PeformanceEvaluationOfAdHocOnDemandRouting.doc

/kmust1peformance evaluation of ad hoc on demand routingprotocol with heterogenous nodesmahamadou laico traoreschool of continued education，beijing university of posts and telecommunications，beijing（100876）abstractin wireless ad hoc network many papers have been proposed on the routing protocols implementation,analysis, performance study and improvement. simulations are always done with identical nodes assumption thats means nodes homogeneity, all of the nodes have the same characteristics but in reality it is not always true. with the multiplicity of the wireless devices sometimes it is possible; nodes can be different in some parameters like coverage range, antenna height, energy and rate of response to incoming signal. since many kinds of nodes with different parameters are available and for the extensibility of wireless ad hoc network, it is time to begin to think on how to introduce and to take this constraint into account in the current routing protocols. so for showing heterogeneity constraint in these routing protocols, we will propose to study the behaviors, and the performance limitation of ad hoc on demand distance vector protocol (aodv) which is one of the ietf approved protocols.keywords：aodv，heterogeneity，coverage range and antenna height1. introductiona mobile ad-hoc network is a kind of wireless network which has mobile devices with self-configuring capability, the terminals may be free to move randomly and organize themselves arbitrary, and thus, the network topology may change rapidly and unpredictably; consequently causing several particular features to limit the achievable performance of data communications, such as radio link problems, energy constrained operation and the lack of infrastructure. with these constraints the key element which can offset, influence and improve the network efficiency is the routing protocol.ideally, a mobile ad hoc network routing protocol should be able to quickly provide optimal routes, even in the case of link failures in an active path, with minimum impact on data latency, available bandwidth and device power consumption for any data traffic pattern. apart from theses constraints so far mentioned we still face the problem of node heterogeneity which is now a real challenge in current manet routing protocols with the proliferation, the development and the multiplicity of wireless devices. till now in many proposed paper routing protocols implementation, performance analysis and improvement are done with homogeneous nodes assumptions, thats means all of the nodes are having the same characteristics when making routing decisions; which treats a resource-poor (weak) device forwarding data packets same as a resource-rich (strong) device, which is totally different from the real conditions. so in order to extend the application area of the wireless ad hoc network, i think it is time and necessary to adapt or include these new constraints in current approved protocols or to plan a new protocol with heterogeneous nodes assumptions.heterogeneity is just a case that wireless ad hoc networks consist of many different devices. these devices may include of some dedicated wireless routers, desktop machines, laptops, handhelds and phones. each device in the network has its own characteristics, properties and purpose such as energy capacity, response speed and coverage range and should be used accordingly.some papers have already talked on a similar problem but many of them are based on the hierarchical routing protocol assumptions 6 and 7, which generally have an incumbent problem of group or group head selection when nodes movement is very fast. due to the importance and to bring to fore this problem we propose to analyze the behavior, the limit performances of the ad hoc on demand distance vector protocol (aodv) , which is one of the ietf approved protocol, when nodes are heterogeneous and mixed distributed./kmust1this paper is organized as follows: section ii is the ad hoc network protocols overview; section iii, simulation and result analysis and the last section is the paper conclusion and future work proposal.2. ad hoc network protocols overviewmobile ad-hoc networks are networks that involve mobile nodes communicating over wireless connections. the networks are characterized by variable topologies, therefore static routing paths, like those used in conventional routing, cannot be used. the dynamic properties of links within a manet require active topology discovery and maintenance to do any kind of deterministic routing. continual variability, along with the existence of sudden and possibly unidirectional connections, makes routing on these networks very complex. approaches, termed pro-active 8, work much like traditional link-state routing algorithms, these approaches attempt to maintain an up to date view of the network locally and use this information to route packets towards their destination: example of pro-active routing protocol is dsdv (destination sequenced distance vector). but these approaches have been found not to scale well, requiring exponentially increasing control traffic in order to maintain their connection state information. therefore, another approach was developed that could scale without the need of consistent control traffic: reactive routing. 