Fast queuing policies via convex relaxation

Traditionally, networking protocol designs have placed much emphasis on point-to-point reliability and efficiency. With the recent rise of mobile and multimedia applications, other considerations such as power consumption and/or Quality of Service (QoS) are becoming increasingly important factors in designing network protocols. As such, we present a new flexible framework for designing robust network protocols under varying network conditions that attempts to integrates various given objectives while satisfying some pre-specified levels of Quality of Service. The proposed framework abstracts a network protocol as a queuing policy, and relies on the optimization methods of convex relaxation and the theory of mixing time for finding the fast queuing policies that drive the distribution of packets in a queue to a given target stationary distribution. It is argued that a target stationary distribution can be used to characterize various performance metrics of network flow. Thus, finding a fast queuing policy that produces a given target stationary distribution is vital in achieving some given objectives. In addition, we show how to augment the basic proposed framework in order to obtain a queuing policy that produces ε-approximation to the target distribution with even faster convergence time. This fast adaptation is especially useful for networking applications in fast-changing network conditions. Both theory and simulation results are presented to verify our framework

Journal of Telecommunications and Information Technology, 2017, nr 1

kwartalni

Elastic phone : towards detecting and mitigating computation and energy inefficiencies in mobile apps

Mobile devices have become ubiquitous and their ever evolving capabilities are bringing them closer to personal computers. Nonetheless, due to their mobility and small size factor constraints, they still present many hardware and software challenges. Their limited battery life time has led to the design of mobile networks that are inherently different from previous networks (e.g., wifi) and more restrictive task scheduling. Additionally, mobile device ecosystems are more susceptible to the heterogeneity of hardware and from conflicting interests of distributors, internet service providers, manufacturers, developers, etc. The high number of stakeholders ultimately responsible for the performance of a device, results in an inconsistent behavior and makes it very challenging to build a solution that improves resource usage in most cases. The focus of this thesis is on the study and development of techniques to detect and mitigate computation and energy inefficiencies in mobile apps. It follows a bottom-up approach, starting from the challenges behind detecting inefficient execution scheduling by looking only at apps’ implementations. It shows that scheduling APIs are largely misused and have a great impact on devices wake up frequency and on the efficiency of existing energy saving techniques (e.g., batching scheduled executions). Then it addresses many challenges of app testing in the dynamic analysis field. More specifically, how to scale mobile app testing with realistic user input and how to analyze closed source apps’ code at runtime, showing that introducing humans in the app testing loop improves the coverage of app’s code and generated network volume. Finally, using the combined knowledge of static and dynamic analysis, it focuses on the challenges of identifying the resource hungry sections of apps and how to improve their execution via offloading. There is a special focus on performing non-intrusive offloading transparent to existing apps and on in-network computation offloading and distribution. It shows that, even without a custom OS or app modifications, in-network offloading is still possible, greatly improving execution times, energy consumption and reducing both end-user experienced latency and request drop rates. It concludes with a real app measurement study, showing that a good portion of the most popular apps’ code can indeed be offloaded and proposes future directions for the app testing and computation offloading fields.Los dispositivos móviles se han tornado omnipresentes y sus capacidades están en constante evolución acercándolos a los computadoras personales. Sin embargo, debido a su movilidad y tamaño reducido, todavía presentan muchos desafíos de hardware y software. Su duración limitada de batería ha llevado al diseño de redes móviles que son inherentemente diferentes de las redes anteriores y una programación de tareas más restrictiva. Además, los ecosistemas de dispositivos móviles son más susceptibles a la heterogeneidad de hardware y los intereses conflictivos de las entidades responsables por el rendimiento final de un dispositivo. El objetivo de esta tesis es el estudio y desarrollo de técnicas para detectar y mitigar las ineficiencias de computación y energéticas en las aplicaciones móviles. Empieza con los desafíos detrás de la detección de planificación de ejecución ineficientes, mirando sólo la implementación de las aplicaciones. Se muestra que las API de planificación son en gran medida mal utilizadas y tienen un gran impacto en la frecuencia con que los dispositivos despiertan y en la eficiencia de las técnicas de ahorro de energía existentes. A continuación, aborda muchos desafíos de las pruebas de aplicaciones en el campo de análisis dinámica. Más específicamente, cómo escalar las pruebas de aplicaciones móviles con una interacción realista y cómo analizar código de aplicaciones de código cerrado durante la ejecución, mostrando que la introducción de humanos en el bucle de prueba de aplicaciones mejora la cobertura del código y el volumen de comunicación de red generado. Por último, combinando la análisis estática y dinámica, se centra en los desafíos de identificar las secciones de aplicaciones con uso intensivo de recursos y cómo mejorar su ejecución a través de la ejecución remota (i.e.,"offload"). Hay un enfoque especial en el "offload" no intrusivo y transparente a las aplicaciones existentes y en el "offload"y distribución de computación dentro de la red. Demuestra que, incluso sin un sistema operativo personalizado o modificaciones en la aplicación, el "offload" en red sigue siendo posible, mejorando los tiempos de ejecución, el consumo de energía y reduciendo la latencia del usuario final y las tasas de caída de solicitudes de "offload". Concluye con un estudio real de las aplicaciones más populares, mostrando que una buena parte de su código puede de hecho ser ejecutado remotamente y propone direcciones futuras para los campos de "offload" de aplicaciones

