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<p>One of the most parts of VOIP management is fault management and, in having a good fault management, finding good mechanisms to detect faults in the network have to be considered.</p><p>The main focus of this project is to implement different types of fast fault recovery protocols in networks<strong>,</strong> especially networks that carry IP telephony. Having a complete understanding of some common link failure detection and fault recovery protocols<strong>,</strong> such as spanning tree protocol (STP), rapid spanning tree protocol (RSTP) and per-VLAN spanning tree protocol (PVSTP)<strong>,</strong> and also having a complete understanding of three other common techniques for fault detection and fault recovery, such as hot standby routing protocol (HSRP), virtual router redundancy protocol (VRRP) and gateway load balancing protocol (GLBP) will be regarded in the project. We are going to test some fault recovery protocols which can be used in IP telephony networks and choose the best. We intend to focus on this issue in LAN environment in theoretical descriptions and practical implementations.</p><p>The final outcome of the thesis is implementation in the Halmstad University’s lab environment to obtain the final result. For doing our thesis, we are going to use some technical tools as hardware tools (Cisco L3 and L2 switches, Routers, IP Phones) and tools which are used for network performance monitoring<strong>,</strong> like as CommVeiw.</p>

One of the most parts of VOIP management is fault management and, in having a good fault management, finding good mechanisms to detect faults in the network have to be considered. The main focus of this project is to implement different types of fast fault recovery protocols in networks, especially networks that carry IP telephony. Having a complete understanding of some common link failure detection and fault recovery protocols, such as spanning tree protocol (STP), rapid spanning tree protocol (RSTP) and per-VLAN spanning tree protocol (PVSTP), and also having a complete understanding of three other common techniques for fault detection and fault recovery, such as hot standby routing protocol (HSRP), virtual router redundancy protocol (VRRP) and gateway load balancing protocol (GLBP) will be regarded in the project. We are going to test some fault recovery protocols which can be used in IP telephony networks and choose the best. We intend to focus on this issue in LAN environment in theoretical descriptions and practical implementations. The final outcome of the thesis is implementation in the Halmstad University’s lab environment to obtain the final result. For doing our thesis, we are going to use some technical tools as hardware tools (Cisco L3 and L2 switches, Routers, IP Phones) and tools which are used for network performance monitoring, like as CommVeiw.

The focus of this study is to map, classify and analyse how different risk premia strategies that are fully implementable, perform and are affected by different economic environments. The results are of interest for practitioners who currently invest in or are thinking about investing in risk premia strategies. The study also makes a theoretical contribution since there currently is a lack of publicised work on this subject. A combination of the statistical methods cluster tree, spanning tree and principal component analysis are used to first categorise the investigated risk premia strategies into different clusters based on their correlation characteristics and secondly to find the strategies’ most important return drivers. Lastly, an analysis of how the clusters of strategies perform in different macroeconomic environments, here represented by inflation and growth, is conducted. The results show that the three most important drivers for the investigated risk premia strategies are a crisis factor, an equity directional factor and an interest rate factor. These three components explained about 18 percent, 14 percent and 10 percent of the variation in the data, respectively. The results also show that all four clusters, despite containing different types of risk premia strategies, experienced positive total returns during all macroeconomic phases sampled in this study. These results can be seen as indicative of a lower macroeconomic sensitivity among the risk premia strategies and more of an “alpha-like” behaviour. / Denna studie fokuserar på att kartlägga, klassificera och analysera hur riskpremie-strategier, som är fullt implementerbara, presterar och påverkas av olika makroekonomiska miljöer. Studiens resultat är av intresse för investerare som antingen redan investerar i riskpremiestrategier eller som funderar på att investera. Studien lämnar även ett teoretiskt bidrag eftersom det i dagsläget finns få publicerade verk som behandlar detta ämne. För att analysera strategierna har en kombination av de statistiska metoderna cluster tree, spanning  tree  och  principal  component  analysis  använts.  Detta  för  att  dels  kategorisera riskpremie-strategierna i olika kluster, baserat på deras inbördes korrelation, men också för att finna de faktorer som driver riskpremiestrategiernas avkastning. Slutligen har också en analys över hur de olika strategierna presterar under olika makroekonomiska miljöer genomförts där de makroekonomiska miljöerna representeras av inflation- och tillväxtindikatorer. Resultaten  visar  att  de  tre  viktigaste  faktorerna  som  driver  riskpremiestrategiernas avkastning  är  en  krisfaktor,  en  aktiemarknadsfaktor och  en  räntefaktor.  Dessa  tre  faktorer förklarar ungefär 18 procent, 14 procent och 10 procent av den undersökta datans totala varians. Resultaten  visar  också  att  alla  fyra  kluster,  trots  att  de  innehåller  olika  typer  av riskpremiestrategier,  genererade  positiv  avkastning  under  alla  makroekonmiska  faser  som studerades. Detta resultat ses som ett tecken på en lägre makroekonomisk känslighet bland riskpremiestrategier och mer av ett alfabeteende.

