Doctor of Philosophy / Department of Electrical and Computer Engineering / Don M. Gruenbacher / Caterina M. Scoglio / As today's networks are no longer individual networks, networks are less robust towards failures and attacks. For example, computer networks and power networks are interdependent. Computer networks provide smart control for power networks, while power networks provide power supply. Localized network failures and attacks are amplified and exacerbated back and forth between two networks due to their interdependencies. This dissertation focuses on finding solutions to enhance network robustness. Software-defined networking provides a programmable architecture, which can dynamically adapt to any changes and can reduce the complexities of network traffic management. This architecture brings opportunities to enhance network robustness, for example, adapting to network changes, routing traffic bypassing malfunction devices, dropping malicious flows, etc. However, as SDN is rapidly proceeding from vision to reality, the SDN architecture itself might be exposed to some robustness threats. Especially, the SDN control plane is tremendously attractive to attackers, since it is the "brain" of entire networks. Thus, researching on network robustness helps protect network from a destructive disaster. In this dissertation, we first build a novel, realistic interdependent network framework to model cyber-physical networks. We allocate dependency links under a limited budget and evaluate network robustness. We further revise a network flow algorithm and find solutions to obtain a basic robust network structure. Extensive simulations on random networks and real networks show that our deployment method produces topologies that are more robust than the ones obtained by other deployment techniques. Second, we tackle middlebox chain problems using SDN. In computer networks, applications require traffic to sequence through multiple types of middleboxes to accomplish network functionality. Middlebox policies, numerous applications' requirements, and resource allocations complicate network management. Furthermore, middlebox failures can affect network robustness. We formulate a mixed-integer linear programming problem to achieve a network load-balancing objective in the context of middlebox policy chain routing. Our global routing approach manages network resources efficiently by simplifying candidate-path selections, balancing the entire network and using the simulated annealing algorithm. Moreover, in case of middlebox failures, we design a fast rerouting mechanism by exploiting the remaining link and middlebox resources locally. We implement proposed routing approaches on a Mininet testbed and evaluate experiments' scalability, assessing the effectiveness of the approaches. Third, we build an adversary model to describe in detail how to launch distributed denial of service (DDoS) attacks to overwhelm the SDN controller. Then we discuss possible defense mechanisms to protect the controller from DDoS attacks. We implement a successful DDoS attack and our defense mechanism on the Mininet testbed to demonstrate its feasibility in the real world. In summary, we vertically dive into enhancing network robustness by constructing a topological framework, making routing decisions, and protecting the SDN controller.

PhD Thesis / On congested North American urban road networks, driver concerns over increased travel time play a major role in whether or not cycling infrastructure is built. This fact is recognized by transportation planning agencies in Canada and the United States, including the Ministry of Transportation Ontario and the Federal Highway Administration. However, specific frameworks to address such driver concerns do not exist within the practice of urban planning nor the academic literature. One potentially fruitful avenue is to explore the methods and tools of critical link analysis. One such avenue is provided by the Network Robustness Index (NRI) and the Network Robustness Index Calculator, as this method and tool indexes critical links through traffic simulation from least to most critical. The specific information that can be used to address driver concerns is found in the least critical links as these roadways have additional capacity, and therefore may be considered underutilized. This thesis explores the use of the NRI as a framework for urban cycling infrastructure planning. Experiments on the utility of the NRI against common traffic and cycling planning tools are explored. The NRI Calculator’s ability to perform full network scans for potential bike lane locations, least cost corridors, and full cycling networks consisting of different designs is tested throughout the chapters of this manuscript. / Thesis / Doctor of Philosophy (PhD) / This thesis aids in the planning of urban bike lanes by addressing driver concerns through traffic simulation.

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Battery powered wireless sensors are widely used in industrial and regulatory monitoring applications. This is primarily due to the ease of installation and the ability to monitor areas that are difficult to access. Additionally, they can be left unattended for long periods of time. However, there are many challenges to successful deployments of wireless sensor networks (WSNs). In this thesis we draw attention to two major challenges. Firstly, with a view to extending network range, modern WSNs use mesh network topologies, where data is sent either directly or by relaying data from node-to-node en route to the central base station. The additional load of relaying other nodes’ data is expensive in terms of energy consumption, and depending on the routes taken some nodes may be heavily loaded. Hence, it is crucial to locate routes that achieve energy efficiency in the network and extend the time before the first node exhausts its battery, thus improving the network lifetime. Secondly, WSNs operate in a dynamic radio environment. With changing conditions, such as modified buildings or the passage of people, links may fail and data will be lost as a consequence. Therefore in addition to finding energy efficient routes, it is important to locate combinations of routes that are robust to the failure of radio links. Dealing with these challenges presents a routing optimisation problem with multiple objectives: find good routes to ensure energy efficiency, extend network lifetime and improve robustness. This is however an NP-hard problem, and thus polynomial time algorithms to solve this problem are unavailable. Therefore we propose hybrid evolutionary approaches to approximate the optimal trade-offs between these objectives. In our approach, we use novel search space pruning methods for network graphs, based on k-shortest paths, partially and edge disjoint paths, and graph reduction to combat the combinatorial explosion in search space size and consequently conduct rapid optimisation. The proposed methods can successfully approximate optimal Pareto fronts. The estimated fronts contain a wide range of robust and energy efficient routes. The fronts typically also include solutions with a network lifetime close to the optimal lifetime if the number of routes per nodes were unconstrained. These methods are demonstrated in a real network deployed at the Victoria & Albert Museum, London, UK.

