10,164 research outputs found
Cross-layer design of multi-hop wireless networks
MULTI -hop wireless networks are usually defined as a collection of nodes
equipped with radio transmitters, which not only have the capability to
communicate each other in a multi-hop fashion, but also to route each othersâ data
packets. The distributed nature of such networks makes them suitable for a variety of
applications where there are no assumed reliable central entities, or controllers, and
may significantly improve the scalability issues of conventional single-hop wireless
networks.
This Ph.D. dissertation mainly investigates two aspects of the research issues
related to the efficient multi-hop wireless networks design, namely: (a) network
protocols and (b) network management, both in cross-layer design paradigms to
ensure the notion of service quality, such as quality of service (QoS) in wireless mesh
networks (WMNs) for backhaul applications and quality of information (QoI) in
wireless sensor networks (WSNs) for sensing tasks. Throughout the presentation of
this Ph.D. dissertation, different network settings are used as illustrative examples,
however the proposed algorithms, methodologies, protocols, and models are not
restricted in the considered networks, but rather have wide applicability.
First, this dissertation proposes a cross-layer design framework integrating
a distributed proportional-fair scheduler and a QoS routing algorithm, while using
WMNs as an illustrative example. The proposed approach has significant performance
gain compared with other network protocols. Second, this dissertation proposes
a generic admission control methodology for any packet network, wired and
wireless, by modeling the network as a black box, and using a generic mathematical
0. Abstract 3
function and Taylor expansion to capture the admission impact. Third, this dissertation
further enhances the previous designs by proposing a negotiation process,
to bridge the applicationsâ service quality demands and the resource management,
while using WSNs as an illustrative example. This approach allows the negotiation
among different service classes and WSN resource allocations to reach the optimal
operational status. Finally, the guarantees of the service quality are extended to
the environment of multiple, disconnected, mobile subnetworks, where the question
of how to maintain communications using dynamically controlled, unmanned data
ferries is investigated
Creating an Agent Based Framework to Maximize Information Utility
With increased reliance on communications to conduct military operations, information centric network management becomes vital. A Defense department study of information management for net-centric operations lists the need for tools for information triage (based on relevance, priority, and quality) to counter information overload, semi-automated mechanisms for assessment of quality and relevance of information, and advances to enhance cognition and information understanding in the context of missions [30]. Maximizing information utility to match mission objectives is a complex problem that requires a comprehensive solution in information classification, in scheduling, in resource allocation, and in QoS support. Of these research areas, the resource allocation mechanism provides a framework to build the entire solution. Through an agent based mindset, the lessons of robot control architecture are applied to the network domain. The task of managing information flows is achieved with a hybrid reactive architecture. By demonstration, the reactive agent responds to the observed state of the network through the Unified Behavior Framework (UBF). As information flows relay through the network, agents in the network nodes limit resource contention to improve average utility and create a network with smarter bandwidth utilization. While this is an important result for information maximization, the agent based framework may have broader applications for managing communication networks
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Flexible cross layer design for improved quality of service in MANETs
This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel UniversityMobile Ad hoc Networks (MANETs) are becoming increasingly important because of their unique characteristics of connectivity. Several delay sensitive applications are starting to appear in these kinds of networks. Therefore, an issue in concern is to guarantee Quality of Service (QoS) in such constantly changing communication environment. The classical QoS aware solutions that have been used till now in the wired and infrastructure wireless networks are unable to achieve the necessary performance in the MANETs. The specialized protocols designed for multihop ad hoc networks offer basic connectivity with limited delay awareness and the mobility factor in the MANETs makes them even more unsuitable for use. Several protocols and solutions have been emerging in almost every layer in the protocol stack.
The majority of the research efforts agree on the fact that in such dynamic environment in order to optimize the performance of the protocols, there is the need for additional information about the status of the network to be available. Hence, many cross layer design approaches appeared in the scene. Cross layer design has major advantages and the necessity to utilize such a design is definite. However, cross layer design conceals risks like architecture instability and design inflexibility. The aggressive use of cross layer design results in excessive increase of the cost of deployment and complicates both maintenance and upgrade of the network. The use of autonomous protocols like bio-inspired mechanisms and algorithms that are resilient on cross layer information unavailability, are able to reduce the dependence on cross layer design. In addition, properties like the prediction of the dynamic conditions and the adaptation to them are quite important characteristics.
