UAV Swarm Co-ordination
Military Sensor Networks
Smart homes
Current popular network management algorithms were mostly designed to work on fixed or relatively small wireless networks.
Many mobile ad hoc network applications involve large networks with tens of thousands of nodes, as found, for example, in sensor networks and tactical networks. Scalability is critical to the successful deployment of such networks.
Network Scalability
Key References
"Mobile Ad hoc Networking", Stefano Basagni, et al., Wiley Publication
"Ad-Hoc Wireless Networks: Architectures and Protocols", C Siva Ram Murthy, et al., Prentice Hall, 2004
"A review of routing protocols for mobile ad hoc networks", Mehran Abolhasan, et al., Ad Hoc Networks, Elsevier, June 2003
"Scalable Routing Protocols for Mobile Ad Hoc Networks", Xiaoyan Hong, et al., IEEE Trans.
"Wireless Sensor Networks", F. L. Lewis, Smart Environments: Technologies, Protocols, and Applications John Wiley, New York, 2004.
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