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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Proactive QoS Rout<strong>in</strong>g <strong>in</strong> Ad Hoc Networks 61performance? Or should we just give up on proactive QoS rout<strong>in</strong>g? The goal of thispaper is to <strong>in</strong>vestigate the answers to these questions through the performance evaluationof a proactive bandwidth QoS rout<strong>in</strong>g algorithm that we have proposed.In [5], we studied the approach of proactive QoS rout<strong>in</strong>g and proposed 3 heuristicsthat allow OLSR (Optimized L<strong>in</strong>k State Protocol [8]) to pre-compute the best bandwidthroute among all the possible routes. That work presents the performance of theheuristics <strong>in</strong> a static network. In this paper, we implement one QoS OLSR heuristic,which guarantees to f<strong>in</strong>d the best bandwidth path <strong>in</strong> the static network and has comparablylow overhead, <strong>in</strong> OPNET and evaluate the rout<strong>in</strong>g algorithm’s performance withnode movements and data flows, and consequently, analyze the feasibility of proactiverout<strong>in</strong>g <strong>in</strong> MANET.The rest of the paper is organized as follows: a brief description of OLSR and QoSversions of OLSR is given <strong>in</strong> Section 2. The detailed implementation of QoS OLSR <strong>in</strong>OPNET is discussed <strong>in</strong> Section 3. Section 4 lists the OPNET simulation parametersand discusses the simulation results <strong>in</strong> OPNET. Section 5 analyses whether proactiveQoS rout<strong>in</strong>g is practical <strong>in</strong> an Ad-Hoc network and discusses future work.2 OLSR and QoS OLSRThe IETF’s MANET Work<strong>in</strong>g Group has <strong>in</strong>troduced the Optimized L<strong>in</strong>k State Rout<strong>in</strong>g(OLSR) protocol for mobile Ad-Hoc networks [8]. The protocol is an optimizationof the pure l<strong>in</strong>k state algorithm. The key concept used <strong>in</strong> the protocol is that ofmultipo<strong>in</strong>t relays (MPRs). The MPR set is selected such that it covers all nodes thatare two hops away. A node’s knowledge about its neighbors and two-hop neighborsis obta<strong>in</strong>ed from HELLO messages – the message each node periodically generates todeclare the nodes that it hears. The node N, which is selected as a multipo<strong>in</strong>t relay <strong>by</strong>its neighbors, periodically generates TC (Topology Control) messages, announc<strong>in</strong>gthe <strong>in</strong>formation about who has selected it as an MPR. Apart from generat<strong>in</strong>g TCsperiodically, an MPR node can also orig<strong>in</strong>ate a TC message as soon as it detects atopology change <strong>in</strong> the network. A TC message is received and processed <strong>by</strong> all theneighbors of N, but only the neighbors who are <strong>in</strong> N’s MPR set retransmit it. Us<strong>in</strong>gthis mechanism, all nodes are <strong>in</strong>formed of a subset of all l<strong>in</strong>ks – l<strong>in</strong>ks between theMPR and MPR selectors <strong>in</strong> the network. So, contrary to the classic l<strong>in</strong>k state algorithm,<strong>in</strong>stead of all l<strong>in</strong>ks, only small subsets of l<strong>in</strong>ks are declared. For route calculation,each node calculates its rout<strong>in</strong>g table us<strong>in</strong>g a “shortest hop path algorithm” basedon the partial network topology it learned. MPR selection is the key po<strong>in</strong>t <strong>in</strong> OLSR.The smaller the MPR set is, the less overhead the protocol <strong>in</strong>troduces. The proposedheuristic <strong>in</strong> [8] for MPR selection is to iteratively select a 1-hop neighbor that reachesthe maximum number of uncovered 2-hop neighbors as an MPR. If there is a tie, theone with higher degree (more neighbors) is chosen.Table 1. Node B’s MPR(s), based on Fig. 1.Node 1 Hop Neighbors 2 Hop Neighbors MPR(s)B A, C, F, G D, E CFrom the perspective of node B, both C and F cover all of node B’s 2-hopneighbors. However, C is selected as B’s MPR as it has 5 neighbors while F only has4 (C’s degree is higher than F).