Page 2 Lecture Notes in Computer Science 2865 Edited by G. Goos ...
Page 2 Lecture Notes in Computer Science 2865 Edited by G. Goos ...
Page 2 Lecture Notes in Computer Science 2865 Edited by G. Goos ...
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28 P. Narayan and V.R. Syrotiuk2.2 An Overview of the DSR and AODV Rout<strong>in</strong>g ProtocolsDynamic Source Rout<strong>in</strong>g. The Dynamic Source Rout<strong>in</strong>g (DSR) protocol [11]is an on-demand rout<strong>in</strong>g protocol that allows nodes to dynamically discover asource route to any dest<strong>in</strong>ation <strong>in</strong> the network. In source rout<strong>in</strong>g, the source isresponsible for comput<strong>in</strong>g the route that a packet should take.When a node wishes to communicate with another node, it employs routediscovery to flood a control packet, called a route request (RREQ), through thenetwork, <strong>in</strong> search of a route to the dest<strong>in</strong>ation. A RREQ packet with a target oft is broadcast <strong>in</strong> the network. It is forwarded hop-<strong>by</strong>-hop from the node <strong>in</strong>itiat<strong>in</strong>gthe route discovery. When the RREQ reaches the dest<strong>in</strong>ation t or a node thatis aware of a route to t, forward<strong>in</strong>g stops. A route reply (RREP) packet is sentback to the source s on the reverse path, <strong>in</strong>clud<strong>in</strong>g a full source route to thedest<strong>in</strong>ation t. This source route is <strong>in</strong>cluded <strong>in</strong> the header of each data packetsent to t and enables stateless forward<strong>in</strong>g. Data sent to t <strong>by</strong> an application isbuffered at s until a route reply with a route to t is received, at which po<strong>in</strong>t,these packets are forwarded to t along the acquired route.The route ma<strong>in</strong>tenance mechanism monitors the status of source routes <strong>in</strong>use, detects l<strong>in</strong>k failures and repairs routes with broken l<strong>in</strong>ks. When route ma<strong>in</strong>tenance<strong>in</strong>dicates that a source route is broken, s can attempt to use any otherroute it happens to know to t, or the source s can <strong>in</strong>voke route discovery aga<strong>in</strong>to f<strong>in</strong>d a new route.Ad Hoc on Demand Distance Vector. The Ad hoc On Demand DistanceVector (AODV) [16] rout<strong>in</strong>g protocol is also an on-demand protocol. Similar totraditional distance vector protocols, AODV ma<strong>in</strong>ta<strong>in</strong>s rout<strong>in</strong>g tables with oneentry per dest<strong>in</strong>ation.AODV builds routes us<strong>in</strong>g RREQ and RREP control packets similar to theroute discovery mechanism <strong>in</strong> DSR. A node receiv<strong>in</strong>g the RREQ packet maysend a RREP if it is either the dest<strong>in</strong>ation or if it has a route to the dest<strong>in</strong>ationwith correspond<strong>in</strong>g sequence number greater than or equal to that conta<strong>in</strong>ed <strong>in</strong>the RREQ. Otherwise, it rebroadcasts the RREP. As a RREP propagates backto the source, nodes set up forward path entries to the dest<strong>in</strong>ation <strong>in</strong> their routetables. Once the source node receives the RREP it may beg<strong>in</strong> to forward datapackets to the dest<strong>in</strong>ation.There are several differences <strong>in</strong> the route discovery mechanisms of DSR andAODV. The source rout<strong>in</strong>g mechanism used <strong>in</strong> DSR enables s to learn routestowards each <strong>in</strong>termediate node on the route to t. Additionally, each <strong>in</strong>termediatenode on the path from s to t may learn routes to every other node on the route.In DSR, the dest<strong>in</strong>ation node replies to all RREQs sent towards it dur<strong>in</strong>g as<strong>in</strong>gle request cycle. Thus, <strong>in</strong> DSR, the source learns many alternate routes tothe dest<strong>in</strong>ation <strong>in</strong> contrast to AODV where the dest<strong>in</strong>ation replies only to thefirst arriv<strong>in</strong>g request.