Impact of Link Discovery Delay on Optimized Link State Routing Protocol for Mobile ad hoc Networks

Transcription

1 Impact of Link Discovery Delay on Optimized Link State Routing Protocol for Mobile ad hoc Networks Akhila Kondai Problem Report submitted to the Benjamin M. Statler College of Engineering and Mineral Resources at West Virginia University in partial fulfillment of the requirements for the degree of Masters of Science in Computer Science Approved by Dr. Vinod Kulathumani, Ph.D, Chair Dr. Brian Woerner, Ph.D Dr. Roy Nutter, Ph.D Lane Department of Computer Science and Electrical Engineering Morgantown, West Virginia 2014 Keywords: Routing Protocols, OLSR, Routing, MANET, Link Discovery Delay Copyright 2014 Akhila Kondai

2 ABSTRACT Impact of Link Discovery Delay on Optimized Link State Routing Protocol for Mobile ad-hoc Networks Akhila Kondai A Mobile ad hoc Network (MANET) is an infrastructure-less, continuously self-configuring network of mobile devices. Due to this dynamic link changes, point to point communication has always been a challenge in mobile ad hoc networks. To achieve routing, each node has to constantly keep updating other nodes in the network about its local neighborhood changes, without relying on a predefined infrastructure for doing so. It has always been believed that limited bandwidth or capacity of the networks to carry out this route advertisement is the reason behind poor route availability in mobile ad-hoc networks. In this report, we examine if network capacity is actually a significant factor behind poor route availability in MANET s or are there any other parameters that have more significant impact on the route availability than network capacity. Specifically we explore an alternate parameter, namely the neighborhood discovery time, and examine its impact on route availability. For this, we consider Optimized Link State Routing protocol (OLSR), a popular routing protocol for MANET and analyze route quality and capacity utilization under different discovery intervals. In OLSR protocol, HELLO messages and Topology Control (TC) messages are exchanged between nodes, to discover neighbors and then disseminate link state information throughout the mobile ad hoc network. We use NS3 to simulate large dense mobile networks and to compare the difference in number of number of available valid routes in the network when changing the HELLO and TC intervals. We study this under different scenarios like varying network size, varying node density, and varying link changes in the mobile network.

3 ACKNOWLEDGEMENTS I would like to thank Dr. Vinod Kulathumani for all the support and guidance he has given me throughout my project. I would also like to acknowledge Dr. Brian Woerner and Dr. Roy Nutter for being part of my committee. I would also like to thank all my friends and family members for their continuous support. Finally, I would like to thank the most important people in my life, my parents and my siblings for their unconditional love, support, encouragement, and trust towards me. i

4 TABLE OF CONTENTS 1. Introduction Background Problem Statement Optimized Link State Routing Protocol OLSR Overview Multipoint Relays Neighbor Discovery and Link sensing MPR Selection Topology Discovery Routing Table Calculation Soft State Signaling in OLSR Implementation Measuring Route Availability Broken Routes Looped Routes No Paths Available Routes Based on True Positions Metrics Measured Results and Observations Impact of varying HELLO Interval Impact of varying TC Interval Impact of Refresh Intervals on Networks with Different Node Densities and Fixed Network size Impact of HELLO Interval on Networks with Different Sizes and Fixed Node Densities For Node Density of ii

5 4.4.2 For Node Density of For Node Density of For Node Density of For Node Density of Impact of Refresh Intervals on Network Utilization Conclusion Future Work Bibliography iii

6 LIST OF FIGURES Figure 1.1: Valid Path Ratio Vs Time (N=100; D=8, LC=0.5, HI=2, TC=5)... 3 Figure 1.2: Network Utilization across all the nodes (N=100; D=8, LC=0.5, HI=2, TC=5)... 4 Figure 2.1: Multipoint Relays [1]... 7 Figure 3.1: Route between source node X and destination node Y Figure 3.2: Broken Route between source node X and destination node Y Figure 3.3: Looped Route between source node X and destination node Y Figure 3.4: Initial position of nodes at the start of simulation Figure 3.5: Snap shot of the simulation at time = 0.6 seconds Figure 3.6: Snap shot of the simulation at time = 6.75 seconds Figure 4.1: Paths Ratio vs Time (N=100; D=8, LC=0.3, HI=2, TC=5) Figure 4.2: Paths Ratio vs Time (N=100; D=8, LC=0.3, HI=1, TC=5) Figure 4.3: Paths Ratio vs Time (N=100; D=8, LC=0.3, HI=0.5, TC=5) Figure 4.4: Paths Ratio vs Time (N=100; D=8, LC=0.3, HI=0.25, TC=5) Figure 4.5: Paths Ratio vs Time (N=100; D=8, LC=0.3, HI=0.1, TC=5) Figure 4.6: Broken Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI Varying, TC = 5s) Figure 4.7: Looped Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI Varying, TC = 5s) Figure 4.8: No Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI Varying, TC = 5s) Figure 4.9: Valid Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI Varying, TC = 5s) Figure 4.10: Paths Ratio vs Time (N=100; D=8, LC=0.5, HI=2, TC=5) Figure 4.11: Paths Ratio vs Time (N=100; D=8, LC=0.5, HI=1, TC=5) Figure 4.12: Paths Ratio vs Time (N=100; D=8, LC=0.5, HI=0.5, TC=5) Figure 4.13: Paths Ratio vs Time (N=100; D=8, LC=0.5, HI=O.25, TC=5) Figure 4.14: Paths Ratio vs Time (N=100; D=8, LC=0.5, HI=0.1, TC=5) Figure 4.15: Broken Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.5, HI Varying, TC = 5s) Figure 4.16: Looped Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.5, HI Varying, TC = 5s) Figure 4.17: No Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.5, HI Varying, TC = 5s) Figure 4.18: Valid Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.5, HI Varying, TC = 5s) Figure 4.19: Broken Paths Ratio vs Refresh intervals (N=100; D=8, LC Varying, HI Varying, TC = 5s) Figure 4.20: Looped Paths Ratio vs Refresh intervals (N=100; D=8, LC Varying, HI Varying, TC = 5s) Figure 4.21: No Paths Ratio vs Refresh intervals (N=100; D=8, LC Varying, HI Varying, TC = 5s) Figure 4.22: Valid Paths Ratio vs Refresh intervals (N=100; D=8, LC Varying, HI Varying, TC = 5s) Figure 4.23: Broken Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI=2s and 0.1s, TC Varying) iv

