ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California / Spectrum efficiency is the key challenge in modern telemetry systems. Network telemetry requires moving from a dedicated link structure to a network structure which is a very complex problem and requires spectrum management tools. A mixed network structure has been previously proposed for networked telemetry which employs a combination of cellular and Adhoc networks. Significant improvements in QoS and clustering of the complex aeronautical networks have been observed and published in several venues. However in the earlier work routing within the Ad-hoc clusters has not been addressed and the clustering has been done using an enhanced K-means clustering. In this paper, a well known clustering algorithm is adopted in the mixed network concept and clustering of the Ad-hoc nodes are optimized based on shortest route to the gateway and minimum hop count criteria. The proposed clustering technique in this paper leads to a jointly optimized cluster-topology and gateway-selection solution a complex aeronautical network. Simulation results towards the end of this paper illustrate that with the proposed method, cluster configuration is locally optimized and the best gateway for each cluster is successfully selected. With addition of traffic measures to the consideration in the routing, the proposed solution will leads to efficient spectrum allocation and improved QoS.

Opportunistic communication leverages communication opportunities arising by chance to provide significant performance benefit and even enable communication where it would be impossible otherwise. The goal of this dissertation is to optimize opportunistic communication to achieve good performance in wireless networks. A key challenge in optimizing opportunistic communication arises from dynamic and incidental nature of communication. Complicated wireless interference patterns, high mobility, and frequent fluctuations in wireless medium make the optimization even harder. This dissertation proposes a series of optimization frameworks that systematically optimizes opportunistic communication to achieve good performance in wireless mesh networks and vehicular networks. We make the following three major contributions: First, we develop novel algorithms, techniques, and protocols that optimize opportunistic communication of wireless mesh network to achieve good, predictable user performance. Our framework systematically optimizes end-to-end performance (e.g., total throughput). It yields significant improvement over existing routing schemes. We also show that it is robust against inaccuracy introduced by dynamic network conditions. Second, we propose a novel overlay framework to exploit inter-flow network coding in opportunistic routing. In this framework, an overlay network performs inter-flow coding to effectively reduce traffic imposed on the underlay network, and an underlay network uses optimized opportunistic routing to provide efficient and reliable overlay links. We show that inter-flow coding together with opportunistic routing and rate-limiting brings significant performance benefit. Finally, we develop a novel optimization framework in vehicular networks to effectively leverage opportunistic contacts between vehicles and access points (APs). We develop a new mobility prediction algorithm and an optimization algorithm to determine an efficient replication scheme that exploit the synergy among Internet connectivity, local wireless connectivity, mesh network connectivity, and vehicular relay connectivity. Based on our framework, we develop a practical system that enables high-bandwidth content distribution and demonstrate the effectiveness of our approach using simulation, emulation, and testbed experiments. / text

Στην εργασία αυτή, μελετήθηκε η δομή του σύγχρονου ίντερνετ από την σκοπιά του δικτύου και κατέστη σαφές το πως διασυνδέονται οι πάροχοι υπηρεσιών και οι τερματική χρήστες, πως γίνεται η δρομολόγηση και ποιοί αλγόριθμοι χρησιμοποιούνται για τιν επίτευξη της. / This diploma thesis focus on how modern networks connect together in order to create the internet and which algorithms used for the routing of informations that traverse through them.