9, the idea behind reactive routing is to only find connection state when it is needed. when a message is to be sent, a node floods the network with a route request. everyone that hears the request appends their address and forwards the request. once the destination is found, the request is routed back to the source using the appended addresses. the source then uses the list of addresses to route the message to its final destination. this incurs an extra round trip latency and higher chance of route failure in exchange for control traffic that scales linearly with the amount of messages to be sent. in the other hand we have another approach which merges proactive and reactive protocol. called hybrid routing protocol 10 and 11, it combines the best features of the above two categories. nodes within a certain distance from the node are said to be within the routing zone of the given node. for routing within this zone, a table-driven routing approach is used; for nodes that are located beyond this zone, an on-demand routing approach is used. example of hybrid routing protocols is zrp (zone routing protocol).ad hoc on-demand vector routing (aodv) 1, 2, 3 and 4 protocol is a reactive routing protocol for mobile ad hoc networks. that means that aodv does nothing until a node needs to transmit a packet to a node for which it does not know a route. in addition, it only maintains routes between nodes which need to communicate. its routing messages do not contain information about the whole route path, but only about the source and the destination. therefore, routing messages have a constant size, independently of the number of hops of the route. it uses destination sequence numbers to specify how fresh a route is (in relation to another), which is used to grant loop freedom. in aodv, a node does route discovery by flooding the network with a route request message (rreq). once it reaches a node that knows the requested route, it replies with a route reply message (rrep) that travels back to the originator of the rreq. after this, all the nodes of the discovered path have routes to both ends of the path. in addition to these routing messages, route error messages (rerr) are used to notify the other nodes that certain nodes are not anymore reachable due to a link breakage.3. simulation and result analysisthe simulation experiments are presented in this section. the overall goal of our experiments is to study and show the behavior, the performance of the ad-hoc on demand routing protocol to react to the network heterogeneity by computing the number of weak devices. it will be evaluated on the end-to-end throughputs, average delay and network average overhead for the case of two different classes, strong and weak devices which are mixed distributed in the network area.3.1 simulation environmentour simulations have been implemented in network simulator (ns-2) 5 from lawrence berkeleynational laboratory with extensions from the monarch project at carnegie mellon university. at the physical layer, the extended ns-2 employs a radio propagation model supporting propagation delay, omni-directional antennas, and a shared media network interface. the ieee 802.11 medium access protocol is employed at the link layer level.our simulations are based on the scenario of 30 wireless nodes forming an ad hoc network, moving about over a rectangular (1200mx1200m) flat space. all the nodes are mixed distributed and they are composed of weak and strong terminals. the nodes in the simulation are mixed distributed and move according to the random waypoint model without pause time or total movement. each node selects a random destination in the 1200m x 1200m space and moves to that destination at a speed distributed uniformly between 0 and 20m/s and each simulation runs for 400s of simulated time.we run our simulations by varying the number of weak nodes patterns generated for 5 different simulations: 5, 10, 15and 20. the case of 30 homogenous nodes has been chosen as strong nodes.three cases of heterogeneity are created and described as follow:-case 1: coverage range difference, the strong nodes have 250m as coverage range and the weak nodes, 100m as coverage range.- case 2: antenna height difference, we define two kinds of antenna heights, 1.5m for the strongdevices and 0.5 m for the weak devices.