7 Figure 4.24: Looped Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI=2s and 0.1s, TC Varying) Figure 4.25: No Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI=2s and 0.1s, TC Varying) Figure 4.26: Valid Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI=2s and 0.1s, TC Varying) Figure 4.27: Valid Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.5, HI=2s and 0.1s, TC Varying) Figure 4.28: Broken Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.29: Broken Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=0.1s, TC=5s) 39 Figure 4.30: Broken Paths Ratio vs Node Densities (N=100, Varying Densities, LC=0.3 & 0.5,HI=0.1,TC=0.25) 40 Figure 4.31: Looped Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=2s, TC=5s).. 40 Figure 4.32: Looped Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=0.1s, TC=5s) 41 Figure 4.33: Looped Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5,HI=0.1,TC=0.25) 41 Figure 4.34: No Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.35: No Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.36: No Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=0.1, TC=0.25s) Figure 4.37: Valid Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.38: Valid Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.39: Valid Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=0.1, TC=0.25s) 44 Figure 4.40: Broken Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.41: Broken Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.42: Looped Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.43: Looped Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.44: No Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.45: No Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.46: Valid Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.47: Valid Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.48: Broken Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.49: Broken Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.50: Looped Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.51: Looped Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.52: No Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.53: No Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.54: Valid Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.55: Valid Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.56: Broken Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.57: Broken Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=0.1s, TC=5s) v

8 Figure 4.58: Looped Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.59: Looped Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.60: No Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.61: No Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.62: Valid Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.63: Valid Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.64: Broken Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.65: Broken Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.66: Looped Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.67: Looped Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.68: No Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.69: No Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.70: Valid Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.71: Valid Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.72: Broken Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.73: Broken Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.74: Looped Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.75: Looped Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.76: No Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.77: No Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.78: Valid Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.79: Valid Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.80: Valid Paths Ratio vs Varying Refresh Intervals Figure 4.81: Network Utilization by the nodes in a network for different refresh intervals vi

9 1. Introduction 1.1 Background A Mobile ad hoc Network (MANET) is an infrastructure-less, continuously self-configuring network of mobile devices. With the significant increase in popularity of mobile devices and wireless networks, mobile ad hoc networks has become one of the most active and vibrant field of networks and communications. Application areas of MANET s include [30]: Tactical Networks: Used in Military battlefield for communications between soldiers, military vehicles and military information headquarters. Emergency Services: MANET s can be used in emergency situations for search and rescue operations during disaster recovery. In case of environmental disasters where infrastructure-less networks would be needed, MANET s play a very vital role Vehicular Services: Used for communicating between vehicles and devices within the vehicles for providing road or accident guidance and transmission of road and weather conditions. Sensor Networks: Used in home applications for communicating with smart sensors and actuators embedded in consumer electronics. Commercial and civilian Environments: Used in E-Commerce for electronic payments anytime and anywhere, Used in universities and campus settings for creating virtual classrooms, Used in entertainment for multi-user games, Wireless P2P networking, Used in home and enterprise networking for Personal Area Network (PAN). With the advent of ad hoc network based applications, MANET has been one of the most active areas of research for the past fifteen years. Due to dynamic link changes, point to point communication has always been a challenge in mobile ad hoc networks. Routing in MANETs has been an active area of research for the past two decades. Currently, several types of routing protocols exist to solve the problem of routing in mobile ad hoc networks in one way or the other. These protocols can be classified into three main categories: Ondemand, Table-driven, Hybrid protocols based on the approach they use to seek routes to the destination node [5]. On-demand routing protocols adopt the reactive routing approach where the protocol does not take an initiative for finding routes to a destination unless it is required. The disadvantages with this type of routing protocols is that there would be excessive flooding when a request for route is made and latency time in finding a route is also high [29]. Routing protocols like ad hoc On-demand Distance 1

10 Vector (AODV) [24], Dynamic Source Routing (DSR) [25] and Temporary Ordered Routing Protocol (TORA) [26] come under this section of routing protocols. Table-driven routing protocols adopt the proactive routing approach where the protocol always maintains routes to destination nodes by periodically exchanging control messages throughout the network. The disadvantage with this class of routing protocols is that the routes which are determined in advance have to be updated constantly whenever the topology changes and how fast the protocol reacts to these changes decides its routing efficiency [29]. Routing protocols like Optimized Link State Routing Protocol (OLSR) [1, 3], Destination Sequence Distance Vector (DSDV) [27] are examples of Table-driven proactive routing protocols. The third category of routing protocols is Hybrid protocols which combines the advantages of both reactive and proactive routing protocols. Example of Hybrid protocols is Zone Routing Protocol (ZRP) [28] which uses both proactive and reactive components [1, 5]. In this report we analyze the Optimized Link State Routing protocol (OLSR) in large and dense mobile networks. 1.2 Problem Statement The primary challenge in building a mobile ad hoc network is to have a robust routing protocol for equipping each device to continuously keep updating other nodes in the network about its local neighborhood changes to properly route traffic. It has always been believed that limited bandwidth or capacity of the networks to carry out this route advertisement is the reason behind poor route availability in mobile ad-hoc networks. In this report, we explore an alternate parameter, namely the neighborhood discovery time, and examine its impact on route availability. In this report, we consider OLSR, a popular routing protocol for MANET and analyze route quality and capacity utilization under different discovery intervals. OLSR is an optimization of internet s classical Link State Routing Algorithm, which has been tailored to suit the requirements of mobile ad hoc networks. The message overhead as compared to a classical flooding mechanism is reduced in this protocol by forming a two level hierarchy using the concept of Multipoint Relays (MPRs). Instead of every node that receives the broadcast packet retransmitting them, only a set of nodes in the neighborhood are selected to do the retransmission. This set of neighbor nodes which retransmit the packets it receive are called as Multipoint Relays (MPR) of that node [1]. 2

11 Time Valid Path Ratio If we consider the flooding issue which exists in the classical link state routing protocol, the number of retransmissions of broadcast packets are decreased considerably using the concept of Multipoint Relays. But the problem of poor availability of routes still remains the same. This can be seen in the Figure 1.1 where the number of available valid paths in the routing tables generated using the default parameters of OLSR are plotted across time for a network of size 100 nodes, node density of 8 and rate of link changes per node is Time ValidPathRatio Figure 1.1: Valid Path Ratio Vs Time (N=100; D=8, LC=0.5, HI=2, TC=5) We analyzed the traffic flow in the above network where nodes run the OLSR protocol using the default parameters to know the utilization of the network. Each nodes maximum data rate in the network is 11 Mbps. Because of interference and collisions, we assume each node gets at least 10% of its total capacity, that implies each node has a data rate of 1.1 Mbps for transferring data. Figure 1.2 shows the average network utilization throughout all the nodes in the network. 3

12 Figure 1.2: Network Utilization across all the nodes (N=100; D=8, LC=0.5, HI=2, TC=5) From Figure 1.1 and Figure 1.2, it is clearly evident that the average number of valid routes is just around 20% - 50% of the actual available routes, even though the network is very poorly utilized (0.023 Mbps out of 1.1 Mbps, which is around 2% of the network capacity). Therefore we can say that network capacity is actually not the significant factor behind poor route availability in MANET s. In this report, we try to understand what else could affect the route availability in MANET s. Specifically we explore an alternate parameter, namely the neighborhood discovery time, and examine its impact on route availability. In large dense mobile networks, nodes are free to move frequently and randomly, organizing themselves arbitrarily. Nodes can join or leave the network anytime, causing the link connectivity to change unpredictably and rapidly. Whenever the link connectivity between nodes in a network change, the routing protocols take time to detect the link failure and to re-establish a consistent view of the new topology. During this transient period, before the routing tables gets updated with the recent link changes that occurred, there would be routes in the routing table with failed links/nodes somewhere along the path due to the recent node movement and link changes. All the data packets which are forwarded along such routes with failed links/nodes will be dropped. Sometimes failed links/nodes could also lead to inconsistencies in the routing tables causing routing loops. Therefore for a routing protocol to work 4