Αντικείμενο της παρούσας διπλωματικής εργασίας αποτελεί η μελέτη της τηλεπικοινωνιακής κίνησης σε οπτικά δίκτυα δρομολόγησης μήκους κύματος. Στα πλαίσια της αποτίμησης της απόδοσής τους, υπολογίζεται η πιθανότητα φραγής κλήσης (Call Blocking Probability) για ένα σύνολο δοσμένων διαδρομών. Αφού αρχικά γίνεται αναφορά στην ιστορία και την εξέλιξη της τεχνολογίας των οπτικών ινών και των οπτικών δικτύων, το θέμα της εργασίας επικεντρώνεται στα οπτικά δίκτυα σταθερής δρομολόγησης και σταθερής εναλλακτικής δρομολόγησης. Γίνεται χρήση δύο αναλυτικών μοντέλων υπολογισμού της πιθανότητας απωλειών σε αυτά: το μοντέλο Birman και το μοντέλο Sridharan-Sivarajan, τα οποία υλοποιούνται στη γλώσσα προγραμματισμού C. Τα αποτελέσματα των μεθόδων ανάλυσης για συγκεκριμένα παραδείγματα συγκρίνονται με αυτά της προσομοίωσης, που υλοποιείται με χρήση της γλώσσας προσομοίωσης SIMSCRIPT II.5. Επιπρόσθετα, εξετάζεται η τεχνική της ομοιοκαταχώρησης τηλεπικοινωνιακής κίνησης (Traffic grooming) με προσομοίωση της λειτουργίας οπτικών δικτύων που κάνουν χρήση της τεχνικής αυτής. / The main objective of this diploma thesis is the study of the telecommunication traffic in Wavelength-Routed Optical Networks. In the frames of their performance evaluation, Call Blocking Probabilities for given routes are calculated. Firstly, the history and evolution of optical fibers and optical networks are described. Followingly, the present thesis is focused in Wavelength-Routed Optical Networks for two routing schemes: Fixed Routing and Fixed Alternate Routing. Two analytical models are used for the calculation of blocking probabilities for these optical networks: Birman model and Sridharan-Sivarajan model, which are realized in C programming language. Afterwards, both these analytical techniques and the simulation, which is realised in SIMSCRIPT II.5 simulation language, are applied in particular examples and their equivalent results are compared. In addition, the Traffic-Grooming technique is examined by simulating the operation of optical networks which use this specific technique.

Opportunistic spectrum access (OSA) promises to significantly improve the utilization of the RF spectrum. Under OSA, an unlicensed secondary user (SU) is allowed to detect and access under-utilized portions of the licensed spectrum, provided that such operation does not interfere with the communication of licensed primary users (PUs). Cognitive radio (CR) is a key enabling technology of OSA. In this dissertation, we propose several radio resource management and routing mechanisms that optimize the discovery and utilization of spectrum opportunities in a cognitive radio network (CRN). First, we propose a sequential channel sensing and probing mechanism that enables a resource-constrained SU to efficiently identify the optimal transmission opportunity from a pool of potentially usable channels. This mechanism maximizes the SUs expected throughput by accounting for the tradeoff between the reward and overhead of scanning additional channels. The optimal channel sensing and probing process is modeled as a maximum-rate-of-return problem in optimal stopping theory. Operational parameters, such as sensing and probing times, are optimized by exploiting the problem's special structure. Second, we study the problem of coordinated spectrum access in CRNs to maximize the CRNs throughput. By exploiting the geographic relationship between an SU and its surrounding PUs, we propose the novel concept of microscopic spectrum opportunity, in which active SUs and PUs are allowed to operate in the same region, subject to power constraints. Under this framework, we formulate the coordinated channel access problem as a joint power/rate control and channel assignment optimization problem. Centralized and distributed approximate algorithms are proposed to solve this problem efficiently. Compared with its macroscopic counterpart, we show that the microscopic-spectrum-opportunity framework offers significant throughput gains. Finally, at the network layer, we study the problem of truthful least-priced-path (LPP) routing for profit-driven CRNs. We design a route selection and pricing mechanism that guarantees truthful spectrum cost reporting from profit-driven SUs and that finds the cheapest route for end users. The problem is investigated with and without capacity constraints at individual nodes. In both cases, polynomial-time algorithms are developed to solve the LPP problem. Extensive simulations are conducted to verify the validity of the proposed mechanisms.

Transmission power control (TPC) has been used in wireless networks to improve channel reuse and/or reduce energy consumption. It has been mainly applied to single-input single-output (SISO) systems. Significant improvement in performancecan be achieved by employing multi-input multi-output (MIMO) techniques. In this dissertation, we propose adaptive medium-access control (MAC) protocols for power-controlled MIMO-capable wireless networks. In these protocols, we adapt the number of transmit/receive antennas, along with the transmission powers/rates, for the purpose of minimizing total energy consumption and/or maximizing network throughput. Our first protocol, called E-BASIC, exploits the diversity gain of MIMO by adapting the transmission mode, transmission power, and modulation order so as to minimize the total energy consumption. We incorporate E-BASIC in the design of an energy-efficient routing (EER) scheme that selects the least-energy end-to-end path. We then propose two MAC protocols that exploit the multiplexing gain of MIMO, and consider their integration into legacy systems. We alsopropose a combined energy/throughput MAC protocol, called CMAC, which dynamically switches between diversity and multiplexing modes so as to maximize a utility function that depends on both energy consumption and throughput. Finally, we consider employing "virtual" MIMO capability into single-antenna wireless sensor networks (WSNs). We propose a distributed MIMO-adaptive energy-efficient clustering/routing protocol, coined CMIMO, which aims at reducing energy consumption in multi-hop WSNs. In CMIMO, each cluster has up to two cluster heads (CHs), which are responsible for routing traffic between clusters. Simulation results indicate that our proposed protocols achieve significant energy/throughput improvement compared with non-adaptive protocols.

