Routers (Computer networks)

In mobile ad hoc networks, it is challenging to solve the standard problems
encountered in fixed network because of the unpredictable motion of mobile nodes.
Due to the lack of a fixed infrastructure to serve as the backbone of the network, it
is difficult to manage nodes' locations and ensure the stable node performance. The
virtual mobile node (VMN) abstraction that has been applied implements an virtual
mobile node that consists of a set of real nodes traveling on one predetermined virtual
path to collect messages and deliver them to the destinations when they meet. It
conquers the unpredictable motion with virtual nodes' predictable motion. But it
encounters unavoidable failure when all the nodes leave the VMN region and stop
emulating the VMN. We extend the idea of the VMN abstraction to the Multi-path
Intelligent Virtual Mobile Node (MIVMN) abstraction, which allows the messages
to switch between multiple Hamiltonian paths to increase the message delivery ratio
and decrease the failure rate of the virtual nodes. Through simulation results we
show that the MIVMN abstraction successfully meets our goals.

Even though, the current cellular network provides the user with a wide array of
services, for a typical user voice communication is still the primary usage. It has become
increasingly important for a cellular network provider to provide the customers with the
clearest possible end-to-end speech during a call. However, this perceptually motivated
QoS is hard to measure. While the main goal of this research has been on the modeling of
the perceptual audio quality, this thesis focuses on the discovery of procedures for
collecting audio and diagnostic data, the evaluation of the captured audio, and the
mapping and visualization of the diagnostic and audio related data. The correct
application of these modified procedures should increase the productivity of the drive test
team as well as provides a platform for the accurate assessment of the data collected.

In a mobile ad hoc network, node cooperation in packet forwarding is required for the network to function properly. However, since nodes in this network usually have limited resources, some selfish nodes might intend not to forward packets to save resources for their own use. To discourage such behavior, we propose RMS, a reputation-based system, to detect selfish nodes and respond to them by showing that being cooperative will benefit there more than being selfish. We also detect, to some degree, nodes who forward only the necessary amount of packets to avoid being detected as selfish. We introduce the use of a state model to decide what we should do or respond to nodes in each state. In addition, we introduce the use of a timing period to control when the reputation should be updated and to use as a timeout for each state. The simulation results show that RMS can identify selfish nodes and punish them accordingly, which provide selfish nodes with an incentive to behave more cooperatively.

Innovation has flourished at the edge of the Internet; however, the core has experienced a slower pace of innovation. This lag is impacting the pace of innovation at the edge and threatening quality as ad hoc solutions are implemented to overcome core network barriers to innovation. Active networking technology, which opens up the architecture of routers, is proposed as a standard solution. Researchers draw an analogy to the computer industry where innovation is claimed to be accelerated by modularization. This argument is valid to the extent that the router market is similar to the computer market; however, contemporary innovation theories cast doubt on this likelihood. These theories indicate that for active networking technology to accelerate Internet innovation, extraordinary measures will be required to break the status quo. This paper analyzes this situation and makes recommendations, based on innovation theory, on how active networking can be successful in accelerating Internet innovation.

The ad hoc wireless network is an infrastructureless network, where mobile stations are typically powered by batteries. Energy conservation has therefore becomes a very important issue. In this thesis, we discuss our work on several problems in energy-efficient routing. Chapter 3 focuses on how to compute the minimum uniform broadcast transmission power in an ad hoc wireless network. Several algorithms are proposed and their running time compared through simulation. It is shown that Prim's Minimum Spanning Tree (MST) has better performance than Kruskal's MST and the two binary search algorithms. In the following two chapters, routing algorithms are studied for specific situations, when directional antenna is used (Chapter 4) or when partial signal could be collected, stored and integrated (Chapter 5). Different algorithms are discussed and their energy performance illustrated by simulation study. Their application and limitation are also discussed in the thesis.

This thesis describes QoS routing techniques in ad hoc networks. QoS routing is to find paths between given source and destinations that fulfill a set of QoS requirements. QoS routing in ad hoc networks is a challenging problem due to the dynamical nature of ad hoc networks and the complexity of the QoS routing problem. Ticket-based probing scheme (TBP) is a creative approach to solve QoS routing problem, however, its proactive nature makes it deficient and unscalable. In this thesis, we first present the adaptive ticket-based routing protocol (ATBR), a proactive protocol enhanced from TBP, by introducing a new imprecise QoS state model. We then present the location-aided, ticket-based routing protocol (LTBR), an integration of locate-based routing and ticket-based routing, where tickets are dynamically generated and guided by location and QoS metric. Our simulations show that, in networks under any density, LTBR achieves close performances to flooding with considerably lower routing overhead.