13 efficiently, it is important that the protocol discovers these link changes, get a stable view of the new topology and update the routing tables with the recent link changes with very less delay [4]. OLSR protocol uses HELLO messages and Topology Control (TC) messages, to discover neighbors and then disseminate link state information throughout the mobile ad hoc network [9]. These messages are periodically exchanged in the network. HELLO interval and TC interval are the refresh interval timers used in OLSR to decide the rate at which HELLO messages and TC messages are exchanged between the nodes within the mobile ad hoc network. In this report, we perform a detailed analysis on how tuning of refresh intervals, network size variation, and node density variation impacts the accuracy of routing tables. We study the effects of tuning refresh intervals like HELLO interval and TC interval on the number of available valid routes in the routing tables stored at every node in the network at any given point of time. A route in a routing table from a source node to destination node is said to be valid, if there is no link failure or loop formations along the entire path between the source and destination. We assume that when a packet is forwarded through an available valid route, it does not get dropped and reaches the destination successfully, thereby increasing the performance and efficiency of the OLSR protocol. We use NS3 to simulate large dense mobile networks to compare the difference in number of number of available valid routes in the network when changing the HELLO and TC intervals. We study this under different scenarios like varying network size, varying node density, and varying link changes in the mobile network. 5

14 2. Optimized Link State Routing Protocol 2.1 OLSR Overview Optimized Link State Routing Protocol is a proactive table driven routing protocol used in mobile ad hoc networks. OLSR is an optimization of internet s classical Link State Routing Algorithm, which has been tailored to suit the requirements of mobile ad hoc networks. Optimization in OLSR is achieved in two ways. Firstly, the size of control packets used is reduced by declaring only a subset of links with its neighbors who are its Multipoint Relay Selectors, instead of all the links with its neighbors. Secondly, it reduces the number of transmissions in a flooding or broadcast procedure by only letting the Multipoint Relays of the node to retransmit its broadcast messages. This way, each node minimizes the flooding of control traffic by only using selected nodes to diffuse its messages in the network. The more dense and large the network is, better the optimization achieved [1, 3]. OLSR is designed in a completely distributed manner and does not depend on any central entity. Control messages are periodically exchanges between nodes to maintain topology information of the entire network in presence of mobility. OLSR mainly uses two type of control messages: HELLO messages and Topology Control (TC) messages to discover neighbors and then disseminate link state information throughout the mobile ad hoc network. HELLO messages perform the task of link sensing, neighbor detection and MPR signaling and TC messages perform the tasks of advertising the link states in the network [3]. OLSR uses soft-state signaling approach, so apart from the normal periodic control messages, the protocol does not generate any extra control traffic in response to link additions and link failures [3, 4]. 2.2 Multipoint Relays The concept of Multipoint Relays is used in OLSR protocol to minimize the flooding of broadcast packets in the network. Instead of every node that receives the broadcast packet retransmitting it, only a set of nodes in the neighborhood are selected to do the retransmission. This set of neighbor nodes which retransmit the packets broadcasted by that are called as Multipoint Relays (MPR) of that node. All the other nodes which are not Multipoint Relays, just read and process the packet received but do not retransmit it to other nodes [3]. Every node maintains a MPR Selector Set which contains the list of neighbors which selected it as an MPR. All the broadcast messages coming from these MPR selectors of a node should be retransmitted by that node. The MPR Selector Set keeps changing over time as neighbors constantly keep changing in 6

15 a mobile ad hoc network. Whenever a node changes its MPR, it notifies the MPR in the subsequent HELLO messages [1]. For a node N, the Multipoint Relay Set, denoted as MPR (N), consists of subset of neighborhood of N such that every node in the two hop neighborhood must have a symmetric link towards MPR (N). The control traffic overhead in the network is dependent on the size of the MPR Set. If the MPR Set is small, it means there is less control traffic overhead as there are only few nodes which retransmit the packets it receives [1]. Finding the optimal MPR set is proved to be an NP-hard problem [21]. Algorithms have been developed and analyzed on selecting MPR's efficiently. Figure 2.1: Multipoint Relays [1] In Figure 2.1, bold lines represent symmetric links. Neighborhood of Node 1 is {2, 3, 4, 5, 6, 7, 8, 9} Two hop Neighborhood of Node 1 is {10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25} MPR(1) = {3,5,7,9} 7

16 2.3 Neighbor Discovery and Link sensing OLSR protocols uses HELLO messages for neighbor detection and link sensing. Every node broadcasts HELLO messages periodically to detect its neighbors up to two hops and the state of communication with its neighboring node. Whenever a node broadcasts a HELLO message, all its one hop neighbors receive it. They read and process the information in the HELLO message but do not retransmit it to other nodes. HELLO message contains information about its neighbors and their link status [1]. Every node maintains a Link Set which contains information about the node's link status with its neighboring nodes. Link status could be symmetric or asymmetric or MPR. If both the nodes can transmit data to each other, and the link between them is verified to be bi-directional then the link status would be symmetric. If HELLO messages from one node is heard and if it is not confirmed that this node is able to receive HELLO messages from the other node, then the link between them is said to be unidirectional (link status would be asymmetric) [3]. If the link status is MPR, it implies that node is selected as Multipoint Relay by this local node and link between them is bi-directional [1]. Every tuple in the Link Set is associated with a validity time, until which that link is considered to be valid and usable. Whenever a node receives a HELLO message, the Link Set would be updated. If there is no tuple in the Link Set for a neighboring node, a new tuple would be created. If there already exists a tuple, the validity time would be increased [3]. Every node also maintains a Neighbor Set which keeps information about its neighbors. There is a clear association between the Link Set and the Neighbor Set, as a node can be neighbor of another node only if there is at least one link between the two nodes. Neighbor Set would contain neighbor tuples which store information about its neighbor's status, its willingness to act as a Multipoint Relay and validity time until which that tuple would be valid. A Neighbor Set would be populated by maintaining correspondence between the link tuples and associated neighbor tuples as below [3]: When a new link appears, each time a link tuple is created, an associated neighbor tuple must also be created. When a link changes, each time a link tuple is modified, the associated neighbor tuple neighbor's status of must also be updated When a link is deleted, each time a link tuple is deleted, the associated neighbor tuple must also be removed if it has no other associated link tuples. 8