Wireless communication is a rapidly growing segment of the communication industry, with the potential to provide low-cost, high-quality, and high-speed information exchange between portable devices. To harvest the available bandwidth efficientlyin a wireless network, they employ multiple orthogonal channels over multiple ra-dios at the nodes. In addition, nodes in these networks employ directional antennasas radios to improve spatial throughput. This dissertation develops algorithms forrouting and broadcasting with channel assignment in such networks. First, we com-pute the minimum cost path between a given source-destination pair with channelassignment on each link in the path such that no two transmissions interfere witheach other. Such a path must satisfy the constraint that no two consecutive links onthe path are assigned the same channel, referred to as "channel discontinuity con-straint." To compute such a path, we develop two graph expansion techniques basedon minimum cost perfect matching and dijkstra's algorithm. Through extensive sim-ulations, we study the effectiveness of the routing algorithms developed based onthe two expansion techniques and the benefits of employing the minimum cost per-fect matching based solution. Secondly, we study the benefits of sharing channelbandwidth across multiple flows. We model the routing and channel assignmentproblem in two different ways to account for the presence and absence of inter-flowbandwidth sharing. Benefits of multiple paths between a source-destination pairmotivates the problem of computing multiple paths between a source-destinationpair with channel assignment such that all the paths can be active simultaneouslyto achieve maximal flow between the pair in the considered network. Since finding even two such paths is NP-hard, we formulate the problem as an integer linearprogram and develop efficient heuristic to find these paths iteratively. Thirdly, wecompute a broadcast tree from a given root with channel assignment such that all the links in the broadcast tree can be active simultaneously without interferingwith each other. Since finding such a tree is an NP-hard problem, we formulatethe problem as an integer linear program (ILP) and develop heuristics to find thebroadcast tree with channel assignment. We evaluate and compare the performanceof the developed heuristics with respect to their success rate, average depth of theobtained tree, and average path length from root to a node in the network. Thisdissertation also analyzes the blocking performance of a channel assignment schemein a multi-channel wireless line network. We assume that the existing calls in thenetwork may be rearranged on different channels to accommodate an incoming call.The analysis is limited to single-hop calls with different transmission ranges.Finally, this dissertation evaluates the performance of disjoint multipath routingapproaches for all-to-all routing in packet-switched networks with respect to packetoverhead, path lengths, and routing table size. We develop a novel approach basedon cycle-embedding to obtain two node-disjoint paths between all source-destinationpairs with reduced number of routing table entries maintained at a node (hence thereduced look up time), small average path lengths, and less packet overhead. Westudy the trade-off between the number of routing table entries maintained at anode and the average length of the two disjoint paths by: (a) formulating the cycle-embedding problem as an integer linear program; and (b) developing a heuristic.We show that the number of routing table entries at a node may be reduced toat most two per destination using cycle-embedding approach, if the length of thedisjoint paths are allowed to exceed the minimum by 25%.

