ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / The focus of this work is the development of a complete network architecture to enhance telemetry performance using a mobile base station (MBS). The present study proposes a means of enabling both the mobile ad-hoc network (MANET) and a cellular network to operate simultaneously within the same spectrum. In this paper the application of a modified k-means clustering to organize several hundred TAs in a complex network environment is presented. A mobile base station is added to the network to locate the congested area and support the network but positioning itself in the mixed network environment. A scenario with two base stations (one mobile and one stationary) is simulated and results are presented. It is observed that use of an additional mobile base station could greatly increase the quality of communication by providing uniform distribution of node traffic and interference across the clusters in a complex telemetry environment with several hundred TAs.

Mobile ad hoc networks create communication links without the aid of any infrastructure, forwarding packets among mobile nodes. The MANET research community has identified several fundamental challenges, among which the most prominent is discovering an optimal route between two nodes. Existing work has proposed a plethora of routing protocols. Since each protocol implements its own philosophy and algorithm to target a specific purpose, routing protocols in MANETs show very different characteristics. Selecting a particular protocol for an application or deployment environment involves evaluating many complex inter-dependent tradeoffs and can be an overwhelming task for an application designer. However, this decision can have a significant impact on the success of a system in terms of performance, cost, and responsiveness. Emerging distributed applications deployed in MANETs inherently experience highly dynamic situations, which necessitate real-time routing protocol selection in response to varying scenarios. Most of the relevant research in this area relies on simulation studies or empirical analysis to select a routing protocol, requiring an infeasible amount of time and resources for the approaches to be used in real-time decision making. In my dissertation work, I designed the Chameleon framework to facilitate real-time routing protocol decisions based on given application and environmental characteristics. My approach develops analytical models for important network layer performance measures capturing various inter-dependent factors that affect routing protocol behavior. I provide an analytical framework that expresses protocol performance metrics in terms of environment-, protocol-, and application-dependent parameters. This effort has resulted in detailed models for two important metrics: end-to-end delay and throughput. I specify detailed models for the parameters embedded in the models with respect to the ability of network deployers, protocol designers, and application developers to reasonably provide the information. Finally, in a systematic manner, I outline the Chameleon software framework to integrate the analytical models with parameters specified by these three groups of stakeholders. / text