17 A 2-hop Neighbor Set is also maintained at every node, which stores the list of nodes that have a symmetric link to its symmetric one hop neighbors. Whenever a node receives HELLO messages from a symmetric neighbor, it should update its 2-hop neighbor set [3]. 2.4 MPR Selection With the information about all its one and two hop neighbors, each node can select its set of Multipoint Relays from its one hop neighbor set. A node selects its Multipoint Relays such that through the neighbors in the MPR set, it can reach all its symmetric 2 hop neighbors. The selected Multipoint Relays will know about this selection in the subsequent HELLO messages transmitted by the node that has selected it as a Multipoint Relay, as their link status would be marked as MPR. Upon receiving HELLO messages, each node constructs its MPR Selector Set which contains list of nodes who have selected it as a Multipoint Relay. A sequence number is associated with the MPR Selector Set to keep track of the most recent MPR Selector Set of a node. Whenever the MPR Selector Set changes, this sequence number is incremented to a higher value [1]. Each node also maintains a sequence number which keeps track of the most recent MPR Set selected by that node. Whenever the MPR Set changes, the sequence number is incremented to a higher value. MPR Set is recalculated whenever there is a change in the symmetric neighborhood or in the symmetric strict 2-hop neighborhood [3]. 2.5 Topology Discovery Topology Control (TC) messages are exchanged in OLSR, to provide each node in the network with sufficient link-state information to allow route calculation. Every node must at least disseminate links between itself and the nodes in its MPR Selector Set throughout the network, in order to provide sufficient information to enable routing. Every node periodically broadcasts TC messages to declare its MPR Selector Set, along with the sequence number associated with that MPR Selector Set. This sequence number will be used to verify whether the information received is more recent than what it already has. Unlike HELLO messages, TC messages are forwarded by the MPR's like the usual broadcast messages. Only the nodes which have been selected as Multipoint Relays by some other nodes, will broadcast TC messages. Other nodes which are not MPR's do not generate any TC messages as they do not have a MPR Selector Set to be advertised [1, 3]. Every node in the network maintains a Topology Information Base, which records information about the network topology based on the information it receives from the TC messages. An entry in the Topology 9

18 Information Base consists of an address of a potential destination which is the advertised neighbor from the MPR Selector Set in the received TC message, address of the last hop node to reach that destination which is the sender of the TC message and the sequence number of that corresponding MPR Selector Set [1]. Whenever a node receives a TC message, the following procedure is executed to record information in the Topology Information Base [3]: If the sender of TC message is not a symmetric 1-hop neighbor of node that receives the TC message, the TC message would be discarded. If there exist some entry in the Topology Information Base whose last hop node address is equal to the address of the sender of the TC message and the sequence number of the entry is greater than the sequence number of the received message, the TC message would be discarded. All the entries in the topology table whose last hop node address is equal to the address of the sender of the TC message and the sequence number of the entry is less than the sequence number of the received message, will be removed from the table. For each of the advertised neighbor from the MPR Selector Set in the TC message, if there exists an entry in the Topology Information Base such that the destination address is equal to advertised neighbor address, last hop node address is equal to the address of the sender of the TC message, then the holding time of that entry is increased. For each of the advertised neighbor from the MPR selector set in the TC message, if there does not exists any entry in the Topology Information Base such that the destination address is equal to advertised neighbor address, last hop node address is equal to the address of the sender of the TC message, then a new entry is inserted in the Topology Information Base. 2.6 Routing Table Calculation Every node in the network maintains a Routing Table which allows it to route data from it to every other node in the network. The Routing Table is calculated based on the information in Link Set, Neighbors Set, 2-hop Neighbor Set and Topology Information Base present at every node. If the entries in any of these sets change, the routing table would be recalculated. That is, the routing table will be recalculated when there is a change in the neighborhood concerning a bi-directional link or when a route to any destination is no longer valid because a corresponding topology entry is expired [1, 3]. The Topology Information Base stores information of connected pairs in the form (destination node, last hop node to reach the destination node). Routing Table is built from the information in Topology Information Base, by tracking the connected pairs in descending order. That is to find a route from source 10

19 X to destination Y, one has to find the connected pair (Intermediate node 1, Y), then connected pair (Intermediate node 2, Intermediate node 1), then connected pair (Intermediate node 3, Intermediate node 2), and this will continue one finds Intermediate node n in the 1-hop neighborhood of X. The entries in the routing table at every node consists of address of destination node for which a route is known, nexthop address to reach that destination and estimated distance in the form of number of hops to reach that destination [1]. The routing table can be calculated or recalculated using the below procedure [1]: All the existing entries of the routing table are removed First the routes to one-hop neighbor are recorded in the routing table with the destination address as the address of the node's one-hop neighbors. The next hop address for reaching these onehop neighbors would also be set to the address of the one-hop neighbors. The distance would be 1. Next the route entries for destination nodes that are n+1 hops away are recorded in the routing table starting from n = 1 and incrementing n by 1 each time until no new entry is to be recorded. For every entry in the Topology Information Base, if its destination address does not correspond to the destination address of an already existing route entry in the routing table and its last hop address corresponds to the destination address of an already existing route entry in the routing table with distance n, then a new entry is recorded in the routing table with address of destination node set to destination address in the Topology Information Base entry and the next hop is set to the next hop of the route entry whose destination address is equal to the above specified last hop address. The distance is set to n+1. After the entire routing table is calculated, the entries in the Topology Information Base, which have not been used in calculating the routes can be deleted as they may just provide multiple routes. 2.7 Soft State Signaling in OLSR Signaling system in all telecommunication networks can be broadly classified into two states: Soft- State signaling and Hard-State signaling. In Soft-State signaling, an installed state times out unless periodically refreshed by the receipt of a signaling message from the entity that initially installed the state indicating that the state should continue to remain installed. Soft state signaling does not require explicit state removal or a procedure to remove orphaned state should the state installer crash, as the unrefreshed state 11

20 eventually times out. In contrast, the Hard State signaling explicitly requires a state tear-down message from the state installer, otherwise the installed state continues to remain installed [22]. OLSR uses Soft-State approach to maintain consistency of the topology information and the routing tables amongst all the network nodes. Due to this, apart from the periodic control messages, the protocol does not generate any extra control traffic in response to nodes joining or leaving the network or due to link failures. Soft-state timers in OLSR are used for message generation and state maintenance. HELLO interval and TC interval are the message generation timers used in OLSR to send periodic HELLO and TC messages in the network. State maintenance timers like OLSR neighbor holding timer and OLSR TIB holding timer are used to keep updated information in the OLSR internal tables like Link Sets, Neighbor Sets and Topology Information Base. Obsolete and old entries are removed from these tables by timeout of these state maintenance timers [4]. In OLSR the default values of message generation and state maintenance timers are as below [23]: HELLO interval 2 Seconds TC interval 5 Seconds OLSR neighbor holding timer is set to 3 times the HELLO interval, which is 6 Seconds OLSR TIB holding timer is set to 3 times the TC interval, which is 15 Seconds Whenever new nodes join the network, a node detects its new neighbors and link states by periodically exchanging HELLO messages [4]. The HELLO messages are exchanged at regular intervals as specified in the HELLO interval timer. It means, the delay at a node, in learning about its neighborhood changes and link state changes depends on the frequency of exchanging HELLO messages. Similarly when a node leaves the network or the links between nodes go down, the corresponding entries in the Link Set and Neighbor Set will be removed after the state holding timer expires. TC messages are also exchanged periodically to help recover from loss of topology information caused by state corruption [4]. If the state holding timers are too long, then there would be delay in removing obsolete state information from the internal tables of OLSR, leading to broken/looped/no routes in the routing tables generated at every node. Therefore it is clear that the number of available valid routes in the routing table or the accuracy of the routing table generated at every node by the OLSR protocol depends on refresh intervals like HELLO interval and TC interval. 12

