Single and entangled photon manipulation for photonic quantum technologies

Photonic quantum technologies that harness the fundamental laws of quantum physics open the possibility of developing quantum computing and communication that could show unprecedented computational power on specific problems and unconditional information security, respectively. However, the lack of high-efficiency single-photon sources and integrated photonic circuits that can generate, manipulate and analyse entanglement states are the major hurdles to demonstrate the quantum advantages. The potential solutions are clearly explained in this thesis. Chapter 1 provides a brief overview that explains the theme of each chapter. Chapter 2 emphasises the importance of a high-efficiency single-photon source and an integrated time-bin entanglement chip, after explaining the advantages of photonic quantum computing and communication over their classical counterparts. In Chapter 3, three different temporal multiplexing schemes are experimentally demonstrated as the potential solutions to build a high-efficiency single-photon source. Chapter 3 also identifies the potential limitations of temporal multiplexing with high repetition rate. In Chapter 4, the linear processing circuits and nonlinear photon source are separately demonstrated in a low-loss double-stripe silicon nitride waveguide. In the final section of Chapter 4, an integrated silicon nitride time-bin entanglement chip that combines linear processing circuits and nonlinear photon sources is demonstrated as a potential solution to build a robust, scalable and cost-efficient quantum network in the real world. After a succinct summarisation, the final chapter briefly discusses the promising strategies and platforms to build an integrated high-efficiency single-photon source and an integrated quantum node with broad bandwidth and long storage time

Mosh: An Interactive Remote Shell for Mobile Clients

Mosh (mobile shell) is a remote terminal application that supports intermittent connectivity, allows roaming, and speculatively and safely echoes user keystrokes for better interactive response over high-latency paths. Mosh is built on the State Synchronization Protocol (SSP), a new UDP-based protocol that securely synchronizes client and server state, even across changes of the client’s IP address. Mosh uses SSP to synchronize a character-cell terminal emulator, maintaining terminal state at both client and server to predictively echo keystrokes. Our evaluation analyzed keystroke traces from six different users covering a period of 40 hours of real-world usage. Mosh was able to immediately display the effects of 70% of the user keystrokes. Over a commercial EV-DO (3G) network, median keystroke response latency with Mosh was less than 5 ms, compared with 503 ms for SSH. Mosh is free software, available from http://mosh.mit.edu. It was downloaded more than 15,000 times in the first week of its release.National Science Foundation (U.S.) (NSF grant 1040072)National Science Foundation (U.S.) (NSF grant 0721702

On the effectiveness of an optimization method for the traffic of TCP-based multiplayer online games

This paper studies the feasibility of using an optimization method, based on multiplexing and header compression, for the traffic of Massively Multiplayer Online Role Playing Games (MMORPGs) using TCP at the Transport Layer. Different scenarios where a number of flows share a common network path are identified. The adaptation of the multiplexing method is explained, and a formula of the savings is devised. The header compression ratio is obtained using real traces of a popular game and a statistical model of its traffic is used to obtain the bandwidth saving as a function of the number of players and the multiplexing period. The obtained savings can be up to 60 % for IPv4 and 70 % for IPv6. A Mean Opinion Score model from the literature is employed to calculate the limits of the multiplexing period that can be used without harming the user experience. The interactions between multiplexed and non-multiplexed flows, sharing a bottleneck with different kinds of background traffic, are studied through simulations. As a result of the tests, some limits for the multiplexing period are recommended: the unfairness between players can be low if the value of the multiplexing period is kept under 10 or 20 ms. TCP background flows using SACK (Selective Acknowledgment) and Reno yield better results, in terms of fairness, than Tahoe and New Reno. When UDP is used for background traffic, high values of the multiplexing period may stress the unfairness between flows if network congestion is severe

Low-Latency Hard Real-Time Communication over Switched Ethernet

With the upsurge in the demand for high-bandwidth networked real-time applications in cost-sensitive environments, a key issue is to take advantage of developments of commodity components that offer a multiple of the throughput of classical real-time solutions. It was the starting hypothesis of this dissertation that with fine grained traffic shaping as the only means of node cooperation, it should be possible to achieve lower guaranteed delays and higher bandwidth utilization than with traditional approaches, even though Switched Ethernet does not support policing in the switches as other network architectures do. This thesis presents the application of traffic shaping to Switched Ethernet and validates the hypothesis. It shows, both theoretically and practically, how commodity Switched Ethernet technology can be used for low-latency hard real-time communication, and what operating-system support is needed for an efficient implementation