- case 3: case 1 and case 2 combined together3.2 simulation resultswe studied the protocol performance by computing the network throughput, network overhead and the end to end communication average delay. in the simulation environment assumptions, the behaviors and the performances of ad hoc on demand distance vector protocol (aodv) for the three cases of heterogeneity are illustrated by below graphs. these graphs correspond successively to the networkaver a g e dela yaverage delay, overhead and throughput graphs.1210864antenna height coverage range coverage&ant-height200510152025number of weak nodesfig 1: average delaysince the nodes are distributed, mixed randomly; it is possible for an end-to-end link, that the number of weak nodes is higher than the strong nodes; what results in a bad packet routing due to theirs weak characteristics; thus causing the increase in averageend-to-end communication delay.indeed, on the graph fig 1 we observe that this delay is more notable in the third case of heterogeneity than in both other cases. the graph also shows that the delay for a difference of antenna height is smaller than the delay caused by the difference in coverage range. since the coverage range of nodes is not the same; then link become asymmetrical i.e. sometimes it possible that a node a communicates with a node b but b in turn cannot communicate with a node c because of the weakness of its coverage range. thus there is a link break which demands that the process of local repair or new route discoverymechanisms be executed which ultimately increase the average delay time.for all the three cases of heterogeneity, average delay time increases with the number of weak nodes. it reaches 9s for the third case of heterogeneity which is the mix of the two others cases. this value is approximately eight times of the result of the heterogeneous nodes delay time under the sameconditions of simulation.20000ov er hea d15000100005000antenna height coverage coverage&ant-height00510152025number of weak nodesfig 2: overheadin addition to the frequent link breaks which results in the frequent request of the local repair or route discovery mechanisms, we also have the problem of packets loss.packet loss occurs in the case where data packets transmission is cancelled due to routing time out caused by weak characteristics of the communication link. faced with these different constraints the network uses more control packets and have as consequence a spectacular increase in network routing overhead.the graph in fig 2 above shows all the three cases of heterogeneity, the network routing overheadtends towards 2 times the value of the homogenous case for 20 weak nodes.8070throughput60504030201000510152025 number of weak nodesantenna height coverage range coverage&ant- heightfig 3: throughputbecause of the rise in the end-to-end communication average delay time and the network routing overhead which normally occupy most of the available bandwidth and as one would expect it will have a serious consequences on the network throughput. indeed we can notice this on the graph where the throughput decreases with the growth in number of the weak nodes. we can see, it decreases by 81% for coverage range difference and by 97% for antenna height difference from the homogenous value for only 10 numbers of weak nodes and certainly the result will reach zero when the number of weaknodes reaches 25.4. conclusionstoday research in ad hoc network is the most covet topic by the researchers due to its application area. till now, the proposed protocols of this kind of network have been implemented with the nodes assumed to be homogenous in nature that means all the nodes in the network are assumed to have the same characteristics. according to the above simulations results obtain in this paper, due to some differences in characteristics between the wireless devices, such as there coverage range, node antenna height; it is obvious that the end-to-end communication average delay time, the network routing overhead and throughput are very much affected. we can say that the protocol dont respond as well as in the case of homogenous node assumptions and thus, we think it is time to take into account or accommodate heterogeneity constraint in current ad hoc network protocols to improve more their performances. and we think it is inescapable now because of the actual development and multiplicity of the wireless devices, especially as the cases of heterogeneity mentioned in this paper are only few among many others yet to be mentioned.future workour future work in ad hoc network routing protocols improvement will be how to accommodate ad hoc on demand routing protocol to support nodes heterogeneity or implement a new one which takes into account this constraint.references1- c. e. perkins, e. m. belding-royer, and s. das “ad hoc on-demand distance vector (aodv) routing”rfc 3561, july 2003.2- mobile ad-hoc networks, /html.charters/manetcharter.html.3- c. perkins and e. royer and s. das “ad hoc on-demand distance vector (aodv) routing”, internet draft, draft-ietf-manet-aodv-11.txt, work in progress, aug 2002.4- c. perkins and e. royer, “ad-hoc on-demand distance vector routing” in ieee workshop on mobilecomputing systems and applications, february 1999.5- the ns manual (formerly ns notes and documentation)the vint project a collaboration between researchers at uc berkeley, lbl, usc/isi, and xerox parc.kevinfall i, editor kannan varadhan i, editor september 23, 20066- efficient group mobility