21 3. Implementation 3.1 Measuring Route Availability We are interested in measuring the route availability using the OLSR protocol with different refresh intervals. Availability of valid routes in a routing table depends on the number of Broken Routes in the routing tables Looped Routes in the routing tables No Routes in the routing tables Lesser the number of Broken Routes, Looped Routes and No Routes in the routing table, more the number of available valid routes. So first we need to understand which routes will be considered as Broken Routes, Looped Routes and No Routes Broken Routes A route is said to be broken, if somewhere along the path in the route there is a failed link due to change of neighbors, which the OLSR protocol did not detect immediately. Even if there is a single link failure in a route, the entire route is considered to be broken. Consider the route from source X to destination Y given in Figure 3.1 Figure 3.1: Route between source node X and destination node Y Suppose after some time, node N2 moves away from the neighborhood of Node N3 as shown in Figure 3.2. Then Node N2 is no longer within the transmission range of Node N3, causing a link failure between node N3 and node N2. 13

22 Figure 3.2: Broken Route between source node X and destination node Y Whenever the link connectivity between nodes in a network change, the routing protocols take time to detect the link failure and to re-establish a consistent view of the new topology. During this transient period, before the broken link between node N3 and node N2 is detected by the routing protocol, the older route X N3 N2 N1 Y, which is no longer valid remains in the routing table and data packets still get forwarded along this route leading to dropped packets. All such routes in the routing table with broken links will be counted as Broken Routes Looped Routes If the route specified in the routing table of a node is such that the path visits the same node more than once before reaching the destination node, then this leads to a Looped Route. Consider the route from source X to destination Y given in Figure 3.3 Figure 3.3: Looped Route between source node X and destination node Y In this route, the node N2 and N3 are visited more than once before reaching the destination, there by forming a loop. All such routes in the routing table which forms loops, will be counted as Looped Routes. 14

23 3.1.3 No Paths A route would be treated as No Path, if somewhere along the path there is a missing link. A link would be considered as missing, if there is no entry for it in the routing tables generated by the OLSR protocol. Consider the below routing tables: Routing Table entry for Node X: Destination Node Next Hop Node Distance Address of Node Y Address of Node N3 4 Routing Table entry for Node N3: Destination Node Next Hop Node Distance Address of Node Y Address of Node N2 3 Routing Table entry for Node N2: Destination Node Next Hop Node Distance Routing Table entry for Node N1: Destination Node Next Hop Node Distance Address of Node Y Address of Node Y 1 When source node X tries to find a route for Destination node Y, there would be a missing link from node N2. All such routes with missing links in the routing table will be considered as No Path Routes. 15

24 3.1.4 Available Routes Based on True Positions We want to treat a route between two nodes as Broken Route or No Path Route or Looped Route only if there actually exists a path between the two nodes. For this, based on the position coordinates of the nodes in the networks, we find the actual neighbors of every node at every instance of time and check if there exists a path between the nodes by implementing Dijkstra s algorithm using the actual neighbor information [19]. 3.2 Metrics Measured We use NS3 which is a simulation engine to conduct simulation experiments [12]. NS3 is an open source discrete-event network simulator which provides models of how packet data networks work and perform. NS3 uses the implementation of Optimized Link State Routing provided in [13]. The model simulated in NS3 is mostly compliant with OLSR as documented in RFC 3626 [3]. The behavior of OLSR can be modified by changing attributes or the macros in protocol source code [14, 23]. We use the Yans Wi-Fi Channel [15] model for setting up Wi-Fi connectivity between nodes for communication. This model implements the propagation model (IEEE ) described in Yet Another Network Simulator (yans) [16]. Each node is assigned a data rate of 11 Mbps for transferring data packets. We used the Constant Speed Propagation Delay Model and Range Propagation Loss Model. The MaxRange attribute in the Range Propagation Loss Model decides the maximum transmission range for every node [19]. The MaxRange values are set, such that the rate at which links change per node in the simulation is 0.3 or 0.5. The actual neighbors of every node at any given time is calculated on the basis of the actual position coordinates of the nodes and the MaxRange value. For a particular node, all the nodes positioned within the transmission range (MaxRange) of that node are considered to be its actual neighbors. We use the 2D random mobility model for setting up mobility within the nodes. In this model each node moves with a speed and direction chosen at random with the user provided random variables until a fixed amount of time or until a fixed distance has been walked. If the nodes hit the boundaries of the model which is specified by a rectangle, it rebounds on the boundary with a reflexive angle and speed [17]. We have set the mode which specifies the condition used to change the node's direction and speed to time and the time after which these changes occur to 2 seconds. That is after every 2 seconds, every node would change its direction and speed. The speed with which the nodes move is set to a random value between 2 m/s and 4m/s. The bound attribute fixes the boundaries for the area in which the nodes can move. This value is calculated based on the network size and propagation range and set accordingly. 16

25 A Random Rectangle Position Allocator model is used to allocate random positions for the nodes in the network within a rectangle according to a pair of random variables [18]. The X and Y attributes are same as the bounds used when setting up the 2D random mobility model. Simulation were run on different network sizes with nodes 25, 75, 100 and 125. For each network size, we varied the node densities. Node density refers to the number of nodes within the transmission range of that node. We used node densities of 4, 8, 12, 16 and 20. Simulations are run for 5 minutes. The initial set of observations for the first 2 minutes are discarded to allow the network reach a stable state before recording the observations. The output of the NS3 simulation is two text files. The first text file 'Routes' contains the routing tables generated at every node using the OLSR routing protocol. The other text file 'Neighbors' contains list of actual neighbors of every node based on the current positions of the nodes in the network. This data is recorded in the text files every 100 Milli Seconds. Figure 3.4: Initial position of nodes at the start of simulation 17

26 Figure 3.5: Snap shot of the simulation at time = 0.6 seconds Figure 3.6: Snap shot of the simulation at time = 6.75 seconds Figure 3.4 Figure 3.6 show the snap shots of simulations in NS3 at different time stamps. 18