On the Efficiency of Voice over Integrated Services using Guaranteed

Abstract-This paper presents an efficiency study of voice over Integrated Services (IntServ). In particular, the Guaranteed Service class is considered. This service class provides a deterministic upper bound on the end-to-end queuing delay. A method to calculate the optimal packetization delay, and hence, the optimal packet size, is presented. Choosing this packet size involves a trade-off between bandwidth efficiency and delay. Two scenarios are considered in this paper: an IP-phone-to-IP-phone and a gateway-to-gateway scenario. For the latter scenario two multiplexing approaches are evaluated and it is shown that they achieve approximately equal bandwidth efficiency. In addition our results demonstrate that with aggregated voice flows on one reserved bit pipe (gateway-to-gateway scenario) high bandwidth efficiency can be achieved. Index terms--IntServ, Voice over IP, efficiency A. INTRODUCTION 1st. Background Introducing telephony services on IP networks brings its own challenges with respect to voice quality, call set-up time and reliability. The performance of a VoIP network should be comparable to the current PSTN. Especially, the voice quality is of great concern. It depends on many parameters: on the application layer the type of codec, packetization and dejittering delay and on the transport layer the one-way delay, jitter and packet loss. The Quality of Service (QoS) of packet switched networks (e.g. IntServ) controls the transport parameters. The requirements for these parameters are requested by the voice application such that together with the application parameters a certain desired speech quality is obtained. By offering different classes of speech quality, an operator is able to offer telephony services at different prices, targeting different market segments. 2nd. Overview of previous work Telephony has very stringent delay requirements. When perfect echo control is applied, the mouth-to-ear delay should not exceed 150 ms in order to obtain traditional PSTN quality This paper extends these results with several contributions. First, for the calculations of the optimal packetization delay the (static) dejittering delay is also taken into account. Second, the bandwidth efficiency is studied for different types of codecs and third, the gateway-to-gateway scenario is considered. In other words, the scenario where a single reservation is made for an aggregate of voice flows. In this paper we first consider the IP-phone-to-IP-phone scenario with regard to the optimal packet size when a static dejittering delay is used and the bandwidth efficiency when using different types of codecs. Then, we present a study of the gateway-to-gateway scenario. In this case one bit pipe is reserved between two gateways to transport multiple calls. Two methods are considered to multiplex voice flows into a bit pipe. One method is to multiplex IP packets from different flows and the second one is to multiplex voice frames from different voice flows into a single IP packet. 3rd. Contents In Section B the different components of the mouth-to-ear delay are listed. How to specify the traffic parameters that describe a voice flow is shown in Section C. The IntServ architecture is discussed in Section D. The calculation of the optimal packetization delay for an IntServ network with Weighted Fair Queuing (WFQ) schedulers is described in Section E. The efficiency corresponding to this optimal packetization delay is evaluated in Section F. The paper concludes with Section G

Specification of Smart AP solutions - version 2

This document includes the specification of the second version of the Smart Access Point (AP) Solutions, which are being developed within WP3 of the Wi-5 project. After the Literature Review, a global view of the Wi-5 architecture is presented which includes not only the Smart AP Solutions but also the Cooperative Functionalities being developed in WP4. Next, the Smart AP Solutions are described including the summary of the general approach being followed based on Light Virtual APs (LVAPs). The functionalities enabling Radio Resource Management (i.e. Dynamic Channel Allocation, Load Balancing and Power Control) are reported in detail and the current status of the implementation of the solutions is detailed, with a set of improvements aimed at integrating the support of different channels within the Wi-5 framework. A multi-channel handoff scheme has been designed, requiring a good synchronisation between the different events, in order to make the LVAP switching happen at the same moment when the STA switches its channel. In addition, the beacon generation has been modified in order to improve the scalability and to give a better user experience during handoffs. Tests measuring the handoff delay are presented using three wireless cards from different manufacturers, and using as test traffic a flow of an online game with real-time constraints. The results show that fast handovers ranging from 30 to 200 milliseconds can be achieved. The savings provided by frame aggregation, and its effect on subjective quality have also been studied. A methodology including subjective tests with real users has evaluated this effect, using paired comparison. The results indicate that bandwidth usage savings and especially significant packet rate reduction can be obtained without degrading players’ Quality of Experience (QoE), as long as the overall latency is kept under 100ms. An important finding coming from these results is that the players do not register delay variation introduced by multiplexing

