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. / This allowed LASR to make more informed routing decisions which greatly increased performance compared to DSR. The node tracking system was the most novel addition: using only implicit communication coupled with the use of time-division multiple access (TDMA), the tracking system provided predicted node locations. These predictions made it possible for LASR to proactively respond to topology changes. In most cases, LASR outperformed flooding and DSR in message delivery reliability and message delivery volume. / by Edward A. Carlson. / Thesis (Ph.D.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

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. / The dynamic task allocation, together with the GMOOP path planning controller, provides a comprehensive solution to the search-classify tasks for cooperative AUVs. / by Yueyue Deng. / Thesis (Ph.D.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Previous research on ECN and RED usually considered only a limited traffic domain, focusing on networks with a small number of homogeneous flows. The behavior of RED and ECN congestion control mechanisms in TCP network with many competing heterogeneous flows in the bottleneck link, hasn't been sufficiently explored. This thesis first investigates the behavior and performance of RED with ECN congestion control mechanisms with many heterogeneous TCP Reno flows using the network simulation tool, ns-2. By comparing the simulated performance of RED and ECN routers, this study finds that ECN does provide better goodput and fairness than RED for heterogeneous flows. However, when the demand is held constant, the number of flows generating the demand has a negative effect on performance. Meanwhile, the simulations with many flows demonstrate that the bottleneck router's marking probability must be aggressively increased to provide good ECN performance. Based on these simulation results, an Adaptive ECN algorithm (AECN) was studied to further improve the goodput and fairness of ECN. AECN divides all flows competing for a bottleneck into three flow groups, and deploys a different max for each flow group. Meanwhile, AECN also adjusts min for the robust flow group and max to get higher performance when the number of flows grows large. Furthermore, AECN uses mark-front strategy, instead of mark-tail strategy in standard ECN. A series of AECN simulations were run in ns-2. The simulations show clearly that AECN treats each flow fairer than ECN with the two fairness measurements: Jain's fairness index and visual max-min fairness. AECN has fewer packet drops and alleviates the lockout phenomenon and yields higher goodput than ECN.

The Internet Engineering Task Force (IETF) has recently released network mobility standards that allow deployment of TCP/IP networks onboard a vehicle and maintain permanent network connectivity to the Internet via a vehicular mobile router. This recent development opens up new opportunities for providing efficient mobile computing for users on the move, especially for commuters traveling on public transports. Moreover, central and coordinated management of mobility in a single router, rather than by each user device individually, has numerous advantages. In this architecture, however, it becomes challenging to guarantee network performance due to the mobility of the network and inherently vulnerable nature of wireless links. In this thesis, a detailed performance study of onboard networks is conducted. It has been shown that disruptions in the mobile router connectivity can significantly degrade network throughput. Moreover, factors such as the limited wireless bandwidth of the access link, variations in the bandwidth due to technology switching, and the communication diversity of onboard users all contribute to the problem of unfair sharing of wireless bandwidth. By leveraging the fact that all onboard communications go through the mobile router, performance enhancing solutions are proposed that can be deployed in the mobile router to transparently address the throughput and fairness problems. In this architecture, when the route is known in advance and repetitive (e.g. for public transport or a regularly commuting private vehicle), a certain degree of prediction of impending link disruptions is possible. An anticipatory state freezing mechanism is proposed that relies on the prediction of link disruptions to freeze and unfreeze the state machine of TCP, the widely used transport protocol in the Internet. Simulation study shows that TCP throughput has a non-linear relationship with the prediction accuracy. As prediction accuracy increases, throughput problem diminishes quickly. An adaptive mobile router based fairness control mechanism is proposed to address the unfair sharing of wireless bandwidth in highly dynamic scenarios. The fairness is controlled by dynamically estimating the round-trip-times of all onboard TCP connections and transparently adjusting the protocol control parameters at the router. The thesis also discusses implementation issues for the proposed solutions.