27 We developed a python script to process the text files Routes and Neighbors to get the metrics which we are interested in studying. The output of the python script will be a text file having the below metrics: Time: It is the instance of time at which the other statistics are calculated. Simulation observations are recorded from 120 Seconds to 300 Seconds at every 100 Milli Seconds. Actual Paths: The 'Neighbors' file contains the list of actual neighbors of every node based on the current positions of the nodes at that instance of time. Using this information, we calculate total number of routes that exists from every node to all other nodes at every instance of time using Dijkstra's algorithm [19]. Broken Paths Ratio: The 'Routes' file is processed to check the validity of the routes specified in the routing tables maintained at every node using OLSR protocol. A route is said to be broken, if somewhere along the path in the route there is a failed link due to change of neighbors, which the OLSR protocol did not detect immediately. Routing tables in the 'Routes' file has information about the source node, destination node and the next hop node to reach the destination. While traversing a route from a source node to a destination node, we keep checking whether the next hop node in the routing table entry to reach that destination is the actual neighbor of the source node at that point of time or not. We can validate this using the actual neighbor list from the 'Neighbors' file. If the next hop node for a source node in the route is not its actual neighbor, we declare the route to be 'Broken'. Even if there is a single link failure in the route somewhere along the path, the entire route is considered to be broken. We count a route between two nodes as Broken Route only if there actually exists a path between the two nodes based on the current positions of the nodes at that instance of time. After we get the total number of Broken Routes that exists in the routing tables of all the nodes at every instance of time, we divide it with the total number of actual paths at that instance to get the Broken Paths Ratio. Looped Paths Ratio: If the route specified in the routing table of a node is such that the path visits the same node more than once before reaching the destination node, then this leads to a Looped Route. We count a route between two nodes as a Looped Route only if there actually exists a path between the two nodes based on the current positions of the nodes at that instance of time. We calculate the total number of Looped Routes present in the routing tables generated by OLSR at every instance of time and divide it with the total number of actual paths at that instance and get the Looped Paths Ratio. No Paths Ratio: A route in a routing table would be treated as a No Path if somewhere along the path there is a missing link. We count a route between two nodes as No Path Route only if there 19

28 actually exists a path between the two nodes based on the current positions of the nodes at that instance of time. We calculate the total number of No Path Routes present in the routing tables generated by OLSR at every instance of time and divide it with the total number of actual paths at that instance and get the No Paths Ratio. Valid Paths Ratio: All the routes in the routing table which are not broken or looped or no paths, will be considered as valid paths. To calculate the Valid Paths Ratio, we subtract the sum of Broken Path Ratio, Looped Path Ratio and No Path Ratio from 1. 20

29 4. Results and Observations We present the results and observations of the various simulations we ran in this section. Simulations were run for different values of HELLO interval (2 Seconds, 1 Seconds, 0.5 Seconds, 0.25 Seconds and 0.1 Seconds) and TC interval (5 Seconds, 2 Seconds, 1 Seconds, 0.5 Seconds and 0.25 Seconds). 4.1 Impact of varying HELLO Interval In this section we want to analyze the effect of varying HELLO interval alone, by keeping the TC interval fixed and see its impact on the number of Broken Paths, Looped paths, No Paths and Valid Paths. In all the charts plotted in this section, listed below are the notations used: N refers to network size that is number of nodes in the network D refers to the node density which defines the number of neighbors a node can have LC refers to the rate at which links change in the network HI is the HELLO interval used in the OLSR protocol TC is the TC interval used in the OLSR protocol The five line charts in Figure 4.1 Figure 4.5 show the Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio over the time from 120 seconds 300 seconds for different HELLO Intervals (2s, 1s, 0.5s, 0.25s, 0.1s) and TC Interval of 5s. The network consists of 100 nodes, with a node density of 8 and the rate of link changes per node in the network is around

30 Time Paths Ratio Time Paths Ratio Time BrokenPathsRatio LoopedPathsRatio NoPathsRatio ValidPathRatio Figure 4.1: Paths Ratio vs Time (N=100; D=8, LC=0.3, HI=2, TC=5) Time BrokenPathsRatio LoopedPathsRatio NoPathsRatio ValidPathRatio Figure 4.2: Paths Ratio vs Time (N=100; D=8, LC=0.3, HI=1, TC=5) 22

31 Time Paths Ratio Time Paths Ratio Time BrokenPathsRatio LoopedPathsRatio NoPathsRatio ValidPathRatio Figure 4.3: Paths Ratio vs Time (N=100; D=8, LC=0.3, HI=0.5, TC=5) Time BrokenPathsRatio LoopedPathsRatio NoPathsRatio ValidPathRatio Figure 4.4: Paths Ratio vs Time (N=100; D=8, LC=0.3, HI=0.25, TC=5) 23

32 Paths Ratio Time BrokenPathsRatio LoopedPathsRatio NoPathsRatio ValidPathRatio Figure 4.5: Paths Ratio vs Time (N=100; D=8, LC=0.3, HI=0.1, TC=5) We used box plots in Figure 4.6 Figure 4.9 to represent the range of Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio for different HELLO Intervals (2s, 1s, 0.5s, 0.25s, 0.1s) and TC Interval of 5s in box format, where the central mark is the median, the edges of the box are 25 th and 75 th percentile, the whiskers extend to the most extreme data points which are not considered outliers. Outliers are plotted individually beyond the whiskers. 24

33 Figure 4.6: Broken Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI Varying, TC = 5s) Figure 4.7: Looped Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI Varying, TC = 5s) 25

34 Figure 4.8: No Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI Varying, TC = 5s) Figure 4.9: Valid Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI Varying, TC = 5s) 26

35 Time Path Ratio From Figure 4.1 Figure 4.9, it is clear that when the HELLO interval is decreased from 2s to 0.1s, the Broken Paths Ratio decreases, Looped Paths Ratio increases and the No Path Ratio decreases first and then increases later. On the whole, it can be deduced that the Valid Paths Ratio increases with decreasing HELLO interval, because smaller the HELLO interval means HELLO messages are exchanged more frequently, thereby leading to lesser delays in identifying the link changes. For the same network size, node density, we now change the transmission range between the nodes such that rate of link changes per node is around 0.5. Figure 4.10 Figure 4.14 show the number of Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio over the time from 120 seconds 300 seconds for different HELLO Intervals (2s, 1s, 0.5s, 0.25s, and 0.1s) and TC Interval of 5s. Figure 4.15 Figure 4.18 represent the box plots that are plotted for Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio for different HELLO Intervals (2s, 1s, 0.5s, 0.25s, 0.1s) and TC Interval of 5s Time BrokenPathsRatio LoopedPathsRatio NoPathsRatio ValidPathRatio Figure 4.10: Paths Ratio vs Time (N=100; D=8, LC=0.5, HI=2, TC=5) 27

36 Time Paths Time Path Ratio Time BrokenPathsRatio LoopedPathsRatio NoPathsRatio ValidPathRatio Figure 4.11: Paths Ratio vs Time (N=100; D=8, LC=0.5, HI=1, TC=5) Time BrokenPathsRatio LoopedPathsRatio NoPathsRatio ValidPathsRatio Figure 4.12: Paths Ratio vs Time (N=100; D=8, LC=0.5, HI=0.5, TC=5) 28

