• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 917
  • 171
  • 61
  • 32
  • 32
  • 26
  • 22
  • 16
  • 16
  • 12
  • 8
  • 8
  • 7
  • 6
  • 5
  • Tagged with
  • 1716
  • 570
  • 459
  • 415
  • 343
  • 266
  • 263
  • 218
  • 195
  • 195
  • 170
  • 155
  • 150
  • 146
  • 139
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Universal Telecommunications Service of Thailand

Tengtrakul, Pitikorn 28 January 2005 (has links)
Thailand is now engaged in the important process of reforming the countrys telecommunications structure. New telecommunications acts have been passed and regulators have been designated to regulate this telecommunications transformation. However, there are many critical details that must be determined. This thesis aims to identify appropriate universal service mechanisms for Thailand. It focuses on universal service with regard to telecommunication regulatory policies for fixed telephone services. This study uses a qualitative analysis of multiple case comparisons as the methodology for exploring the universal service mechanisms in five countries: the United States of America, the United Kingdom, Chile, Peru and Malaysia. Each of these countries was selected after consideration of the telecommunications mechanisms they have implemented, as well as for key criteria that typically should be considered when choosing universal service mechanisms. After considering the key criteria with regard to characteristics of telecommunications in Thailand, this thesis concludes that the appropriate universal service mechanism for the country is a hybrid scheme that employs both Mandatory Service Obligations (MSOs) and Auctions through the Universal Service Fund (USF). The application of MSOs has been chosen to ensure that telecommunications providers fulfill their universal service obligations, while auction has been chosen in compliance with the USF. The recommendations from this thesis can serve as guidelines for universal service for telecommunications regulatory policies of Thailand. Nevertheless, additional specific details of implementation should be considered and other comprehensive methodologies should be conducted in order to increase the ability to generalize these results.
2

Designing a National Emergency Wireless System

Anderson, Rick 28 July 2005 (has links)
Designing a National Emergency Wireless System Richard Anderson, B.S. University of Pittsburgh, 2005 This paper looks at combining modern telephone services together for emergency support services. The newer services provided by 2.5 and 3G technologies, such as broadcast text messaging, GPS tracking and the ability to send video and images, has expanded our capabilities for sending information to a large consumer base. By taking these services, and targeting them towards emergency response crews as well as civilians, a new emergency system can be designed. Utilizing leading edge wireless technologies will allow workers to communicate faster, distribute information effectively, and provide better support during an emergency. Civilians can be warned of an impending disaster and can be alerted as how to proceed in an emergency situation. These new services can be added to the current infrastructure and can work on many of the devices already in use on the current cellular network.
3

OPTIMIZING ROUTING AND WAVELENGTH ALLOCATION IN OPTICAL CORE NETWORKS

Shringi, Jagrati 31 January 2006 (has links)
Optical networks using wavelength division multiplexing (WDM) technology have emerged as an attractive solution for meeting rapidly growing demands for Bandwidth. WDM allows the same fiber to carry many signals independently as long as each uses a different wavelength. Connections must therefore be routed and assigned to wavelengths such that no two calls use the same wavelength on the same link. This is known as the routing and wavelength assignment (RWA) problem. If full conversion is available at all nodes, the WDM network is equivalent to a circuit-switched network; however, the high cost of wavelength converters often makes it desirable to keep the amount of conversion used in the network to a minimum. Since the performance of this architecture is tightly linked to the efficient establishment of light paths, a detailed investigation of the lightpath establishment problem is conducted. This study addresses an important problem in wavelength routed all-optical WDM networks: how to efficiently utilize a limited number of resources on statically routed optical core. We first formulate a routing scheme to balance channels across the network and then introduce a wavelength allocation scheme to reduce number of wavelength channel and wavelength conversion. Both theoretical and simulation results are presented. By using the proposed routing scheme and wavelength assignment algorithm, only a very small number of wavelength converters are needed to achieve same performance as that of the full-Complete Wavelength conversion. This objective is achieved in the study by evolving the routing and wavelength assignment scheme using very simple and intuitive steps.
4

Energy Consumption of Encryption Schemes in Wireless Devices

Hirani, Sohail A 12 June 2003 (has links)
Resources in the wireless environment are limited. The processor has limited capacity and there is limited battery power available. The increasing demand for services on wireless devices has pushed technical research into finding ways to overcome these limitations. As the penetration of wireless devices increases and applications become more critical every day, security of wireless networks has come under heavy scrutiny. However since most of the current communication algorithms are designed and tested for use in the wired environment, they cannot be used directly in Wireless LANs. Encryption, which is the backbone of security protocols, is computationally intensive and consumes energy and computational resources that are limited in wireless devices. The current encryption standards used in wireless systems are not very secure. Also, the wireless network interface draws a significant fraction of total power consumed by the mobile device. Collisions and retransmissions lead to additional consumption of power. To design energy efficient secure protocols for wireless devices there is a need to understand how encryption affects the consumption of battery power with and without data transmission. The research work carried out in this thesis, provides results that encourage having encryption schemes as software implementation in Wireless LANs and provides results reflecting the advantages of doing so. Various symmetric key and asymmetric key algorithms have been evaluated with different key sizes and on different devices. Effect of varying signal to noise ratio and varying packet sizes has been studied. Further, some suggestions for design of secure communications systems to handle the varying wireless environment have been provided.
5