Optical networks based on Wavelength Division Multiplexing (WDM) technology show many clear benefits in terms of high capacity, flexibility and low power consumption. All these benefits make WDM networks the preferred choice for today’s and future transports solutions which are strongly driven by a plethora of emerging online services. In such a scenario, capability to provide high capacity during the service provisioning phase is of course very important, but it is not the only requirement that plays a central role. Traffic dynamicity is another essential aspect to consider because in many scenarios, e.g., in the case of real time multimedia services, the connections are expected to be provisioned and torn down quickly and relatively frequently. High traffic dynamicity may put a strain on the network control and management operations (i.e., the overhead due to control message exchange can grow rapidly) that coordinate any provisioning mechanisms. Furthermore, survivability, in the presence of new failure scenarios that goes beyond the single failure assumption, is still of the utmost importance to minimize the network disruptions and data losses. In other words, protection against any possible future failure scenario where multiple faults may struck simultaneously, asks for highly reliable provisioning solutions. The above consideration have a general validity i.e., can be equally applied to any network segment and not just limited to the core part. So, we also address the problem of service provisioning in the access paradigm. Long reach Passive Optical Networks (PONs) are gaining popularity due to their cost, reach, and bandwidth advantages in the access region. In PON, the design of an efficient bandwidth sharing mechanism between multiple subscribers in the upstream direction is crucial. In addition, Long Reach PONs (LR-PONs) introduces additional challenges in terms of packet delay and network throughput, due to their extended reach. It becomes apparent that effective solutions to the connection provisioning problem in both the core and access optical networks with respect to the considerations made above can ensure a truly optimal end-to-end connectivity while making an efficient usage of resources. The first part of this thesis focuses on a control and management framework specifically designed for concurrent resource optimization in WDM-based optical networks in a highly dynamic traffic scenario. The framework and the proposed provisioning strategies are specifically designed with the objective of: (i) allowing for a reduction of the blocking probability and the control overhead in a Path Computation Element (PCE)-based network architecture, (ii)  optimizing resource utilization for a traffic scenario that require services with diverse survivability requirements which are achieved by means of  dedicated and shared path-protection, and (iii) designing provisioning mechanism that guarantees high connection availability levels in Double Link Failures (DLF) scenarios. The presented results show that the proposed dynamic provisioning approach can significantly improve the network blocking performance while making an efficient use of primary/backup resources whenever protection is required by the provisioned services. Furthermore, the proposed DLF schemes show good performance in terms of minimizing disruption periods, and allowing for enhanced network robustness when specific services require high connection availability levels. In the second part of this thesis, we propose efficient resource provisioning strategies for LR-PON. The objective is to optimize the bandwidth allocation in LR-PONs, in particular to: (i) identify the performance limitations associated with traditional (short reach) TDM-PON based Dynamic Bandwidth Allocation (DBA) algorithms when employed in long reach scenarios, and (ii) devise efficient DBA algorithms that can mitigate the performance limitations imposed by an extended reach. Our proposed schemes show noticeable performance gains when compared with conventional DBA algorithms for short-reach PON as well as specifically devised approaches for long reach. / <p>QC 20130520</p>

Complex Network Topologies (CNTs)–network holes and cuts–often occur in practical WSN deployments. Many researchers have acknowledged that CNTs adversely affect the performance of location-based routing and proposed various CNT- aware location-based routing protocols. However, although they aim to address practical issues caused by CNTs, many proposed protocols are either based on idealistic assumptions, require too much resources, or have poor performance. Additionally, proposed protocols are designed only for a single routing primitive–either unicast, multicast, or convergecast. However, as recent WSN applications require diverse traffic patterns, the need for an unified routing framework has ever increased. In this dissertation, we address these main weaknesses in the research on location- based routing. We first propose efficient algorithms for detecting and abstracting CNTs in the network. Using these algorithms, we present our CNT-aware location- based unicast routing protocol that achieves the guaranteed small path stretch with significantly reduced communication overhead. We then present our location-based multicast routing protocol that finds near optimal routing paths from a source node to multicast member nodes, with efficient mechanisms for controllable packet header size and energy-efficient recovery from packet losses. Our CNT-aware convergecast routing protocol improves the network lifetime by identifying network regions with concentrated network traffic and distributing the traffic by using the novel concept of virtual boundaries. Finally, we present the design and implementation details of our unified routing framework that seamlessly integrates proposed unicast, multicast, and convergecast routing protocols. Specifically, we discuss the issues regarding the implementation of our routing protocols on real hardware, and the design of the framework that significantly reduces the code and memory size to fit in a resource constrained sensor mote. We conclude with a proactive solution designed to cope with CNTs, where mobile nodes are used for “patching” CNTs to restore the network connectivity and to optimize the network performance.

This report presents an optimization of the allocation of maintenance resources for Air Navigation Service (ANS) equipment of which LFV is responsible for the maintenance. The purpose the authors have worked after is to research ways of minimizing travelling time linked to maintenance visits for ANS equipment, this report includes the suggestions where the maintenance facilities should be placed in order to minimize the total travelling time. The report describes the problem background and presents the customer, LFV. It includes a chapter on some of the theories used for facility location and routing, and also presents methods for reducing the total travelling time used for maintenance visits annually. The authors have worked with a given set of airports in Sweden. Information about the general work with maintenance as well as the annual demand of maintenance, including the frequency of visits, for each airport included in this project was received by Pär Oberger, the task expert and contact at LFV for this report. A model for facility location based on the p-median model have been created and used when solving the problem, it was written in AMPL and solved with the CPLEX solver. The model was modified with two additional constraints regulating the minimum annual working time and the maximum distance for one-way travelling. The authors deems that a solution with five facilities is better since the benefit of additional facilities, in term of lower total distance, do not compensate for the assumed cost of establishing them.