37 Time Paths Ratio Time Paths Ratio Time BrokenPathsRatio LoopedPathsRatio NoPathsRatio ValidPathRatio Figure 4.13: Paths Ratio vs Time (N=100; D=8, LC=0.5, HI=O.25, TC=5) Time BrokenPathsRatio LoopedPathsRatio NoPathsRatio ValidPathRatio Figure 4.14: Paths Ratio vs Time (N=100; D=8, LC=0.5, HI=0.1, TC=5) 29

38 Figure 4.15: Broken Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.5, HI Varying, TC = 5s) Figure 4.16: Looped Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.5, HI Varying, TC = 5s) 30

39 Figure 4.17: No Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.5, HI Varying, TC = 5s) Figure 4.18: Valid Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.5, HI Varying, TC = 5s) 31

40 From Figure 4.10 Figure 4.18, we can see that even when the rate of link changes is increased from 0.3 to 0.5, the same trend is observed for Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio. That is, when the HELLO interval is decreased, Broken Paths Ratio decreases, Looped Paths Ratio increases and the No Path Ratio decreases first and then increases later, eventually increasing the Valid Paths Ratio in the routing tables Figure 4.19 Figure 4.22, show the box charts to compare the metrics across both the rates of link changes to see if the impact of refresh intervals on route availability changes due to difference in the rate of link changes. Figure 4.19: Broken Paths Ratio vs Refresh intervals (N=100; D=8, LC Varying, HI Varying, TC = 5s) 32

41 Figure 4.20: Looped Paths Ratio vs Refresh intervals (N=100; D=8, LC Varying, HI Varying, TC = 5s) Figure 4.21: No Paths Ratio vs Refresh intervals (N=100; D=8, LC Varying, HI Varying, TC = 5s) 33

42 Figure 4.22: Valid Paths Ratio vs Refresh intervals (N=100; D=8, LC Varying, HI Varying, TC = 5s) From Figure 4.19 Figure 4.22, we can say that the rate at which of link changes occur in a network does not have much impact on the Valid Paths Ratio when varying the refresh intervals like HELLO interval. That is the Valid Paths Ratio almost increases at the same rate for networks with rate of link changes as 0.3 or 0.5. The mean of Valid Path Ratio is slightly more in network with less rate of link changes. 4.2 Impact of varying TC Interval Now we want to analyze the effect of varying TC interval alone on the Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio, by keeping the HELLO interval fixed at 2s and 0.1s. The network consists of 100 nodes, with node density of 8 and the rate of link changes per node in the network is 0.3. Figure 4.23 Figure 4.26 show the plotted box plots for Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio for HELLO intervals (2s and 0.1s) and TC interval of 5s, 2s, 1s, 0.5s and 0.25s. 34

43 Figure 4.23: Broken Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI=2s and 0.1s, TC Varying) Figure 4.24: Looped Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI=2s and 0.1s, TC Varying) 35

44 Figure 4.25: No Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI=2s and 0.1s, TC Varying) Figure 4.26: Valid Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.3, HI=2s and 0.1s, TC Varying) 36

45 From Figure Figure 4.26, it is clearly visible that: When the HELLO interval is fixed to 2s and TC Interval is reduced from 5s to 0.25s, the Broken Paths Ratio decreases. However the Broken Paths Ratio decreases at a higher rate by reducing the HELLO interval from 2s to 0.1s, when compared to reducing the TC interval from 5s to 0.25s. When the HELLO interval is fixed to 0.1s and TC Interval is reduced from 5s to 0.25s, the Broken Paths Ratio almost remains the same. Looped Paths Ratio almost remain the same when the TC Interval is reduced from 5s to 0.25s. It slightly increases when we decrease the HELLO interval from 2s to 0.1s. When the HELLO interval is fixed to 2s and TC Interval is reduced from 5s to 0.25s, the No Paths Ratio increases at a high rate. It falls down when we decrease the HELLO interval from 2s to 0.1s. The Valid Paths Ratio almost remains the same when the HELLO interval is fixed to 2s or 0.1s and TC Interval is reduced from 5s to 0.25s. But they drastically increase when we decrease the HELLO interval from 2s to 0.1s. Therefore we can clearly say that the HELLO interval has more impact than TC interval on the Broken Paths Ratio and Valid Paths Ratio. Keeping the network size and node density same, when the rate of link changes in the network is changed to 0.5, the same behavior is observed (See Figure 4.27) with respect to changing the TC interval values. That is Valid Paths Ratio almost remain the same when the HELLO interval is fixed to 2s or 0.1s and TC Interval is reduced from 5s to 0.25s. But it drastically increases when we decrease the HELLO interval from 2s to 0.1s. 37

46 Figure 4.27: Valid Paths Ratio vs Refresh intervals (N=100; D=8, LC=0.5, HI=2s and 0.1s, TC Varying) 4.3 Impact of Refresh Intervals on Networks with Different Node Densities and Fixed Network size We want to analyze the effect of varying HELLO interval and TC interval on the Broken Paths Ratio, Looped paths Ratio, No Paths Ratio and Valid Paths Ratio, for a network of size 100 nodes with different node densities of 4, 8, 12, 16, and 20 and the rate of link changes per node in the network is 0.3 and 0.5. Figure 4.28 Figure 4.39 represent the box plots for Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio across 100 node networks with different densities for refresh intervals : HI = 2s TC = 5s; HI = 0.1s TC = 5s; HI = 0.1s TC = 0.25s; 38

47 Broken Paths: Figure 4.28: Broken Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.29: Broken Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=0.1s, TC=5s) 39

48 Figure 4.30: Broken Paths Ratio vs Node Densities (N=100, Varying Densities, LC=0.3 & 0.5,HI=0.1,TC=0.25) Looped Paths: Figure 4.31: Looped Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=2s, TC=5s) 40

49 Figure 4.32: Looped Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.33: Looped Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5,HI=0.1,TC=0.25) 41

50 No Paths: Figure 4.34: No Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.35: No Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=0.1s, TC=5s) 42

51 Figure 4.36: No Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=0.1, TC=0.25s) Valid Paths: Figure 4.37: Valid Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=2s, TC=5s) 43

52 Figure 4.38: Valid Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.39: Valid Paths Ratio vs Node Densities (N=100; Varying Densities, LC=0.3 & 0.5, HI=0.1, TC=0.25s) 44