Elastic phone : towards detecting and mitigating computation and energy inefficiencies in mobile apps

Mobile devices have become ubiquitous and their ever evolving capabilities are bringing them closer to personal computers. Nonetheless, due to their mobility and small size factor constraints, they still present many hardware and software challenges. Their limited battery life time has led to the design of mobile networks that are inherently different from previous networks (e.g., wifi) and more restrictive task scheduling. Additionally, mobile device ecosystems are more susceptible to the heterogeneity of hardware and from conflicting interests of distributors, internet service providers, manufacturers, developers, etc. The high number of stakeholders ultimately responsible for the performance of a device, results in an inconsistent behavior and makes it very challenging to build a solution that improves resource usage in most cases. The focus of this thesis is on the study and development of techniques to detect and mitigate computation and energy inefficiencies in mobile apps. It follows a bottom-up approach, starting from the challenges behind detecting inefficient execution scheduling by looking only at apps’ implementations. It shows that scheduling APIs are largely misused and have a great impact on devices wake up frequency and on the efficiency of existing energy saving techniques (e.g., batching scheduled executions). Then it addresses many challenges of app testing in the dynamic analysis field. More specifically, how to scale mobile app testing with realistic user input and how to analyze closed source apps’ code at runtime, showing that introducing humans in the app testing loop improves the coverage of app’s code and generated network volume. Finally, using the combined knowledge of static and dynamic analysis, it focuses on the challenges of identifying the resource hungry sections of apps and how to improve their execution via offloading. There is a special focus on performing non-intrusive offloading transparent to existing apps and on in-network computation offloading and distribution. It shows that, even without a custom OS or app modifications, in-network offloading is still possible, greatly improving execution times, energy consumption and reducing both end-user experienced latency and request drop rates. It concludes with a real app measurement study, showing that a good portion of the most popular apps’ code can indeed be offloaded and proposes future directions for the app testing and computation offloading fields.Los dispositivos móviles se han tornado omnipresentes y sus capacidades están en constante evolución acercándolos a los computadoras personales. Sin embargo, debido a su movilidad y tamaño reducido, todavía presentan muchos desafíos de hardware y software. Su duración limitada de batería ha llevado al diseño de redes móviles que son inherentemente diferentes de las redes anteriores y una programación de tareas más restrictiva. Además, los ecosistemas de dispositivos móviles son más susceptibles a la heterogeneidad de hardware y los intereses conflictivos de las entidades responsables por el rendimiento final de un dispositivo. El objetivo de esta tesis es el estudio y desarrollo de técnicas para detectar y mitigar las ineficiencias de computación y energéticas en las aplicaciones móviles. Empieza con los desafíos detrás de la detección de planificación de ejecución ineficientes, mirando sólo la implementación de las aplicaciones. Se muestra que las API de planificación son en gran medida mal utilizadas y tienen un gran impacto en la frecuencia con que los dispositivos despiertan y en la eficiencia de las técnicas de ahorro de energía existentes. A continuación, aborda muchos desafíos de las pruebas de aplicaciones en el campo de análisis dinámica. Más específicamente, cómo escalar las pruebas de aplicaciones móviles con una interacción realista y cómo analizar código de aplicaciones de código cerrado durante la ejecución, mostrando que la introducción de humanos en el bucle de prueba de aplicaciones mejora la cobertura del código y el volumen de comunicación de red generado. Por último, combinando la análisis estática y dinámica, se centra en los desafíos de identificar las secciones de aplicaciones con uso intensivo de recursos y cómo mejorar su ejecución a través de la ejecución remota (i.e.,"offload"). Hay un enfoque especial en el "offload" no intrusivo y transparente a las aplicaciones existentes y en el "offload"y distribución de computación dentro de la red. Demuestra que, incluso sin un sistema operativo personalizado o modificaciones en la aplicación, el "offload" en red sigue siendo posible, mejorando los tiempos de ejecución, el consumo de energía y reduciendo la latencia del usuario final y las tasas de caída de solicitudes de "offload". Concluye con un estudio real de las aplicaciones más populares, mostrando que una buena parte de su código puede de hecho ser ejecutado remotamente y propone direcciones futuras para los campos de "offload" de aplicaciones.Postprint (published version