The Effect of Voice Packet Size on End-To-End delay in 802.11b Networks

Phalgun, Haritha 12 June 2003 (has links)
Voice over IP (VoIP) uses the existing data networks to support voice services. It has a broad appeal in that it is currently unregulated and calls can be placed free of cost to any part of the globe. The integration of voice traffic with data traffic opens up opportunities for new revenue stream for Internet Service Providers. However, in mixing data types the constraints on each data type must still be met and unlike regular data, voice networks are chiefly limited by end-to-end delay. In the case of packet switched networks delay becomes a determining factor in the quality of the voice call and therefore the success of VoIP. At the same time, WLANs are becoming widely adopted due to the simplicity in installation and convenience offered. Advancement in technology now enables WLANs to provide most of the facilities provided by their wired counterparts with the added benefit of mobility at a very low cost. The benefits of combining IP telephony and WLANs can be effectively utilized if the control over end-to-end delay can be achieved. In conventional IP telephony the voice packets travel across the wired Internet. We developed a study in which the final hop on each end of the communication channel is a wireless 802.11b network. Results show that with a wireless network at the transmitting end the delay characteristics change considerably.
6

A CLUSTERING-BASED SELECTIVE PROBING FRAMEWORK TO SUPPORT INTERNET QUALITY OF SERVICE ROUTING

Jariyakul, Nattaphol 06 January 2005 (has links)
The advent of the multimedia applications has triggered widespread interest in QoS supports. Two Internet-based QoS frameworks have been proposed: Integrated Services (IntServ) and Differentiated Services (DiffServ). IntServ supports service guarantees on a per-flow basis. The framework, however, is not scalable due to the fact that routers have to maintain a large amount of state information for each supported flow. DiffServ was proposed as an alternate solution to address the lack of scalability of the IntServ framework. DiffServ uses class-based service differentiation to achieve aggregate support for QoS requirements. This approach eliminates the need to maintain per-flow states on a hop-by-hop basis and reduces considerably the overhead routers incur in forwarding traffic. Both IntServ and DiffServ frameworks focus on packet scheduling. As such, they decouple routing from QoS provisioning. This typically results in inefficient routes, thereby limiting the ability of the network to support QoS requirements and to manage resources efficiently. The goal of this thesis is to address this shortcoming. We propose a scalable QoS routing framework to identify and select paths that are very likely to meet the QoS requirements of the underlying applications. The tenet of our approach is based on seamlessly integrating routing into the DiffServ framework to extend its ability to support QoS requirements. Scalability is achieved using selective probing and clustering to reduce signaling and routers overhead. The major contributions of this thesis are as follows: First, we propose a scalable routing architecture that supports QoS requirements. The architecture seamlessly integrates the QoS traffic requirements of the underlying applications into a DiffServ framework. Second, we propose a new delay-based clustering method, referred to as d-median. The proposed clustering method groups Internet nodes into clusters, whereby nodes in the same cluster exhibit equivalent delay characteristics. Each cluster is represented by anchor node. Anchors use selective probing to estimate QoS parameters and select appropriate paths for traffic forwarding. A thorough study to evaluate the performance of the proposed d-median clustering algorithm is conducted. The results of the study show that, for power-law graphs such as the Internet, the d-median clustering based approach outperforms the set covering method commonly proposed in the literature. The study shows that the widely used clustering methods, such as set covering or k-median, are inadequate to capture the balance between cluster sizes and the number of clusters. The results of the study also show that the proposed clustering method, applied to power-law graphs, is robust to changes in size and delay distribution of the network. Finally, the results suggest that the delay bound input parameter of the d-median scheme should be no less than 1 and no more than 4 times of the average delay per one hop of the network. This is mostly due to the weak hierarchy of the Internet resulting from its power-law structure and the prevalence of the small-world property.
7