The design of a routing decision algorithm based on Bayesian Inference for the prediction of the path quality is proposed here. The accurate prediction capabilities and the efficient use of the plethora of cross layer information are presented.
Furthermore, an adaptive mechanism based on the Genetic Algorithm (GA) is used to control the flow of the data in the transport layer. The aforementioned flow control mechanism inherits GAâs optimization capabilities without the need of knowing any details about the network conditions, thus, reducing the cross layer information dependence. Finally, is illustrated how Bayesian Inference can be used to suggest configuration parameter values to the other protocols in different layers in order to improve their performance.National Foundation of Scholarships of Greece(I.K.Y.
Inclusive education in India: interpretation, implementation, and issues
Children with disabilities are a minority that are not prioritised in the context of education programmes in India, although they are often found in many marginalised groups that are catered for if non-disabled ? for example, girls, scheduled tribe, scheduled caste, and other backward caste children. Inclusive education may be a way of merging these childrenâs needs in order to improve school quality and achieve EFA. However, a dominant special needs conceptualisation of IE in India, combined with negative attitudes towards disability, are currently preventing this approach. After exploring the relevance of disability and inclusive education in the context of EFA, this paper analyses the interpretation and implementation of inclusive education in India. The issues and constraints faced by the stakeholders involved, and the implications these may have, particularly for children with disabilities, lead to the conclusion that a twin-track approach to disability may assist not only in improving education access, but also the reconceptualisation of inclusive education as a school quality issue. In the long-term, it is hoped that this could assist in fulfilling the right to education for all children
QoS-aware Mobility Management in IP-based Communication Networks
Der allgegenwĂ€rtige Zugang zu Informationen, jederzeit und ĂŒberall, ist ein
wichtiges Merkmal kĂŒnftiger All-IP-Mobilfunktnetze, die verschiedene
Systeme miteinander verbinden, dabei dynamischer und flexibler sein
werden. Der Einsatz dieser Netze erfordert es jedoch, viele
Herausforderungen zu ĂŒberwinden. Eine der wichtigsten im Rahmen dieser
Arbeit, ist die Frage, wie Quality of Service (QoS) Eigenschaften in
solchen hoch dynamischen, mobilen Umgebungen zu garantieren sind. BekanntermaĂen beeinflusst die MobilitĂ€t von Mobilknoten (MN) die DienstgĂŒte in mobilen Netzen, da QoS-Parameters fĂŒr
die Ende-zu-Ende-Kommunikation vereinbart werden. Daher mĂŒssen Lösungen
entwickelt werden, die nahtlose MobilitÀt, bei gleichzeitigen QoS-Garantien
nach Handoffs, unterstĂŒtzen. Diese Herausforderung ist das Hauptziel der
vorliegenden Dissertation, die einen umfassenden Ăberblick ĂŒber die
bestehenden MobilitÀts- und QoS-Managment-Lösungen in IP-basierten Netzen
liefert, gefolgt von einem Einblick in Methoden zur Kopplung von