Το βασικό χαρακτηριστικό των ασύρματων δικτύων αυθαίρετης τοπολογίας (wireless ad hoc networks) είναι πως δεν απαιτούν την ύπαρξη σταθερής υποδομής (σε αντίθεση π.χ. με τα κυψελωτά δίκτυα). Ένα ιδιαίτερα σημαντικό παράδειγμα τέτοιων δικτύων αποτελούν τα λεγόμενα δίκτυα αισθητήρων (sensor networks), τα οποία μπορούν να χρησιμοποιηθούν σε τομείς όπως η παρακολούθηση και καταγραφή φυσικών φαινομένων, ή η προσωρινή δημιουργία δικτύου επικοινωνίας σε περιοχές που έχουν πληγεί από κάποια καταστροφή, κλπ., και επομένως αποτελούν μια ερευνητική περιοχή μεγάλου ενδιαφέροντος. Στα δίκτυα αυτά, όταν ένας κόμβος πρέπει να στείλει ένα πακέτο σε κόμβο που βρίσκεται εκτός της ακτίνας μετάδοσης του, τότε η μετάδοση γίνεται μέσω κόμβων που βρίσκονται πάνω σε μια διαδρομή μεταξύ αυτών των δύο κόμβων. Επειδή, όμως, οι κόμβοι αυτοί συνήθως έχουν περιορισμένη ενέργεια, ο τρόπος δρομολόγησης είναι καθοριστικός για τη λειτουργία του δικτύου. Τα πρωτόκολλα δρομολόγησης βασίζονται σε διάφορες μεθόδους όπως: κάθε κόμβος να επικοινωνεί μόνο με ορισμένους από τους γείτονες του, ή κάθε κόμβος να επιλέγει κόμβους στους οποίους θα μεταδώσει πακέτα με βάση τη γεωμετρική θέση τους. Μια άλλη μέθοδος δρομολόγησης είναι η κατασκευή ενός εικονικού δικτύου υποδομής, οι κόμβοι του οποίου είναι κόμβοι του ασύρματου δικτύου και οι ακμές του οποίου χρησιμοποιούνται για τη μεταφορά των πακέτων. Η κατασκευή του δικτύου υποδομής πρέπει να πραγματοποιηθεί με κατανεμημένο τρόπο και το μέγεθος και η δομή του πρέπει να είναι τέτοια ώστε η δρομολόγηση να απαιτεί όσο το δυνατόν λιγότερη κατανάλωση ενέργειας από τους κόμβους. Στα πλαίσια της διπλωματικής αυτής εργασίας: 1) Αναπτύχθηκαν δύο νέες μέθοδοι δρομολόγησης σε ασύρματα δίκτυα αυθαίρετης τοπολογίας μέσω κατασκευής εικονικών δικτύων υποδομής. Οι μέθοδοι αυτοί βασίζονται σε αντίστοιχους αλγόριθμους κατασκευής επικαλυπτόντων υπογραφημάτων και έχουν την ιδιότητα ότι τα εικονικά δίκτυα που παράγονται έχουν σχετικά μικρό αριθμό ακμών, ενώ παράλληλα η απόσταση μεταξύ δύο κόμβων στο εικονικό δίκτυο είναι το πολύ t φορές μεγαλύτερη από την ελάχιστη απόσταση τους στο αρχικό δίκτυο (όπου t είναι παράμετρος που εξαρτάται από τον αλγόριθμο). 2) Υλοποιήθηκαν οι δύο αυτές νέες μέθοδοι δρομολόγησης σε κατάλληλο περιβάλλον εξομοίωσης και έγινε εκτενής πειραματική αξιολόγηση τους. / The characteristic feature of wireless ad hoc networks is that there is no fixed infastructure (in constrast with cellular networks). One considerabe example of such networks is sensor networks, which can be used to monitor a natural phenomenon, or to construct a temporary communication network in areas where a disaster has occurred, etc, therefore wireless ad hoc networks is a research area of great interest. In wireless ad hoc networks when a node needs to send a message to a node which relies outside of its transmission range, then the transmission takes place through the nodes which rely on a path which connects these two nodes. The wireless nodes, however, have limited energy, therefore routing method is crusial for the operation of the network. Routing protocols are based on several methods, such as: each node is allowed to communicate with only a selected subset of its neighbors, or each node chooses to transmits a message to one of its neighbors based on its geometrical position. Another routing method is to construct a virtual backbone network. The virtual network has the same nodes as the ad hoc network, but only its links are used for the routing of messages. The construction of the virtual network must be executed in a distributed way and its size and structure must be suitable to allow the nodes to consume as less energy as possible in order to support the routing protocol. In this work 1) we have developed two new routing methods for wireless ad hoc networks by constructing virtual networks. These two methods are based on corresponding algorithms for maintaining spanners. The virtual networks constructed have relatively small number of links, while having the ability that for every pair of nodes their distance in the virtual network is at most t times their distance in the ad hoc network (parameter t depends on the algorithm). 2) we have implemented these two algorithms in a simulation environment, and we have conducted an extensive study on them.

Η διπλωματική αυτή σκοπό έχει να μελετήσει στρατηγικές οι οποίες έχουν ως στόχο την αύξηση της αποδοτικότητας με κριτήριο την ενέργεια σε ad hoc δίκτυα. Σε αυτού του είδους τα δίκτυα η ενέργεια είναι κρίσιμος πόρος και η εξοικονόμησή της είναι κρίσιμος παράγοντας. Θα ακολουθήσουμε τον αλγόριθμο δρομολόγησης multi-cost με cost vectors πολλών παραμέτρων. Με βάση αυτά τα cost vectors ένα σύνολο από candidate paths θα υπολογιστούν για κάθε ζευγάρι κόμβων source-destination και μια συνάρτηση βελτιστοποίησης χρησιμοποιείται για να επιλεχθεί το βέλτιστο από αυτά. Οι παράμετροι που μας ενδιαφέρουν είναι ο αριθμός των hops σε ένα μονοπάτι, η υπολειπόμενη ενέργεια και η ισχύς μετάδοσης των κόμβων σε ένα μονοπάτι καθώς και η παρεμβολή που δημιουργείται από την μετάδοση ενός κόμβου. Αυτές οι παράμετροι συνδυάζονται σε ποικίλες συναρτήσεις βελτιστοποίησης οι οποίες αντιστοιχούν σε διαφορετικούς αλγόριθμους δρομολόγησης και οι οποίοι εξετάζονται για την επιλογή του βέλτιστου μονοπατιού. Λαμβάνοντας υπόψη όλες αυτές τις συναρτήσεις εξετάζουμε την συμπεριφορά του δικτύου προσέχοντας την κατανάλωση ενέργειας, το throughput κα. Από τα πειράματα καταλήγουμε στις βέλτιστες από τις συναρτήσεις βελτιστοποίησης. / In this work we study the combination of multi-cost routing and variable transmission power in wireless ad hoc networks. We assume that the nodes have power control capabilities and can adjust their transmission power to their desired level. We propose algorithms for selecting the routes to be followed by the packets and the transmission power to be used by the nodes at each hop in order to reduce interference and energy consumption, and improve network performance. The cost parameters used by the proposed interference/energy-aware routing algorithms are the number of hops of the paths, the interference caused to other nodes, the node residual energies, and the node transmission powers. In the experiments conducted we examine the resulting network performance with respect to energy consumption, packet delay, frequency of collisions, and other parameters of interest. Our results show that the proposed routing algorithms significantly improve network performance and lifetime.

