ROUTING ALGORITHMS IN AD HOC NETWORKS Presented by Vishwanee Raghoonundun Assisted by Maheshwarnath Behary & Y. Koteswara MSc Computer Networks Middlesex University

Introduction Definition of Ad hoc networks Routing in Ad hoc networks Ad Hoc Routing Algorithms Source Routing Distributed Routing Hierarchical Routing Conclusion Reference

1. Definition of Ad hoc network A mobile ad hoc network (MANET) is a collection of two or more nodes wirelessly connected together into a network. It is said to be infrastructureless as it does not have any central node, wires or fized base stations. A Manet is also referred to as multi-hop connection and is suitable for application areas such as: battlefield communications disaster recovery inimical environment monitoring (where fixed wired infrastructure is not available)

2. Routing in Ad hoc networks In Ad Hoc Networks, routing of packets are carried out by nodes on the network. There is no fixed router assigned to the network. Figure 1 illustrates routing in an ad hoc network environment. N1 N2 N3 N5 N4 Good Link Weak Link Figure 1: Ad Hoc Network

3. Ad Hoc Routing algorithms 3.1 Source Routing Dynamic Source Routing Ad Hoc on Demand Distance Vector (AODV) 3.2 Distributed Routing Temporally Ordered Routing Algorithm (TORA) Dynamic Destination Sequence Distance Vector 3.3 Hierarchical Routing Clusterhead – Gateway Switch Routing (CGSR) Hierarchical State Routing

3.1.1 Dynamic Source Routing (DSR) Uses source routing & route caches Multiple routes Intermediate nodes do not need to update routing information No periodic messaging Protocol consists of two phases – Route Discovery & Route Maintenance Constraints: If links are asymmetric, then the destination node has to discover a route to the initial source node Path list represents additional overhead over channel High latency to subsequent delivery of the data packet Optimizations: Route request could contain a counter Cache path fragments from recent requests Passive Acknowledgement Explicit Acknowledgement

Figure 2. Route Discovery Process in DSR

3.1.2 Ad Hoc on Demand Distance Vector (AODV) Purely on demand (no routes determined until needed) Each node contains routing table of next hop information for how to get to every other node. Nodes ping with “Hello” messages to test links Only recent active nodes notified of topology changes – propagated to neighbors. Constraints: Route discovery can be an expensive operations, since it may cause a large number of request packets to be transmitted Adds latency to the subsequent delivery of the data packet. Optimizations: Caching of path fragments from recent requests Eavesdropping on neighbouring nodes to update routing tables

Figure 3. Route Discovery Process in AODV

3.2.1 Temporally Ordered Routing Algorithm TORA is proposed for highly dynamic mobile, multihop wireless networks Has three basic functions: Route creation, Route maintenance, and Route erasure. Route is created using (i) QRY packet (contains the destination-ID (did) for which the algorithm is running) and (ii) UPD packets (contains the did and the height of the node i that is broadcasting the packet, Hi) Constraints: There is potential for oscillations to occur, which is similar to the ‘count-to-infinity’ problem in distance vector routing. However oscillations are temporary.

Figure 4. Route Creation in TORA

3.2.2 Dynamic Destination Sequence Distance Vector Based on on the idea of the classical Bellman-Ford Routing Algorithm with certain improvements. Every mobile station maintains a routing table that lists all available destinations, the number of hops to reach the destination and the sequence number assigned by the destination node Constraints: Count-to-infinity, loops and unreachable regions problems Changes at one node propagates slowly through the network Ad hoc is a dynamic network environment Optimizations: Introduces a sequence number, which help to apply advertisements in correct order, thus preventing loops Damping

3.3.1 Clusterhead-Gateway Switch Routing (CGSR) CGSR is a clustered multihop mobile wireless network with several heuristic routing schemes. A cluster head selection algorithm is utilized to elect a node as the cluster head using a distributed algorithm within the cluster Constraints: Having a cluster head scheme is that frequent cluster head changes can adversely affect routing protocol performance since nodes are busy in cluster head selection rather than packet relaying. CGSR uses DSDV as the underlying routing scheme, and hence has much of the same overhead as DSDV Optimizations: Introduces a sequence number, which help to apply advertisements in correct order, thus preventing loops Damping

Figure 5 . Clusterhead-Gateway Switch Routing (CGSR) Internet cluster super cluster

3.3.2 Hierarchical State Routing The characteristic feature of HSR is multilevel clustering and logical partitioning of mobile nodes. The network is partitioned into clusters and a cluster-head elected as in a cluster-based algorithm. Constraints: It may force traffic to go through certain nodes which may be a bottleneck and which may lead to sub-optimal paths. Maintaining a hierarchy of clusters causes additional overheads

Figure 6. Hierarchical State Routing

Conclusion Despite AODV and DSR being very similar protocols, AODV is more efficient Even though AODV and DSR are categorized under source routing for this presentation they are also distributed in nature The Mobile Ad Hoc network is a rapidly changing environment where nodes are moving in and out all the time, many of the algorithms discussed earlier have very high overheads and perform poorly unless additional enhanced features are added unto them.

References [1] Jochen Schiller, “Mobile Communications”, Second Edition, 2003 [2] A. Lasebae, “Mobile and Wireless Networks” [3] http://comet.ctr.columbia.edu/~jaekwon/E6768/Adrija-presentation.pdf [4] http://www.cse.ohio-state.edu/~jain/cis788-99/ftp/adhoc_routing/