MobilitÀtsmanagement und QoS-Lösungen. Nach Betrachtung der Vor- und
Nachteile bestehender AnsÀtze, kommt die Dissertation zu dem Schluss, dass
hybride Strategien vielversprechend sind und zu praktikablen Lösungen
weiterentwickelt werden können, die sowohl MobilitÀts- als auch
QoS-Anforderungen auf effiziente Weise,in allen zukĂŒnftigen IP-Mobilfunknetzen erfĂŒllen können. Auf dieser Grundlage schlĂ€gt die Dissertation ein neues Hybrid-Protokoll, genannt
"QoS-aware Mobile IP Fast Authentication Protocol" (QoMIFA), vor. Unser
Vorschlag integriert MIFA als MobilitÀts-Management-Protokoll mit RSVP als
QoS Reservierungsprotokoll. MI-FA wird aufgrund seiner FĂ€higkeit zu
schnellen, sicheren und robusten Handoffs gewÀhlt. RSVP hingegen dient als
Standardlösung zur Bereitstellung von QoS in bestehenden IP-basierten
Netzen. Unter Einhaltung der Hybrid-Architektur wird RSVP um ein neues
Objekt, genannt "Mobility Object" erweitert, welches
MIFA-Kontrollnachrichten kapselt. Nach der Spezifikation des neuen
Vorschlags, bewertet die Dissertation auch seine Leistung im Vergleich zu
dem bekannten "Simple QoS Signaling Protocol" (Simple QoS), mittels
Simulationsstudien, modelliert mit dem "Network Simluator 2" (NS2). In der
Auswertung werden der Einflusses der Netzwerklast und der Geschwindigkeit
des Mobilknotens untersucht. Die hierzu verwendeten Leistungsparameter
umfassen die Ressourcen-Reservierungs-Latenz, die Anzahl verlorener Pakete
pro Handoff, die Anzahl der, vor Abschluss der Reservierung, mit
Best-Effort-Eigenschaften ĂŒbertragenen Pakete pro Handoff und die
Wahrscheinlichkeit von VerbindungsabbrĂŒchen. Unsere mittels Simulation
erzielten Ergebnisse zeigen, dass QoMIFA schnelle und nahtlose Handoffs mit
schneller Ressourcenreservierung nach Handoffs kombinieren kann. Unter
BerĂŒcksichtigung des Einflusses der Netzwerklast, ist nachweisbar, dass
QoMIFA eine besser Leistung als Simple QoS in allen untersuchten Szenarien
mit geringer, mittlerer und hoher Last erreicht. Bei Betrachtung des
Einflusses der Bewegungsgeschwindigkeit des Mobilknotens auf die Leistung,
lassen sich unter beiden Protokollen Ping-Pong-Effekte beobachten, welche
zu höheren Ressourcen-Reservierungs-Latenzen, mehr verlorenen Paketen und
mehr Best-Effort-Paketen pro Handoff bei geringeren Geschwindigkeiten
fĂŒhren. Der stĂ€rkste Einfluss dieser Pinp-Pong-Effekte ist jeweils bei 3
km/h zu beobachten. Allerdings verhÀlt sich QoMIFA unter allen untersuchten
Bewegungsgeschwindigkeiten besser als Simple QoS und kann Mobilknoten auch
bei hohen Geschwindigkeiten bedienen. In Anschluss an die
simulationsgestĂŒtzte Evaluierung, schĂ€tzt die Dissertation die
Signalisierungskosten beider Protokolle unter Betrachtung der Kosten fĂŒr
Ortslokalise-rung und Paketzustellung. Im Ergebnis erreicht QoMIFA die
zuvor genannten Leistungsverbesserungen auf Kosten von gröĂeren
Ortslokalisierungskosten und leicht höherer Paketzustellungskosten.Ubiquitous access to information anywhere, anytime and anyhow is an
important feature of future all-IP mobile communication networks, which
will interconnect various systems and be more dynamic and flexible. The
deployment of these networks, however, requires overcoming many challenges.
