With the increase of mobile and smart device usage, the interest in dynamically forming networks is rising. One such type of network isWireless Mesh Networks (WMNs). WMNs are multi-hop networks, with a decentralised nature that can dynamically form into mesh topologies. Network Coding (NC) is a method that is used to increase the efficiency of networks by encoding and decoding data on packet level by means of an XOR operation. NC works well with WMNs because it can exploit WMNs broadcast and opportunistic listening properties. When implementing NC on WMNs the issue of security has to be taken into consideration. Dong et al. identified various security threats for intra-flow NC in WMNs. Intra-flow NC combines packets within individual flows, where the information is divided into different flows called generations, to optimize the decoding process. They identified threats for each component of intra-flow NC for WMNs. These components include forwarding node selection, data packet forwarding and acknowledgement delivery. These threats respectively for each component are wormhole attacks and link quality falsification, packet pollution and packet dropping and acknowledgementdropping, injection and delay. We identified that most security schemes focus on packet pollution attacks in NC, but not on any other threats. Packet dropping is also a major threat in networks that is not addressed. Both packet pollution and packet dropping are threats identified for the data forwarding component of WMNs. The Delayed Authentication with Random Transformations (DART) security scheme addresses packet pollution in intra-flow NC systems. The scheme is based on time asymmetry and checksums. The DART scheme only addresses packet pollution and not any of the other identified threats. The DART scheme was selected to be enhanced to also address packet dropping. To enhance the DART scheme we added additional information to the DART scheme’s checksum packets to detect malicious packet dropping nodes in the network. The information added to the checksum packet took the form of a HealthMatrix, which indicates how many packets a node has received and verified. The new scheme, called the Packet Dropping Detection (PDD) scheme collects the additional information from the checksum packets at the receiver node. The receiver sends the collected information to the source node which then uses the information to identify the malicious nodes in the network. These nodes are then removed from the network. The results show that this new scheme causes a small decrease in throughput – about 2%. The identification of malicious nodes can be used as a diagnostic tool and faulty nodes can be repaired or removed form the network. The advantage to detect malicious packet dropping nodes far outweighs this decrease in throughput. In this dissertation we investigate the effects of packet pollution and packet dropping on NC networks inWMNs. We also enhance an already existing scheme (DART) to add additional packet dropping detection security to it without a great loss in throughput. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013.

Design and management decisions require an accurate prediction of the performance of the network. Network performance estimation techniques require accurate network traffic models. In this thesis we are concerned with the modelling of network traffic for the wireless mesh network (WMN) environment. Queueing theory has been used in the past to model the WMN environment and we found in this study that queueing theory was used in two main methods to model WMNs. The first method is to consider each node in the network in terms of the number of hops it is away from the gateway. Each node is then considered as a queueing station and the parameters for the station is derived from the number of hops each node is away from the gateway. These topologies can be very limiting in terms of the number of physical topologies they can model due to the fact that their parameters are only dependent on the number of hop-counts each node is away from the gateway. The second method is to consider a fixed topology with no gateways. This method simplifies analysis but once again is very limiting. In this dissertation we propose a queueing based network traffic model that uses a connection matrix to define the topology of the network. We then derive the parameters for our model from the connection matrix. The connection matrix allows us to model a wider variety of topologies without modifying our model. We verify our model by comparing results from our model to results from a discrete event simulator and we validate our model by comparing results from our model to results from models previously proposed by other authors. By comparing results from our model to results of other models we show that our model is indeed capable of modelling a wider variety of topologies. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013.