An Internet based multimedia infrastructure for collaborative engineering

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2000.Includes bibliographical references (leaves 129-131).The evolution of computer based collaborative environments has resulted in easier and more economical design efforts among geographically distributed design teams. Most of today's internet based collaborative applications allow people that are geographically dispersed to meet with each other using their computers and work together without actually having to travel. A prototype system was developed by taking two tactical planning applications and incorporating them into the collaboration model employed by CAIRO (Collaborative Agent Interaction control and synchROnization). This system was developed based on the collaboration infrastructure that was developed as a part of the Da-Vinci Society Initiative at MIT. The main focus of this research lies in the formalization of a multi-media based architecture that supplements the existing collaboration infrastructure. This architecture lays the groundwork for development of a robust collaboration system that incorporates audio/video conferencing, speech recognition and synthesis and three-dimensional virtual meeting environments in order to facilitate efficient collaboration.by Padmanabha N. Vedam.S.M

Task assignment in server farms under realistic workload conditions

Server farms have become very popular in recent years since they effectively address the problem of large delays, a common problem faced by many organisations whose systems receive high volumes of traffic. Recently, there has been a wide use of these server farms in two main areas, namely, Web hosting and scientific computing. The performance of such server farms is highly reliant on the underlying task assignment policy, a specific set of rules that defines how the incoming tasks are assigned to and processed at hosts. The aim of a task assignment policy is to optimise certain performance criteria such as the expected waiting time and slowdown. One of the key factors that affect the performance of these policies is the service time distribution of tasks. There is extensive evidence indicating that the service times of modern computer workloads closely follow heavy-tailed distributions that possess high variance. However, in certain environments, the service time distributions of tasks are unknown. Imposing parametric assumptions in such cases can lead to inaccurate and unreliable inferences. Considerable efforts have been made in recent years to devise efficient policies. Although these policies perform well under specific workload conditions, they have several major limitations. These include the assumption of known service times, inability to efficiently assign tasks in time sharing server farms, poor performance under changing workload conditions and poor performance under multiple server farms. This thesis aims at proposing novel task assignment policies for assigning tasks in server farms under two main classes of realistic workload conditions, namely, the heavy-tailed and arbitrary service time distributions. Arbitrary service time distributions are assumed, for cases where the underlying service time distribution of tasks is unknown. First we investigate ways to optimise the performance in a time-sharing server. We concentrate on a particular scheduling policy called multi-level time sharing policy (MLTP). We provide an extensive performance analysis of MTLP and show that MLTP can result in significant performance improvements under certain traffic conditions. Second we investigate how to improve the performance in time sharing server farms using MLTP. Three task assignment policies are proposed for time sharing server farms. Third we investigate how to design efficient task assignment policies to assign tasks in multiple server farms. We propose MCTPM which is based on a multi-tier host architecture. MCTPM supports preemptive task migration and it controls the traffic flow into server farms via a global dispatching device so as to optimise the performance. Finally, we investigate ways to design adaptive task assignment policies that make no assumptions regarding the underlying service time distribution of tasks. We propose a novel task assignment policy, called ADAPT-POLICY, which is based on a set of static-based task assignment policies. ADAPT-POLICY is based on a set of policies for the server farm and it adaptively changes the task assignment policy to suit the most recent traffic conditions. The experimental performance analysis of ADAPT-POLICY shows that ADAPT-POLICY outperforms other policies under a range of traffic conditions