One of the main challenges of interest for this work is how to provide
Qual-ity of Service (QoS) guarantees in such highly dynamic mobile
environments.As known, mobility of Mobile Nodes (MNs) affects the QoS in
mobile networks since QoS parameters are made for end-to-end
communications. Therefore, it is a challenge to develop new solutions
capable of supporting seamless mobility while simultaneously providing QoS
guarantees after handoffs. Addressing this challenge is the main objective
of this dissertation, which provides a comprehensive overview of mobility
management solutions and QoS mech-anisms in IP-based networks followed by
an insight into how mobility management and QoS solutions can be coupled
with each other. Following the highlight of the state of art along with the
pros and cons of existing approaches, the dissertation concludes that
hybrid strategies are promising and can be further developed to achieve
solutions that are capable of simultaneous-ly supporting mobility and QoS,
simple from the implementation point of view, efficient and applicable to
future all-IP mobile communication networks.Based on this, the dissertation
proposes a new hybrid proposal named QoS-aware Mobile IP Fast
Authentication Protocol (QoMIFA). Our proposal integrates MIFA as a
mobility man-agement protocol with RSVP as a QoS reservation protocol. MIFA
is selected due to its capa-bility of the provision of fast, secure and
robust handoffs, while RSVP is chosen because it presents the standard
solution used to support QoS in existing IP-based networks. The hybrid
architecture is retained by introducing a new object, called âmobility
objectâ, to RSVP in or-der to encapsulate MIFA control messages.Following
the specification of the new proposal, the dissertation also evaluates its
perfor-mance compared to the well-known Simple QoS signaling protocol
(Simple QoS) by means of simulation studies modeled using the Network
Simulator 2 (NS2). The evaluation compris-es the investigation of the
impact of network load and MN speed. The performance measures we are
interested in studying comprise the resource reservation latency, number of
dropped packets per handoff, number of packets sent as best-effort per
handoff until the reservation is accomplished and probability of dropping
sessions. Our simulation results show that QoMIFA is capable of achieving
fast and smooth handoffs in addition to its capability of quickly
re-serving resources after handoffs. Considering the impact of network
load, QoMIFA outper-forms Simple QoS in all studied scenarios (low- ,
middle- and high-loaded scenarios). With respect to the impact of MN speed,
it can be observed that the impact of ping-pong effects is seen with both
protocols and results in higher resource reservation latency, more dropped
packets per handoff and more best-effort packets per handoff at low speeds
than at higher ones. The worst impact of ping-pong effects is seen at a
speed of 3 km/h when employing QoMIFA and Simple QoS, respectively.
However, QoMIFA remains performing significantly better than Simple QoS
under all studied MN speeds and can even properly serve MNs mov-ing at high
speeds.Following the simulative evaluation, the dissertation estimates the
signaling cost of both stud-ied protocols with respect to the location
update and packet delivery cost. Our results show that QoMIFA achieves the
above mentioned performance improvements at the cost of greater location
update cost and slightly higher packet delivery cost than Simple QoS
Advance Reservations of Bandwidth in Computer Networks
In dieser Arbeit wurden die unterschiedlichen Aspekte untersucht, die die LeistungsfĂ€higkeit eines Systems zur Vorausreservierung in Computer-Netzwerken bestimmen. Basierend auf einer Architektur, welche den Basisdienst fĂŒr Vorausreservierungen mittels Multiprotocol Label Switching (MPLS) zur VerfĂŒgung stellt, wurden innerhalb eines Netzwerkmanagementsystems unterschiedliche Dienste implementiert und simulativ auf ihre Auswirkungen auf die LeistungsfĂ€higkeit des Netzwerks in Bezug auf Anzahl zugelassener Datenströme sowie transportierte Datenmenge untersucht. Diese Dienste erweitern in entscheidendem MaĂe auch die Breite des Dienstangebots in Netzwerken im Vergleich zu bisherigen Implementierungen. So ist es möglich bei Angabe einer festen Datenmenge vom Netzwerkmanagement geeignete Ăbertragungszeiten und raten bestimmen zu lassen. Diese Parameter werden dann, zum Beispiel in Form von Service Level Agreements (SLA), vom Netzwerkmanagement garantiert und sind insbesondere in Umgebungen wichtig, in denen die Ăbertragung sehr groĂer Datenmengen notwendig ist, beispielsweise in Grid-Computing- Systemen. Die erweiterten Dienste dienen jedoch nicht nur den Nutzern, sondern sind auch fĂŒr Betreiber interessant, da sie es ermöglichen die LeistungsfĂ€higkeit des Netzwerkes zu erhöhen. Dies ist insbesondere zusammen mit weiteren Verfahren möglich, die die zusĂ€tzlich zur VerfĂŒgung stehenden Informationen ĂŒber zeitliche Aspekte, wie die Dauer von Ăbertragungen, nutzen. Im Vergleich zu den heute hauptsĂ€chlich betrachteten Systemen zur sog. unmittelbaren Reservierung, kann bei geschicktem Einsatz der hier implementierten Dienste und Verfahren eine deutliche Verbesserung der Leistung erzielt werden. Hinzu kommen bei Vorausreservierungen die erheblichen Vorteile fĂŒr