Energy Consumption in Wireless Sensor Networks Using GSP

Calle Torres, Maria Gabriela 27 July 2006 (has links)
The energy consumption rate for sensors in a wireless sensor network varies greatly based on the protocols the sensors use for communications. The Gossip-Based Sleep Protocol (GSP) implements routing and some MAC functions in an energy conserving manner. The effectiveness of GSP has already been demonstrated via simulation. However, no prototype system has been previously developed. GSP was implemented on the Mica2 platform and measurements were conducted to determine the improvement in network lifetime. Results for energy consumption, transmitted and received power, minimum voltage supply required for operation, effect of transmission power on energy consumption, and different methods for measuring lifetime of a sensor node are presented. The behaviour of sensor nodes when they are close to their end of lifetime is described and analyzed. A comparison with other models for energy consumption is made and suggestions for future work are presented.
8

ADAPTIVE SPEECH QUALITY IN VOICE-OVER-IP COMMUNICATIONS

Myakotnykh, Evgeny 14 May 2008 (has links)
The quality of VoIP communication relies significantly on the network that transports the voice packets because this network does not usually guarantee the available bandwidth, delay, and loss that are critical for real-time voice traffic. The solution proposed here is to manage the voice-over-IP stream dynamically, changing parameters as needed to assure quality. The main objective of this dissertation is to develop an adaptive speech encoding system that can be applied to conventional (telephony-grade) and wideband voice communications. This comprehensive study includes the investigation and development of three key components of the system. First, to manage VoIP quality dynamically, a tool is needed to measure real-time changes in quality. The E-model, which exists for narrowband communication, is extended to a single computational technique that measures speech quality for narrowband and wideband VoIP codecs. This part of the dissertation also develops important theoretical work in the area of wideband telephony. The second system component is a variable speech-encoding algorithm. Although VoIP performance is affected by multiple codecs and network-based factors, only three factors can be managed dynamically: voice payload size, speech compression and jitter buffer management. Using an existing adaptive jitter-buffer algorithm, voice packet-size and compression variation are studied as they affect speech quality under different network conditions. This study explains the relationships among multiple parameters as they affect speech transmission and its resulting quality. Then, based on these two components, the third system component is a novel adaptive-rate control algorithm that establishes the interaction between a VoIP sender and receiver, and manages voice quality in real-time. Simulations demonstrate that the system provides better average voice quality than traditional VoIP.
9

Exploring Jamming Attacks Using OPNET 12.0

Gonzalez, Jesus 31 January 2008 (has links)
Ad-hoc Networks are one of the most important achievements of current technology; they can provide communication without needing a fixed infrastructure, which makes them suitable for communication in disaster areas or when quick deployment is needed. However, since this kind of network uses the wireless medium for communication, it is susceptible to malicious exploitation at different layers. One of these attacks is a kind of denial of service attack (DoS) that interferes with the radio transmission channel, this is also known as a jamming attack. In this kind of attack, an attacker emits a radio signal that disturbs the energy of the packets causing many errors in the packet currently being transmitted. Another version of this attack is to constantly emit random semi-valid packets to keep the medium busy all the time, preventing the honest nodes from switching from the listening mode to the transmitting mode. In rough environments where there is constant traffic, a jamming attack causes serious problems; therefore measures to prevent this attack are required. The purpose of this thesis is to explore the underlying principles of jamming attacks (i.e., the effects of modulation techniques, interarrival times of packets, transmitters and jammers power) using Opnet® as the simulation tool. This work will be helpful so that in future research a useful, practical and effective solution can be created to countermeasure the effects of jamming attacks. The objective here is to understand, modify, and employ the models in OPNET 12.0® to simulate jamming attacks and understand the limitations of the available models.
10

Inter-Domain Authentication for Seamless Roaming in Heterogeneous Wireless Networks

Tuladhar, Summit Raj 31 January 2008 (has links)
The convergence of diverse but complementary wireless access technologies and inter-operation among administrative domains have been envisioned as crucial for the next generation wireless networks that will provide support for end-user devices to seamlessly roam across domain boundaries. The integration of existing and emerging heterogeneous wireless networks to provide such seamless roaming requires the design of a handover scheme that provides uninterrupted service continuity while facilitating the establishment of authenticity of the entities involved. The existing protocols for supporting re-authentication of a mobile node during a handover across administrative domains typically involve several round trips to the home domain, and hence introduce long latencies. Furthermore, the existing methods for negotiating roaming agreements to establish inter-domain trust rely on a lengthy manual process, thus, impeding seamless roaming across multiple domains in a truly heterogeneous wireless network. In this thesis, we present a new proof-token based authentication protocol that supports quick re-authentication of a mobile node as it moves to a new foreign domain without involving communication with the home domain. The proposed proof-token based protocol can also support establishment of spontaneous roaming agreements between a pair of domains that do not already have a direct roaming agreement, thus allowing flexible business models to be supported. We describe details of the new authentication architecture, the proposed protocol, which is based on EAP-TLS and compare the proposed protocol with existing protocols.

Page generated in 0.2066 seconds