With the increase of mobile and smart device usage, the interest in dynamically forming networks is rising. One such type of network isWireless Mesh Networks (WMNs). WMNs are multi-hop networks, with a decentralised nature that can dynamically form into mesh topologies. Network Coding (NC) is a method that is used to increase the efficiency of networks by encoding and decoding data on packet level by means of an XOR operation. NC works well with WMNs because it can exploit WMNs broadcast and opportunistic listening properties. When implementing NC on WMNs the issue of security has to be taken into consideration. Dong et al. identified various security threats for intra-flow NC in WMNs. Intra-flow NC combines packets within individual flows, where the information is divided into different flows called generations, to optimize the decoding process. They identified threats for each component of intra-flow NC for WMNs. These components include forwarding node selection, data packet forwarding and acknowledgement delivery. These threats respectively for each component are wormhole attacks and link quality falsification, packet pollution and packet dropping and acknowledgementdropping, injection and delay. We identified that most security schemes focus on packet pollution attacks in NC, but not on any other threats. Packet dropping is also a major threat in networks that is not addressed. Both packet pollution and packet dropping are threats identified for the data forwarding component of WMNs. The Delayed Authentication with Random Transformations (DART) security scheme addresses packet pollution in intra-flow NC systems. The scheme is based on time asymmetry and checksums. The DART scheme only addresses packet pollution and not any of the other identified threats. The DART scheme was selected to be enhanced to also address packet dropping. To enhance the DART scheme we added additional information to the DART scheme’s checksum packets to detect malicious packet dropping nodes in the network. The information added to the checksum packet took the form of a HealthMatrix, which indicates how many packets a node has received and verified. The new scheme, called the Packet Dropping Detection (PDD) scheme collects the additional information from the checksum packets at the receiver node. The receiver sends the collected information to the source node which then uses the information to identify the malicious nodes in the network. These nodes are then removed from the network. The results show that this new scheme causes a small decrease in throughput – about 2%. The identification of malicious nodes can be used as a diagnostic tool and faulty nodes can be repaired or removed form the network. The advantage to detect malicious packet dropping nodes far outweighs this decrease in throughput. In this dissertation we investigate the effects of packet pollution and packet dropping on NC networks inWMNs. We also enhance an already existing scheme (DART) to add additional packet dropping detection security to it without a great loss in throughput. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013.

Recent advances in methods to increase network utilization have lead to the introduction of a relatively new method called Network Coding. Network Coding is a method that can reduce local congestion in a network by combining information sent over the network. It is commonly researched in the information theory field after it was first introduced by Ahlswede et al in 2000. Network Coding was proven in 2003, by Koetter & Medard to be the only way to achieve the throughput capacity defined by the Min cut Max flow theorem of Shannon. It was applied deterministically in wired networks and randomly in wireless networks. Random Network Coding however requires a lot of overhead and may cause possible delays in the network. We found that there is an open question as to determine where in a wireless network, Network Coding can be implemented. In this thesis we propose to find opportunities for the implementation of Network Coding, by searching for known deterministic Network Coding topologies in larger Networks. Because a known topology is used, we will then also know how Network Coding should be implemented. This method of finding opportunities for the implementation of Network Coding using topology can be combined with a routing algorithm to improve the utilization of a wireless network. We implemented our method on three different topologies and searched 1000 random networks for the presence of these topologies. We found that these topologies occurred frequently enough to make our method a viable method of finding opportunities for the implementation of Network Coding. / Thesis (M.Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2009.

Infrastructure wireless mesh networks (IWMNs) provide inexpensive deployment, flexible extension of wireless infrastructure, and easy access to the Internet. With multiple radios at each node, a capacity per node improves by transmitting over these radios simultaneously using orthogonal channels. However, without properly addressing the problem of channel assignment and routing for those nodes that form wireless infrastructures, the resulting network throughput and reliability are unlikely to meet the requirements of those highly demanding, media distribution applications. On a particular channel, poor resource allocation at a given access point/gateway of the underlying IWMN can amplify the problem even further. Motivated by these problems, we develop, based on the theory of network coding, a set of alternative solutions that addresses the above issues. We first introduce a sub-optimal solution to the joint problem of network coding, channel assignment and link scheduling for throughput optimization in the multi-channel multi-radio IWMN. We mathematically formulate the problem as a linear program, taking into account opportunistic overhearing, among other constraints. Based on this formulation, we develop a sub-optimal, auction-based algorithm for network throughput optimization. Simulation results reveal the effectiveness of our algorithm in exploiting multiple radios and channels while coping with fairness issues arising from auctions. The proposed solution also shows promising gains over traditional routing solutions. Our experimental results on an 802.11 testbed further confirm these results. The second part of this thesis then presents three AP/gateway-oriented solutions that address the link-level issues related to radio resource allocation at a particular AP/gateway node of the underlying IWMN, which operates on a given channel serving a set of wireless clients. Since the last-hop wireless link is normally a bottleneck of the IWMN, the key idea underlying all the proposed solutions is to use a version of network coding at the bottlenecked AP/gateway. We use Markov chains and the probability theory to derive several performance measures related to media distribution for both uplink and downlink applications. Via extensive simulations, we show the promising delay and reliability gains of the network-coding based schemes over the traditional schemes without network coding.