Implementación del protocolo GeoNetworking en un software de comunicación V2X

Los Sistemas Inteligentes de Transporte Cooperativos (C-ITS) buscan aumentar la eficiencia del tráfico y mejorar la seguridad vial. Una tecnología clave en los C-ITS es la comunicación V2X. El objetivo de este Trabajo Fin de Máster es la implementación del protocolo GeoNetworking, parte de la arquitectura ETSI C-ITS estandarizada en la Unión Europea, en el software de comunicación V2X OpenC2X desarrollado en el grupo CCS Labs de la Universidad de Paderborn, Alemania. Para ello se ha realizado un estudio detallado de la evolución de los C-ITS y su estandarización en la Unión Europea, para pasar a analizar con mayor profundidad el protocolo GeoNetworking y su integración con el resto de la arquitectura de comunicación. Por último, se ha llevado a cabo el desarrollo del software que integra GeoNetworking en OpenC2X. Aunque GeoNetworking es un protocolo complejo, que maneja una gran cantidad de estructuras de datos auxiliares, se ha conseguido el intercambio de los mensajes CAM y DENM cumpliendo el formato indicado por el estándar, a pesar de no ser una implementación completa del protocolo. Sin embargo, el proceso de implementación nos ha permitido una revisión completa de OpenC2X y se ha llevado a cabo la actualización de varios módulos que utilizaban versiones anteriores de los estándares ETSI.Cooperative Intelligent Transport Systems (C-ITS) aim to increase traffic efficiency and improve road safety. V2X communication is a key technology for C-ITS development. The main purpose of this project is the implementation of the GeoNetworking protocol, part of the ETSI C-ITS architecture standardized in the European Union (EU), in the V2X communication software OpenC2X developed by the CSS Labs group of the University of Paderborn, Germany. For this purpose, a comprehensive study of the evolution of C-ITS and its standardization in the EU has been carried out, to proceed to a more in-depth analysis of the GeoNetworking protocol and its integration within the complete communication architecture. Finally, the development of the software which integrates GeoNetworking in OpenC2X has been carried out. Although GeoNetworking is a complex protocol, which handles a lot of auxiliary data structures, the exchange of CAM and DENM messages has been achieved in compliance with the format indicated in the standard, despite not being a complete implementation of the protocol. However, the implementation process has allowed a complete revision of OpenC2X and the update of several modules that used outdated versions of the ETSI standards had been done.Departamento de Teoría de la Señal y Comunicaciones e Ingeniería TelemáticaMáster en Ingeniería de Telecomunicació

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression

From burstiness characterisation to traffic control strategy : a unified approach to integrated broadbank networks

The major challenge in the design of an integrated network is the integration and support of a wide variety of applications. To provide the requested performance guarantees, a traffic control strategy has to allocate network resources according to the characteristics of input traffic. Specifically, the definition of traffic characterisation is significant in network conception. In this thesis, a traffic stream is characterised based on a virtual queue principle. This approach provides the necessary link between network resources allocation and traffic control. It is difficult to guarantee performance without prior knowledge of the worst behaviour in statistical multiplexing. Accordingly, we investigate the worst case scenarios in a statistical multiplexer. We evaluate the upper bounds on the probabilities of buffer overflow in a multiplexer, and data loss of an input stream. It is found that in networks without traffic control, simply controlling the utilisation of a multiplexer does not improve the ability to guarantee performance. Instead, the availability of buffer capacity and the degree of correlation among the input traffic dominate the effect on the performance of loss. The leaky bucket mechanism has been proposed to prevent ATM networks from performance degradation due to congestion. We study the leaky bucket mechanism as a regulation element that protects an input stream. We evaluate the optimal parameter settings and analyse the worst case performance. To investigate its effectiveness, we analyse the delay performance of a leaky bucket regulated multiplexer. Numerical results show that the leaky bucket mechanism can provide well-behaved traffic with guaranteed delay bound in the presence of misbehaving traffic. Using the leaky bucket mechanism, a general strategy based on burstiness characterisation, called the LB-Dynamic policy, is developed for packet scheduling. This traffic control strategy is closely related to the allocation of both bandwidth and buffer in each switching node. In addition, the LB-Dynamic policy monitors the allocated network resources and guarantees the network performance of each established connection, irrespective of the traffic intensity and arrival patterns of incoming packets. Simulation studies demonstrate that the LB-Dynamic policy is able to provide the requested service quality for heterogeneous traffic in integrated broadband networks