die Nutzer eines Netzwerkes, wie z.B. der oben beschriebene Datentransfer. Die Leistung eines Netzwerkes bemisst sich jedoch nicht nur an der transportierten Datenmenge, sondern auch am Verhalten im Fehlerfall und der Geschwindigkeit des Managementsystems. Dazu wurden im Rahmen dieser Arbeit mögliche Strategien zur Reaktion von Vorausreservierungssystemen im Fall von Link-AusfĂ€llen entwickelt und untersucht. Auch hier kommt dem zeitlichen Aspekt eine wichtige Bedeutung zu. Es erwies sich als erfolgreich, nicht nur unmittelbar betroffene Datenströme sondern auch solche, die zwar bereits bekannt, jedoch noch nicht aktiv waren, in die Fehlerbehandlungsstrategie mit einzubeziehen. Datenstrukturen, die von der Zugangskontrolle des Managementsystems benötigt werden und dort die Geschwindigkeit maĂgeblich bestimmen, wurden unter den Aspekten der Zugriffsgeschwindigkeit und des Speicherverbrauchs untersucht. Hierbei wurde gezeigt, dass Arrays erhebliche Vorteile im Hinblick auf beide Aspekte haben und in den meisten FĂ€llen einer Baumstruktur, die speziell fĂŒr die Aufgabe innerhalb der Zugangskontrolle entwickelt wurde, ĂŒberlegen sind. Die Nutzung von Vorausreservierungen in Computer-Netzwerken ist damit eine nĂŒtzliche und wichtige Erweiterung der FunktionalitĂ€t eines Netzwerkes sowohl in Bezug auf das zur VerfĂŒgung stehende Angebot an Diensten, als auch im Hinblick auf die LeistungsfĂ€higkeit des Netzwerkes.In this thesis, the impact of using advance reservations of bandwidth in a computer network on the performance for both clients and operators of the network is examined. Based on an architecture that uses multi-protocol label switching (MPLS) controlled by bandwidth brokers, a number of services that - compared to todays best-effort or immediate reservation networks - provide an enhanced functionality for clients were developed. These services allow clients to specify requests in a less stringent way than currently necessary, for example, it is possible to define only the amount of data to be transmitted between two network endpoints and the management system then determines suitable transmission parameters such as start and stop time and transmission rate. This functionality provides reliable feedback to clients and can serve as a foundation for providing service-level agreements, e.g., guaranteeing deadlines for the transmission of a certain amount of data. The additional services can also be used by network operators to improve the overall utilization of the network. In addition, the various opportunities of using the additional temporal dimension of the advance reservation service are suitable to improve the network performance. It can be shown that the amount of blocked requests and bandwidth can be considerably decreased making use of both services and the additional information available in the given environment. Besides the achievable throughout and amount of admitted requests, the term performance in the context of advance reservation systems also covers other aspects such as failure recovery strategies and the processing time required by the network management system. In the thesis, several strategies to be applied in case of link failures are outlined and examined with respect to their applicability and achievable performance. For example, it can be shown that it is worthwhile to consider not only flows which are active at the time a failure occurs but also to take inactive but already admitted flows into account in order to achieve the best possible performance. In addition to failure recovery, also the processing speed of the management system is of importance. For that purpose, in particular the data structures used to store the current and future network status need to be examined since they dominate the processing time of the management system. Two data structures, arrays and a tree which was especially designed for this purpose were examined, showing that arrays are superior with respect to processing speed and memory consumption in almost any environment
Comparative Functional Analysis of Air Force and Commercially Available Transportation Information Management Systems
The Air Force currently relies on two transportation information management systems for managing cargo and passenger movements throughout the Defense Transportation System. The two systems are Global Air Transportation Execution System (GATES) and Cargo Movement Operations System (CMOS). Although GATES and CMOS have evolved from legacy systems created during the 1980s, both systems are used to process cargo and passengers while providing the information needed to maintain in-transit visibility (ITV) and manage each movement. The purpose of this research is to identify commercially available logistics software packages and determine whether they provide the same functionality as the two Air Force information systems currently employed. Using a case study methodology, the researcher collected information on logistics software provided by SAP, Oracle, and PeopleSoft. A gap analysis was then conducted to identify the percentage of similarity between the Air Force and commercial systems. The results of the research show SAP having the highest percentage of similarity with each of the Air Force systems followed by Oracle and then PeopleSoft
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