Recent advances in methods to increase network utilization have lead to the introduction of a relatively new method called Network Coding. Network Coding is a method that can reduce local congestion in a network by combining information sent over the network. It is commonly researched in the information theory field after it was first introduced by Ahlswede et al in 2000. Network Coding was proven in 2003, by Koetter & Medard to be the only way to achieve the throughput capacity defined by the Min cut Max flow theorem of Shannon. It was applied deterministically in wired networks and randomly in wireless networks. Random Network Coding however requires a lot of overhead and may cause possible delays in the network. We found that there is an open question as to determine where in a wireless network, Network Coding can be implemented. In this thesis we propose to find opportunities for the implementation of Network Coding, by searching for known deterministic Network Coding topologies in larger Networks. Because a known topology is used, we will then also know how Network Coding should be implemented. This method of finding opportunities for the implementation of Network Coding using topology can be combined with a routing algorithm to improve the utilization of a wireless network. We implemented our method on three different topologies and searched 1000 random networks for the presence of these topologies. We found that these topologies occurred frequently enough to make our method a viable method of finding opportunities for the implementation of Network Coding. / Thesis (M.Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2009.

Channel assignment in wireless mesh network (WMN) aims at improving the network throughput by utilizing multiple orthogonal frequency channels to minimize the interference. Interference can be categorized as coordinated and non-coordinated, depending upon the relative location of the interfering links. Compared to coordinated interference, non-coordinated interference has a severe adverse impact on throughput. This thesis is based on the hypothesis that the network throughput can be improved significantly, if channel assignment minimizes non-coordinated interference with priority. We propose a static and centralized channel assignment scheme CCAS to show the effectiveness of the hypothesis. The cluster-based approach of CCAS minimizes non-coordinated interference with reduced complexity. CCAS improves the network throughput by upto 80%, compared to the existing schemes. We propose topology control scheme MATS that constructs low interference multipath network topology using a subset of links from physical topology. We report an additional improvement of upto 10% in the network throughput, when CCAS assigns channels to the links selected by MATS. In the final part of the thesis, we formulate generalized channel assignment as an optimization problem, accounting for real network traffic. The objective of the problem is to select the channels for links such that maximum incident traffic can be transmitted over the links, while ensuring a fair distribution of throughput amongst links and elimination of non-coordinated interference. For a given network and incident traffic, the solution to this problem generates the channel assignment resulting in optimal network throughput. We propose dynamic and distributed scheme LYCAS as an approximate solution to the problem. LYCAS employs MATS to construct network topology and cluster-based approach of CCAS to minimize non-coordinated interference. In addition, it periodically updates the assignment of channels to adapt to the changing traffic load. LYCAS achieves upto 68% of the optimal network throughput and upto 72% of optimal aggregate end-to-end throughput of multi-hop flows. It outperforms the existing schemes by a factor of 2.

Wireless mesh networks has rapid development over the last few years. However, due to properties such as distributed infrastructure and interference, which strongly affect the performance of wireless mesh networks, developing technology has to face the challenge of architecture and protocol design issues. Traditional layered protocols do not function efficiently in multi-hop wireless environments. To get deeper understanding on interaction of the layered protocols and optimize the performance of wireless mesh network, more recent researches are focusing on cross-layer measurement schemes and cross-layer protocol design. The goal of this project is to implement a distributed monitoring mechanism for IEEE802.11 based wireless mesh networks. This module is event-based and has modular structure that makes it flexible to be extended. This project results a novel Cross-Layer Monitoring Module, CLMM, which is a prototype that monitors each layer of the nodes locally and dynamically, calculates the average values of the metrics, compares these values with thresholds and handles the cross-layer messages of each node. The CLMM also has a routing module structure that can be extended to distribute the metrics to its neighbors.

Voice over IP (VoIP) traffic in a multi-hop wireless mesh network (WMN) suffers from a large overhead due to mac/IP/UDP/RTP headers and time collisions. A consequence of the large overhead is that only a small number of concurrent VoIP calls can be supported in a WMN[17]. Hop-to-hop packet aggregation can reduce network overhead and increase the capacity. Packet aggregation is a concept which combines several small packets, destined to a common next-hop destination, to one large packet. The goal of this thesis was to implement packet aggregation on a Linux distribution and to increase the number of concurrent VoIP calls. We use as testbed a two-hop WMN with a fixed data rate of 2Mbit/s. Traffic was generated between nodes using MGEN[20] to simulate VoIP behavior. The results from the tests show that the number of supported concurrent flows in the testbed is increased by 135% compared to unaggregated traffic.

The integrated Network Enhanced Telemetry (iNET) radios provide a two-way telemetry link that interconnects the airborne instrumentation system with ground-based systems. This capability brings the flight test telemetry domain into the realm of the more classic mesh networks in a mobile ad-hoc environment. The underlying radio frequency (RF) communication protocols defined in the iNET standards support a variety of classic networking protocols. The scheduling algorithms between Link Managers and radios can operate as a collision network, like classic Ethernet. This paper describes the communication protocols and scheduling algorithms of the iNET radios, and it provides results of their use in a self-scheduling algorithm such as a classical token ring network.