Routing Protocol EvaluationMobility ModelsRandom Waypoint MobilityRandom Waypoint PropertiesRandom Waypoint Properties (cont)Slide 6Modified Random WaypointOther Mobility ModelsRouting Performance MetricsRouting Protocol Evaluation MetricsDelivery RatioDelivery Ratio ExamplesLatencyLatency ExamplePath Length OptimalityPath Length Optimality ExampleControl OverheadControl Overhead ExampleRouting Protocol EvaluationDavid [email protected] ModelsRandom Waypoint MobilityTwo parametersPause Time (Pt)Max Speed (Vmax)Each node starts at a random locationExecutes loopPause for Pt secondsSelect a random destination (waypoint)Move to that destination at a random speed (0,Vmax)Repeat upon arrivalRandom Waypoint PropertiesAdvantagesEasy to implementAllows heterogeneous speeds and temporarily stationary nodesDisadvantagesNon-uniform node distribution (tend towards center)Un-stable instantaneous mobility (tends towards zero and oscillates)Random Waypoint Properties (cont)Random Waypoint Properties (cont)Modified Random WaypointNarrow the random speed range(.1 Vmax, .9 Vmax) instead of ( 0, Vmax )Pre-simulation mobilityMobility properties stabilize before routing and data commencesDoesn’t fix non-uniform node distributionOther Mobility ModelsBilliard ModelNode selects a random direction, speed, and timeMoves in that direction at that speed for that time and then repeats (may have pause time as well)Bounces off simulation boundary like a “billiard ball”Maintains uniform node distribution, and uniform average speed (due to time selection)Group mobility patternsNode mobility is sum of group mobility and individual mobilityUsed by clustering based routing protocols (well suited for certain applications like the military)Trace based mobility patternsRecord real life people/vehicle/etc. motion patternsRequires location hardware such as GPSDifficult to try variations or change “parameters”Routing Performance MetricsRouting Protocol Evaluation MetricsFour most common metricsDelivery RatioLatencyPath Length OptimalityControl OverheadDelivery RatioNumber of packets successfully received by the destination / number sent by the sourceEvaluated by setting up a number of “test” flows in the networkCommonly a number of constant bit rate (CBR) flows with a specified number of packets per secondUses UDP so every dropped packet results in a reduction of the delivery ratio (no end-to-end retransmissions)Congestion SensitiveA large enough test load will result in reduced delivery ratio for ANY protocol due to congestionMobility SensitiveIf the routing protocol does not respond quickly to topology change, then packets sent on links that no longer exist will be lostDelivery Ratio ExamplesDelivery Ratio vs. Test Load Delivery Ratio vs. MobilityLatencyThe time between the creation of a packet and its delivery to the destinationUsually measured using the same setup as delivery ratioCongestion sensitiveLatency will drastically increase as the congestion limit is reached (due to waiting in large buffers)Retransmission sensitiveProtocols that locally recover packets will achieve higher delivery ratio but will increase latencyOn-demand sensitiveProtocols that setup routes after data is sent will have higher latency on the initial packets of a flowLatency ExamplePath Length OptimalityThe difference between the length of the path used for sending packets in the protocol and the length of the best possible pathMeasurementProtocol path length observed for each packet using test flowsBest possible path computed offline using same mobility patternMeasure of protocol’s ability to track good routesExtra hops from non-optimal routes will result in increased congestion and medium utilizationPath Length Optimality ExampleControl OverheadNumber/size of routing control packets sent by the protocolCalculated using counters while simulating with test flowsSometimes expressed as a ratio of control to dataIndication of how efficiently a routing protocol operatesHigh control overhead may adversely affect delivery ratio and latency under higher loadsControl Overhead
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