With the growth of Internet, the underlying protocols are increasingly challenged by new technologies and applications. The original Internet protocols were, however, not designed for wireless communication, mobility, long disconnection times, and varying bandwidths. In this thesis, we study challenged networking, and how well old and new protocols operate under such constraints. Our study is experimental. We build network testbeds and measure the performance of alternative protocols and architectures. We develop novel methodologies for repeatable experiments that combine emulations, simulations and real world experiments. Based on our results we suggest modifications to existing protocols, and we also develop a new network architecture that matches the constraints of a challenged network, in our case, an opportunistic network. One of our most important contributions is an Ad hoc Protocol Evaluation (APE) testbed. It has been successfully used worldwide. The key to its success is that it significantly lowers the barrier to repeatable experiments involving wireless and mobile computing devices. Using APE, we present side-by-side performance comparisons of IETF MANET routing protocols. A somewhat surprising result is that some ad hoc routing protocols perform a factor 10 worse in the testbed than predicted by a common simulation tool (ns-2). We find that this discrepancy is mainly related to the protocols’ sensing abilities, e.g., how accurately they can infer their neighborhood in a real radio environment. We propose and implement improvements to these protocols based on the results. Our novel network architecture Haggle is another important contribution. It is based on content addressing and searching. Mobile devices in opportunistic networks exchange content whenever they detect each other. We suggest that the exchange should be based on interests and searches, rather than on destination names and addresses. We argue that content binding should be done late in challenged networks, something which our search approach supports well.

Mobile ad hoc networks (MANETs) are generating much interest both in academia and the telecommunication industries. The principal attractions of MANETs are related to the ease with which they can be deployed due to their infrastructure-less and decentralized nature. For example, unlike other wireless networks, MANETs do not require centralized infrastructures such as base stations, and they are arguably more robust due to their avoidance of single point of failures. Interestingly, the attributes that make MANETs attractive as a network paradigm are the same phenomena that compound the challenge of designing adequate security schemes for these innovative networks. / One of the challenging security problems is the issue of certificate revocation in MANETs where there are no on-line access to trusted authorities. In wired network environments, when certificates are to be revoked, certificate authorities (CAs) add the information regarding the certificates in question to certificate revocation lists (CRLs) and post the CRLs on accessible repositories or distribute them to relevant entities. In purely ad hoc networks, there are typically no access to centralized repositories or trusted authorities; therefore the conventional method of certificate revocation is not applicable. / Another challenging MANET security problem is the issue of secure routing in the presence of selfish or adversarial entities which selectively drop packets they agreed to forward; and in so doing these selfish or adversarial entities can disrupt the network traffic and cause various communication problems. / In this thesis, we present two security protocols we developed for addressing the above-mentioned MANET security needs. The first protocol is a decentralized certificate revocation scheme which allows the nodes within a MANET to have full control over the process of certificate revocation. The scheme is fully contained and it does not rely on any input from centralized or external entities such as trusted CAs. The second protocol is a secure MANET routing scheme we named Robust Source Routing (RSR). In addition to providing data origin authentication services and integrity checks, RSR is able to mitigate against intelligent, colluding malicious agents which selectively drop or modify packets they are required to forward.

The central focus of this dissertation is mobile ad hoc networks (MANETs) and their security. MANETs are autonomous networks of wireless nodes connected in an ad hoc manner, and have unique characteristics that make them difficult to secure. The principal aims of this investigation are to discuss the research and evaluation of existing mechanisms to secure MANETs and to design the implementation of a unique security mechanism. Key management is a major challenge in these networks due to the lack of fixed network infrastructure. In presenting a survey of the existing key management solutions for MANETs, the findings indicate that most security attacks target the network layer and more specifically the routing protocol. Consequently, the provision of secure routes is a vital element for trust establishment, and accordingly a survey is provided of the existing secure ad hoc routing protocols. The observation is made that most secure ad hoc routing protocols assume the existence of a key management system to certify, authenticate, and distribute keying information. Mobile ad hoc networks cannot assume the existence of a centralized authority member to perform key management tasks, and the problem of key management must be addressed. A novel key management solution called Direct Indirect Trust Distribution (DITD) is proposed for an on-demand ad hoc routing protocol. The solution includes a trust evaluation mechanism and a key distribution scheme to distribute keying information in the form of certificates. The key distribution scheme performs localized certificate exchanges following the routing procedure. A security evaluation metric is proposed that aggregates trust along a path based on a security metric and the path distance. The proposed solution is implemented on a modified AODV routing protocol, and simulated on the ns2 Network Simulator. Simulations are conducted in order to compare the performance of the AODV and DITD protocols. The simulation results show that the DITD model provides key distribution and trust path selection with minimal effect on the routing agent. The findings of the investigation confirm that DITD can be used as a basis for the operation of existing security protocols requiring a secure key distribution mechanism. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