Disruption-Tolerant Networks (DTNs) are the networks comprised of a set of wireless nodes, and they experience unstable connectivity and frequent connection disruption because of the limitations of radio range, power, network density, device failure, and noise. DTNs are characterized by their lack of infrastructure, device limitation, and intermittent connectivity. Such characteristics make conventional wireless network routing protocols fail, as they are designed with the assumption the network stays connected. Thus, routing in DTNs becomes a challenging problem, due to the temporal scheduling element in a dynamic topology. One of the solutions is prediction-based, where nodes mobility is estimated with a history of observations. Then, the decision of forwarding messages during data delivery can be made with that predicted information. Current prediction-based routing protocols can be divided into two sub-categories in terms of that whether they are probability related: probabilistic and non-probabilistic. This dissertation focuses on the probabilistic prediction-based (PPB) routing schemes in DTNs. We find that most of these protocols are designed for a specified topology or scenario. So almost every protocol has some drawbacks when applied to a different scenario. Because every scenario has its own particular features, there could hardly exist a universal protocol which can suit all of the DTN scenarios. Based on the above motivation, we investigate and divide the current DTNs scenarios into three categories: Voronoi-based, landmark-based, and random moving DTNs. For each category, we design and implement a corresponding PPB routing protocol for either basic routing or a specified application with considering its unique features.

Controlling the cooperative behaviors of a fleet of autonomous underwater vehicles in a stochastic, complex environment is a formidable challenge in artificial intelligence. The complexity arises from the challenges of limited navigation and communication capabilities of underwater environment. A time critical cooperative operation by acoustic networks of Multiple Cooperative Vehicles (MCVs) necessitates a robust task allocation mechanism and an efficient path planning model. In this work, we present solutions to investigate two aspects of the cooperative schema for multiple underwater vehicles under realistic underwater acoustic communications: a Location-aided Task Allocation Framework (LAAF) algorithm for multi-target task assignment and a mathematical programming model, the Grid-based Multi-Objective Optimal Programming (GMOOP), for finding an optimal vehicle command decision given a set of objectives and constraints. We demonstrate that, the location-aided auction strategies perform significantly better than the generic auction algorithm in terms of effective task allocation time and information bandwidth requirements. In a typical task assignment scenario, the time needed in the LAAF algorithm is only a fraction compared to the generic auction algorithm. On the other hand; the GMOOP path planning technique provides a unique means for multi-objective tasks by cooperative agents with limited communication capabilities. Under different environmental settings, the GMOOP path planning technique is proved to provide a method with balance of sufficient expressive power and flexibility, and its solution algorithms tractable in terms of mission completion time, with a limited increase of overhead in acoustic communication. Prior to this work, existing multi-objective action selection methods were limited to robust networks where constant communication available.

Acoustic networks of autonomous underwater vehicles (AUVs) show great promise, but a lack of simulation tools and reliance on protocols originally developed for terrestrial radio networks has hindered progress. This work addresses both issues. A new simulator of underwater communication among AUVs provides accurate communication modeling and flexible vehicle behavior, while a new routing protocol, location-aware source routing (LASR) provides superior network performance. The new simulator was used to evaluate communication without networking, and then with networking using the coding or dynamic source routing (DSR) protocols. The results confirmed that a network was essential to ensure effective fleet-wide communication. The flooding protocol provided extremely reliable communication but with low message volumes. The DSR protocol, a popular routing protocol due to its effectiveness in terrestrial radio networks, proved to be a bad choice in an acoustic environment: in most cases, it suffered from both poor reliability and low message volumes. Due to the high acoustic latency, even moderate vehicle speeds caused the network topology to change faster than DSR could adapt. DSR's reliance on shortest-path routing also proved to be a significant disadvantage. Several DSR optimizations were also tested; most proved to be unhelpful or actually harmful in an underwater acoustic network. LASR was developed to address the problems noted in flooding and DSR. LASR was loosely derived from DSR, most significantly retaining source routes and the reply/request route discovery technique. However, LASR added features which proved, in simulation, to be significant advantages -- two of the most effective were a link/route metric and a node tracking system. To replace shortest-path routing, LASR used the expected transmission count (ETX) metric.