Network downtime is costly for providers of information technology services. One cause of network downtime is link failures. The control plane of the network is the entity responsible for ensuring connectivity upon link failures. The data plane of the network forwards packets at line speed and it is controlled by the control plane. One disadvantage of ensuring connectivity at the control plane level is the time needed to react to a failure. The control plane is several orders of magnitude slower than the data plane. Moving the connectivity responsibility to the quicker data plane has therefore the potential to reduce network downtime. This work explored what level of connectivity robustness can be achieved when implementing data plane connectivity algorithms in today’s high-speed speed programmable switches. A literature study of several data plane connectivity algorithms was conducted. A critical aspect considered in this study was the simplicity of the data plane connectivity mechanism as high-speed programmable switches cannot support arbitrarily complex forwarding function. Data-Driven Connectivity (DDC) was selected as a suitable algorithm due to its high guaranteed connectivity and algorithmic simplicity. DDC was implemented in a virtual network environment using P4 programmable software switches. Our solution automates the generation of the virtual network based on a topology description. It also initializes the switches and generates the specific DDC P4 code for each switch. All the functions of DDC P4 have been tested to verify that each function behaved as expected. The path optimality of DDC P4 after several link failures were evaluated on the emulated Google’s wide area network topology, called B4 (2011). The path optimality evaluation shows that the path stretch of DDC P4, i.e., the gap from the shortest path in the number of hops, is not optimal for about 30% of the possible source/destination node pairs in the topology. The throughput of the DDC P4 was also evaluated along different number of link failures. The throughput results show a linear decrease in steps of 0.4 Mbps depending on which outbound link was utilized, starting from a throughput of 6.3 Mbps in the absence of failures. The current DDC P4 implementation does not scale well due to duplicate code for each destination in the topology. Both improving the scalability of the current implementation and an implementation on a hardware programmable switch remain as future work. / Avbrott i nätverket är kostsamt för leverantörer av informationsteknologitjänster. En orsak till avbrott är länkfel. Nätverkets textit kontrollplan är den entitet som ansvarar för att säkerställa anslutning vid länkfel. Nätverkets textit dataplan vidarebefordrar paket så snabbt som nätverkslänken klarar av, och det styrs av kontrollplanet. En nackdel med att säkerställa anslutning i kontrollplanet är den tid som krävs för att reagera på ett fel. Kontrollplanet är många gånger långsammare än dataplanet. Att flytta anslutningsansvaret till det snabbare dataplanet kan därför korta ner avbrotten i nätverket. Detta arbete undersökte vilken nivå av robusthet i anslutningsbarheten som kanuppnås vid implementering av algoritmer för anslutningsbarhet i dataplanet i dagens programmerbara höghastighetsswitchar. En litteraturstudie av flera dataplananslutningsalgoritmergenomfördes. En kritisk aspekt som beaktades i denna studie var enkelheten i dataplananslutningsmekanismen eftersom programmerbara höghastighetsswitchar inte kan stödja godtyckligt komplex vidarebefordringsfunktion. Datadriven anslutningsbarhet (DDC) valdes som en lämpligalgoritm på grund av dess höga garanterade anslutningsbarhet och algoritmiska enkelhet. DDC implementerades i en virtuell nätverksmiljö med P4-programmerbara mjukvaruswitchar. Vår lösning automatiserar genereringen av det virtuella nätverket baserat på en topologibeskrivning.Den initialiserar också switcharna och genererar den specifika DDC P4-koden för varje switch. Alla funktioner i DDC P4 har testats för att verifiera att varje funktion uppträdde som förväntat. Sökvägsoptimaliteten för DDC P4 efter flera länkfel utvärderades på Googles emulerade Wide Area Network (WAN), kallad B4 (2011). Bedömningen av sökvägsoptimaliteten visar att vägsträckningen för DDC P4, textit d.v.s., avståndet från den kortaste vägen i antalet hopp, inte är optimal för cirka 30 % av de möjliga ursprungs-/ destinationsnodparna i topologin. Genomströmningen av DDC P4 utvärderades också utifrån olika antal länkfel. Genomströmningsresultaten visar en linjär minskning i steg på 0,4 Mbps beroende på vilken utgående länk som användes, med utgångspunkt från en genomströmning på 6,3 Mbps vid frånvaro av fel. Den nuvarande DDC P4-implementeringen skalas inte bra på grund av duplicerad kod för varje destination i topologin. Både förbättring av skalbarheten för den nuvarande implementeringen och en implementering av en hårdvaruprogrammerbar switch kvarstår som framtida arbete.