Vehicular Ad hoc Networks (VANET) exhibit highly dynamic behavior with high mobility and random network topologies. The performance of Transmission Control Protocols in such wireless ad hoc networks is plagued by a number of problems: frequent link failures, scalability, multi-hop data transmission and data loss. To address these VANET routing issues, I have used the ideas from swarm intelligence. The Ant Colony Optimization (ACO), which is a branch of swarm intelligence, is the main source of my inspiration. I have designed an ant-based routing algorithm which addresses routing issues prevalent in VANETs: adaptivity, robustness and scalability. One attractive feature of ACO is that they provide multiple routes from source to destination, resulting in more robust network. In this work, together with ACO, I have used the ideas from zone routing protocols to develop my algorithm: Mobility Aware Zone based Ant Colony Optimization Routing for VANET that exhibits locality and scalability.

The continual growth of computing power in small devices has motivated the development of novel approaches to optimizing operational systems efficiently and effectively. These optimization problems are often so complex that solving them analytically may be difficult, if not prohibited. One method for solving such problems is to use online simulation. However, challenges in using online simulation include the issues of responsiveness (e.g., because of communication delays), scalability, and failure resistance. To tackle these issues, this study proposes embedding online simulations into a network of sensors that monitors the system under investigation. This thesis explores an approach termed “ad hoc distributed simulation,” which is based on embedding online simulations into a sensor network and adding communication and synchronization among simulators to model operational systems. This approach offers several potential advantages over existing approaches: (1) it can provide rapid response to system dynamics as well as efficiency since data exchange is local to the sensor network, (2) it can achieve better scalability to incorporate more sensors, and (3) it can provide better robustness to failures because portions of the system are still under local control. This research addresses several statistical issues in this ad hoc approach: (1) rapid and effective estimation of the input processes at model boundaries, (2) estimation of system-wide performance measures from individual simulator outputs, and (3) correction mechanisms responding to unexpected events or inaccuracies within the model. This thesis examines ad hoc distributed simulation analytically and experimentally, mainly focusing on the accuracy of predicting the performance of open queueing networks. First, the analytical part formalizes the ad hoc approach and evaluates its accuracy at modeling certain class of open queueing networks with regard to the steady-state system performance measures. This work concerning steady-state metrics is extended to a broader class of networks by an empirical study, which presents evidence to show that the ad hoc approach can generate predictions comparable to those from sequential simulations. Furthermore, a “buffered-area” mechanism is proposed to substantially reduce prediction bias with a moderate increase in execution time. In addition to those steady-state studies, another empirical study targets the prediction accuracy of the ad hoc approach at open queueing networks with short-term system-state transients. This study demonstrates that, with slight modification to the prior design of the ad hoc queueing simulation method for those steady-state studies, system dynamics can be well modeled. The results, again, support the conclusion that the ad hoc approach is competitive to the sequential simulation method in terms of prediction accuracy.

In wireless networks, devices (nodes) are connected by wireless links. An important issue is to set up high quality (high bandwidth) and efficient routing paths when one node wants to send packets to other nodes. Resource allocation is the foundation to guarantee high quality connections. In addition, it is critical to handle void areas in order to set up detour-free paths. Moreover, fast message broadcasting is essential in mobile wireless networks. Thus, my research includes dynamic channel allocation in wireless mesh networks, geographic routing in Ad Hoc networks, and message broadcasting in vehicular networks. The quality of connections in a wireless mesh network can be improved by equip- ping mesh nodes with multi-radios capable of tuning to non-overlapping channels. The essential problem is how to allocate channels to these multi-radio nodes. We develop a new bipartite-graph based channel allocation algorithm, which can improve bandwidth utilization and lower the possibility of starvation. Geographic routing in Ad Hoc networks is scalable and normally loop-free. However, traditional routing protocols often result in long detour paths when holes exist. We propose a routing protocol-Intermediate Target based Geographic Routing (ITGR) to solve this problem. The novelty is that a single forwarding path can be used to reduce the lengths of many future routing paths. We also develop a protocol called Hole Detection and Adaptive Geographic Routing, which identifies the holes efficiently by comparing the length of a routing path with the Euclidean distance between a pair of nodes. We then set up the shortest path based on it. Vehicles play an important role in our daily life. During inter-vehicle communication, it is essential that emergency information can be broadcast to surrounding vehicles quickly. We devise an approach that can find the best re-broadcasting node and propagate the message as fast as possible.