Network failures can originate from or be located in any one of several network layers as described by the OSI model. This investigation focuses on the role of physical topological design parameters in determining network reliability and performance as can be expected from the point of view of a typical client-server based connection in an Ethernet local area network. This type of host-to-host IP connection is found in many commercial, military and industrial network based systems. Using Markov modelling techniques reliability and performability models are developed for common network topologies based on the redundancy mechanism provided by IEEE spanning tree protocols. The models are tested and validated using the OPNET network simulation environment. The reliability and performability metrics calculated from the derived models for different topologies are compared leading to the following conclusions. The reliability of the entry-nodes into a redundant network is a determining factor in connection availability. Redundancy mechanisms must be extended from the entry-node to the connecting hosts to gain a significant benefit from redundant network topologies as network availability remains limited to three-nines. The hierarchical mesh network offers the highest availability (sevennines) and performability. Both these metrics can be accurately predicted irrespective of the position of the entry-node in the mesh. Ring networks offer high availability (five to sevennines) and performability if the ring remains small to medium sized, however for larger rings (N≥32) the availability is highly dependant on the relative position of the entry-node in the ring. Performability also degrades significantly as the ring size increases. Although star networks offer predictable and high performability the availability is low (four-nines) because of the lack of redundancy. The star should therefore not be used in IP networked systems requiring more than four-nines availability. In all the topologies investigated the reliability and performability can be increased significantly by introducing redundant links instead of single links interconnecting the various nodes, with the star topology availability increasing from four-nines to seven-nines and performance doubling. / MIng (Computer and Electronic Engineering), North-West University, Potchefstroom Campus, 2014

Network failures can originate from or be located in any one of several network layers as described by the OSI model. This investigation focuses on the role of physical topological design parameters in determining network reliability and performance as can be expected from the point of view of a typical client-server based connection in an Ethernet local area network. This type of host-to-host IP connection is found in many commercial, military and industrial network based systems. Using Markov modelling techniques reliability and performability models are developed for common network topologies based on the redundancy mechanism provided by IEEE spanning tree protocols. The models are tested and validated using the OPNET network simulation environment. The reliability and performability metrics calculated from the derived models for different topologies are compared leading to the following conclusions. The reliability of the entry-nodes into a redundant network is a determining factor in connection availability. Redundancy mechanisms must be extended from the entry-node to the connecting hosts to gain a significant benefit from redundant network topologies as network availability remains limited to three-nines. The hierarchical mesh network offers the highest availability (sevennines) and performability. Both these metrics can be accurately predicted irrespective of the position of the entry-node in the mesh. Ring networks offer high availability (five to sevennines) and performability if the ring remains small to medium sized, however for larger rings (N≥32) the availability is highly dependant on the relative position of the entry-node in the ring. Performability also degrades significantly as the ring size increases. Although star networks offer predictable and high performability the availability is low (four-nines) because of the lack of redundancy. The star should therefore not be used in IP networked systems requiring more than four-nines availability. In all the topologies investigated the reliability and performability can be increased significantly by introducing redundant links instead of single links interconnecting the various nodes, with the star topology availability increasing from four-nines to seven-nines and performance doubling. / MIng (Computer and Electronic Engineering), North-West University, Potchefstroom Campus, 2014