53 From Figure 4.28 Figure 4.39, the following observations can be made: The Broken Paths Ratio has decreased for all node densities by reducing the HELLO interval. Reducing the TC interval, did not impact the Broken Paths Ratio much. The Broken Paths Ratio increased when node density was increased from 4 to 8 and when the node density was further increased from 8 to 20, the Broken Paths Ratio decreased. The same behavior can be seen for HI=2, TC=5; HI=0.1, TC=5; HI=0.1, TC=0.25. The Looped Paths Ratio increased slightly for all node densities by reducing the HELLO interval and TC interval. The Looped Paths Ratio increases when node density was increased from 4 to 8 and when the node density was further increased from 8 to 20, the Looped Paths Ratio almost decreased to 0. The No Paths Ratio decreases for low dense networks (D=4) with decreasing HELLO interval and TC interval. For high dense networks (D>=8), the No Paths Ratio slightly increases with decreasing HELLO interval and TC interval. The No Paths Ratio decreased when node density was increased from 4 to 20. For highly dense networks (node densities of 12, 16 and 20), the No Paths Ratio almost touched 0. The Valid Paths Ratio has increased for all node densities by reducing the HELLO interval. Reducing the TC interval, did not impact the Valid Paths Ratio much. The Valid Paths Ratio decreased when node density was increased from 4 to 8 and when the node density was further increased from 8 to 20, the Valid Paths Ratio kept increasing. At HI= 0.1s and TC = 5s, HI= 0.1s and TC = 0.25s, the Valid Paths Ratio for highly dense networks (node densities of 12, 16 and 20), almost ranged between 0.9 and Impact of HELLO Interval on Networks with Different Sizes and Fixed Node Densities We want to analyze the effect of varying HELLO interval (2s and 0.1s) on the Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio, for networks with different sizes of 50 nodes, 75 nodes, 100 nodes, 125 nodes. Networks with node densities of 4, 8, 12, 16, and 20 and the rate of link changes per node in the network is 0.3 and 0.5 will be used to analyze the metrics. TC interval is fixed at 5s For Node Density of 4 The Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio are plotted against networks with different node sizes for HELLO interval of 2s and 0.1s in Figure 4.40 Figure The node density in all the networks is maintained as 4. TC interval is fixed at 5s. 45

54 Broken Paths: Figure 4.40: Broken Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.41: Broken Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=0.1s, TC=5s) 46

55 Looped Paths: Figure 4.42: Looped Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.43: Looped Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=0.1s, TC=5s) 47

56 No Paths: Figure 4.44: No Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.45: No Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=0.1s, TC=5s) 48

57 Valid Paths: Figure 4.46: Valid Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.47: Valid Paths Ratio vs Network Sizes (Varying nodes, D=4, LC=0.3 & 0.5, HI=0.1s, TC=5s) 49

58 4.4.2 For Node Density of 8 The Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio are plotted against networks with different node sizes for HELLO interval of 2s and 0.1s in Figure 4.48 Figure The node density in all the networks is maintained as 8. TC interval is fixed at 5s. Broken Paths: Figure 4.48: Broken Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=2s, TC=5s) 50

59 Figure 4.49: Broken Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=0.1s, TC=5s) Looped Paths: Figure 4.50: Looped Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=2s, TC=5s) 51

60 Figure 4.51: Looped Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=0.1s, TC=5s) No Paths: Figure 4.52: No Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=2s, TC=5s) 52

61 Valid Paths: Figure 4.53: No Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=0.1s, TC=5s) Figure 4.54: Valid Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=2s, TC=5s) 53

62 Figure 4.55: Valid Paths Ratio vs Network Sizes (Varying nodes, D=8, LC=0.3 & 0.5, HI=0.1s, TC=5s) For Node Density of 12 The Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio are plotted against networks with different node sizes for HELLO interval of 2s and 0.1s in Figure 4.56 Figure The node density in all the networks is maintained as 12. TC interval is fixed at 5s.. 54

63 Broken Paths: Figure 4.56: Broken Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.57: Broken Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=0.1s, TC=5s) 55

64 Looped Paths: Figure 4.58: Looped Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.59: Looped Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=0.1s, TC=5s) 56

65 No Paths: Figure 4.60: No Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.61: No Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=0.1s, TC=5s) 57

66 Valid Paths: Figure 4.62: Valid Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.63: Valid Paths Ratio vs Network Sizes (Varying nodes, D=12, LC=0.3 & 0.5, HI=0.1s, TC=5s) 58

67 4.4.4 For Node Density of 16 The Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio are plotted against networks with different node sizes for HELLO interval of 2s and 0.1s in Figure 4.64 Figure The node density in all the networks is maintained as 16. TC interval is fixed at 5s. Broken Paths: Figure 4.64: Broken Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=2s, TC=5s) 59

68 Figure 4.65: Broken Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=0.1s, TC=5s) Looped Paths: Figure 4.66: Looped Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=2s, TC=5s) 60

69 Figure 4.67: Looped Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=0.1s, TC=5s) No Paths: Figure 4.68: No Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=2s, TC=5s) 61

70 Figure 4.69: No Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=0.1s, TC=5s) Valid Paths: Figure 4.70: Valid Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=2s, TC=5s) 62

71 Figure 4.71: Valid Paths Ratio vs Network Sizes (Varying nodes, D=16, LC=0.3 & 0.5, HI=0.1s, TC=5s) For Node Density of 20 The Broken Paths Ratio, Looped Paths Ratio, No Paths Ratio and Valid Paths Ratio are plotted against networks with different node sizes for HELLO interval of 2s and 0.1s in Figure 4.72 Figure The node density in all the networks is maintained as 20. TC interval is fixed at 5s. 63

72 Broken Paths: Figure 4.72: Broken Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.73: Broken Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=0.1s, TC=5s) 64

73 Looped Paths: Figure 4.74: Looped Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.75: Looped Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=0.1s, TC=5s) 65

74 No Paths: Figure 4.76: No Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.77: No Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=0.1s, TC=5s) 66

75 Valid Paths: Figure 4.78: Valid Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=2s, TC=5s) Figure 4.79: Valid Paths Ratio vs Network Sizes (Varying nodes, D=20, LC=0.3 & 0.5, HI=0.1s, TC=5s) 67

76 From Figure Figure 4.79, the following can be observed: The Broken Path Ratio decreases when decreasing the HELLO interval from 2s to 0.1s for all densities and network sizes. For dense networks (node density >= 8), the rate at which Broken Paths Ratio decreases when decreasing the HELLO interval is more for large networks. Also Broken Paths Ratio increases with increasing network size until 100 nodes and when network size increases from 100 nodes to 125 nodes, the Broken Paths Ratio slightly decreases. When HELLO interval is decreased from 2s to 0.1, the Valid Paths Ratio increases for all densities and network sizes. For dense networks (node density >= 8), the rate at which Valid Paths Ratio increases when decreasing the HELLO interval is more for large networks. Also for dense networks, the Valid Paths Ratio almost reaches 1 when HELLO interval is reduced from 2s to 0.1s. 4.5 Impact of Refresh Intervals on Network Utilization Now that it is clear from previous sections that availability of routes is impacted by changing the refresh intervals in Optimized Link State Routing protocol, we even want to analyze the network utilization when the refresh intervals are reduced. Figure 4.80 shows the number of available valid routes at different refresh intervals for a network of size 100 nodes, node density 10 and rate of link changes per node is 0.5. Figure 4.81 shows the network utilization throughout all the nodes in the network at different refresh intervals for the same network. Each nodes maximum data rate in the network is 11 Mbps. Because of interference and collisions, we assume each node gets at least 10% of its total capacity, that implies each node has a data rate of 1.1 Mbps for transferring data. 68

77 Figure 4.80: Valid Paths Ratio vs Varying Refresh Intervals Figure 4.81: Network Utilization by the nodes in a network for different refresh intervals 69