A substantial increase in the number of internet users and the traffic volume bring new challenges for network router design. The current routers need to support higher link data rates and large number of line cards to accommodate the growth of the internet traffic, which necessitate an increase in physical space, power and memory use. Packet forwarding, which is one of the major tasks of a router, has been a performance bottleneck in internet infrastructure. In general, most of the packet forwarding algorithms are implemented in software. However, hardware based solutions has also been popular in recent years because of their high throughput performance. Besides throughput, memory efficiency, incremental/dynamic updates and power consumption are the basic performance challenges for packet forwarding architectures. Hardware-based packet forwarding engines for network routers can be categorized into two groups that are ternary content addressable memory (TCAM) based and dynamic/static random access memory (DRAM/SRAM) based solutions. TCAM-based architectures are simple and hence popular solutions for today&rsquo / s routers. However, they are expensive, power-hungry, and oer little adaptability to new addressing and routing protocols. On the other hand, SRAM has higher density, lower power consumption, and higher speed. The common data structure used in SRAM-based solutions for performing longest prefix matching (LPM) is some type of a tree. In these solutions, multiple memory accesses are required to find the longest matched prefix. Therefore, parallel and pipelining techniques are used to improve the throughput. This thesis studies TCAM and SRAM based parallel and pipelined architectures for high performance packet forwarding. We proposed to use a memory efficient disjoint prefix set algorithm on TCAM based parallel IP packet forwarding engine to improve its performance. As a fundamental contribution of this thesis, we designed an SRAM based parallel, intersecting and variable length multi-pipeline array structure (SAFIL) for trie-based internet protocol (IP) lookup. We also proposed a novel dual port SRAM based high throughput IP lookup engine (SAFILD) which is built upon SAFIL. As an alternative to traditional binary trie, we proposed a memory efficient data structure called compact clustered trie (CCT) for IP lookup. Furthermore, we developed a novel combined length-infix pipelined search (CLIPS) architecture for high performance IPv4/v6 lookup on FPGA. Finally, we designed a memory efficient clustered hierarchical search structure (CHSS) for packet classification. A linear pipelined SRAM-based architecture for CHSS which is implemented on FPGA is also proposed.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: PI; PISA; PIMC; cwnd; TCP. Includes bibliographical references (p. 49-50).

An ad-hoc network is a collection of mobile nodes (wireless communication devices) that transmit data over systems that do not require any centralized control, such as that found in cellular networks. This makes ad-hoc networks suitable for military type applications, since there is no need for an established backbone infrastructure and hence no single-point-of-failure. However, other uses of ad-hoc systems include search and rescue missions, law enforcement operations, commercial and educational communication of laptop (and other handheld device) data, as well as in the transmission of environmental sensor information. The mobile ad-hoc concept brings many design challenges. The dynamic freedom of movement from mobile nodes causes random, sometimes rapidly time changing topologies, which are inappropriate for use through traditional wired protocols. In addition, wireless networks generally contain greater bandwidth, processing and power constraints than their wired counterparts, since they are implemented on embedded mobile, handheld devices. Thus, a different approach is needed in the wireless network domain. This has resulted in wireless routing protocols employing adaptive, multi-hop, distributed methodologies in which each node additionally acts as a router for each of its neighbouring nodes, in order to achieve a large degree of network connectivity. However, due to the broadcast nature of wireless transmissions, ad-hoc systems contain a point-to- multipoint communication architecture, making it well suited to multi-path traffic. One such application is in multicasting, which sends data from one source to two (or more) destinations. But, due to the shared characteristics of the communication channel, such traffic may cause multiple contentions and collisions to occur, which will degrade the efficiency and performance of a protocol. This dissertation examines these different design tradeoffs through the use of a freely available simulation package, known as NS-2 (Network Simulator - version 2). In addition, a novel routing protocol, known as LAMP (Location Aided Multicasting Protocol), is developed to handle time-bounded audio information, which is employed in a network that consists of sixteen commercial handheld devices. LAMP utilizes a destination-sequenced, next-hop routing table to forward multicast data. Since mobility causes neighbouring nodes to continually change, next-hop links need to be periodically updated. But, between each update period, a next-hop link may become broken. Thus, if a packet is required to be routed, for which its' next-hop link is unknown, LAMP reverts to a localized location aided flood to find a path to that destination. However, since flooding causes network congestion, it is only employed when its' table forwarding scheme fails. Results have shown that LAMP improves packet delivery ratios by up to 5% over exisiting flood-limiting schemes: Furthermore, LAMP has been shown to be comparable to leading schemes, even when employed to route data to a single source-destination pair. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references (p.44-45).

Thesis (M.C.S.)--Carleton University, 2005. / Includes bibliographical references (p. 89-91). Also available in electronic format on the Internet.

Thesis (Ph.D.) - Carleton University, 2006. / Includes bibliographical references (p. 248-260). Also available in electronic format on the Internet.