Spanning tree congestion was defined by Ostrovskii (2004) as a measure of how well a network can perform if only minimal connection can be maintained. We compute the parameter for several families of graphs. In particular, by partitioning a hypercube into pieces with almost optimal edge-boundaries, we give tight estimates of the parameter thereby disproving a conjecture of Hruska (2008). For a typical random graph, the parameter exhibits a zigzag behaviour reflecting the feature that it is not monotone in the number of edges. This motivates the study of the most congested graphs where we show that any graph is close to a graph with small congestion. Next, we enumerate independent sets. Using the independent set polynomial, we compute the extrema of averages in trees and graphs. Furthermore, we consider inverse problems among trees and resolve a conjecture of Wagner (2009). A result in a more general setting is also proved which answers a question of Alon, Haber and Krivelevich (2011). After briefly considering polynomial invariants of general graphs, we specialize into trees. Three levels of tree distinguishing power are exhibited. We show that polynomials which do not distinguish rooted trees define typically exponentially large equivalence classes. On the other hand, we prove that the rooted Ising polynomial distinguishes rooted trees and that the Negami polynomial determines the subtree polynomial, strengthening results of Bollobás and Riordan (2000) and Martin, Morin and Wagner (2008). The top level consists of the chromatic symmetric function and it is proved to be a complete invariant for caterpillars.

Nous nous intéressons aux lacets markoviens définis dans le cadre de la théorie des chaînes de Markov à temps continu sur un espace d'états discret. Ce sujet a notamment été étudié par Le Jan [LJ11] et Sznitman [Szn12]. En contraste avec ces références, nous ne supposerons pas la symétrie de la chaîne et nous intéresserons plutôt au cas infini. Tous les résultats sont présentés en termes de générateur de semi-groupe. En comparaison avec [LJ11], certaines preuves ont été détaillées ou améliorées.Nous fournissons par ailleurs quelques résultats sur les amas de boucles (voir [LJL12] dans le cas symétrique). Nous traitons notamment l'exemple du cercle discret. Nous étudions aussi les arbres couvrants définit par l'algorithme de Wilson dans le cas asymétrique.Dans la dernière partie, nous considérons la proportion des lacets couvrants l'espace. En utilisant la limite du spectre, nous donnons une expression générale de la limite de cette proportion pour une suite de graphes. Comme une application, nous donnons deux exemples concrets dans lesquels une transition de phase apparaît. / We are interested in Markov laces defined in the framework of the theory of Markov chains in continuous time on a discrete state space. This particular subject has been studied by Le Jan [LJ11] and Sznitman [Szn12]. In contrast to these references, we do not assume the reversibility of the chain and we are mostly interested in the case of countable state space. All the results are presented in terms of the generator of semigroup. In comparison with [LJ11], some demonstration has been detailed or improved.We also provide some results on the loop clusters (see [LJL12] in the reversible case). In particular, we study the example of discrete circle. We also study the spanning tree algorithm defined by Wilson in the non-symmetric case.In the last part, we consider the proportion of loops covering the whole space. Using the limit of the spectrums, we give a general expression for the limit of this ratio for a sequence of graphs. As an application, we give two examples in which a phase transition occurs.

O problema da árvore geradora de comunicação ótima recebe um grafo com comprimentos não negativos nas arestas e um requerimento não negativo entre cada par de vértices; sendo o objetivo encontrar uma árvore geradora do grafo que minimize o custo de comunicação, que é a soma sobre cada par de vértice da distância entre eles na árvore vezes o requerimento entre eles. Este problema é NP-difícil, assim como vários casos particulares dele. Neste trabalho estudamos algumas variantes deste problema, introduzimos novos casos particulares que são também NP-difíceis e propomos esquemas de aproximação polinomial para alguns deles. / The optimum communication spanning tree problem receives a graph with non-negative lengths over the edges and non-negative requirements for each pair of nodes; being the objective to find a spanning tree of the graph that minimizes the communication cost, which is given by the sum, over each pair of nodes, of the distance, in the tree, between the nodes multiplied by the requirement between them. This problem and several of its particular cases are NP-hard. In this work we study some of the variants, also we introduce new NP-hard particular cases of the problem and propose polynomial approximation schemes for some of them.