Invited Abstract: A Simulation Package for Energy Consumption of Content Delivery Networks (CDNs)

Content Delivery Networks (CDNs) are becoming an integral part of the future generation Internet. Traditionally, these networks have been designed with the goals of traffic offload and the improvement of users' quality of experience (QoE), but the energy consumption is also becoming an indispensable design factor for CDNs to be a sustainable solution. To study and improve the CDN architectures using this new design metric, we are planning to develop a generic and flexible simulation package in OMNet++. This package is aimed to render a holistic view about the CDN energy consumption behaviour by incorporating the state-of-the-art energy consumption models proposed for the individual elements of CDNs (e.g. servers, routers, wired and wireless links, wireless devices, etc.) and for the various Internet contents (web pages, files, streaming video, etc.).Comment: Published in: A. F\"orster, C. Minkenberg, G. R. Herrera, M. Kirsche (Eds.), Proc. of the 2nd OMNeT++ Community Summit, IBM Research - Zurich, Switzerland, September 3-4, 2015, arXiv:1509.03284, 201

Energy-Aware WiFi Network Selection via Forecasting Energy Consumption

Covering a wide area by a large number of WiFi networks is anticipated to become very popular with Internet-of-things (IoT) and initiatives such as smart cities. Such network configuration is normally realized through deploying a large number of access points (APs) with overlapped coverage. However, the imbalanced traffic load distribution among different APs affects the energy consumption of a WiFi device if it is associated to a loaded AP. This research work aims at predicting the communication-related energy that shall be consumed by a WiFi device if it transferred some amount of data through a certain selected AP. In this paper, a forecast of the energy consumption is proposed to be obtained using an algorithm that is supported by a mathematical model. Consequently, the proposed algorithm can automatically select the best WiFi network (best AP) that the WiFi device can connect to in order to minimize energy consumption. The proposed algorithm is experimentally validated in a realistic lab setting. The observed performance indicates that the algorithm can provide an accurate forecast to the energy that shall be consumed by a WiFi transceiver in sending some amount of data via a specific AP

Characterizing Multi-radio Energy Consumption in Cellular/Wi-Fi Smartphones

Cellular networks evolved to meet the ever increasing traffic demand by way of offloading mobile traffic to Wi-Fi network elements. Exploiting multi-radio interfaces on a smartphone has recently been examined with regards to heterogeneous bandwidth aggregation and radio switching. However, how a smartphone consumes its energy in driving cellular and Wi-Fi multi-radio interfaces, is not well understood. In this paper, we revealed the energy consumption behavior of 3G cellular and Wi-Fi multi-radio operations of a smartphone. We modified smartphone’s firmware to enable multi-radios operations simultaneously and we performed extensive measurements of multi-radio energy consumption in a real commercial network. From the measured data set, we established a realistic multi-radio energy consumption model and it gave 98% stability from the derived coefficients

The impact of the access point power model on the energy-efficient management of infrastructured wireless LANs

The reduction of the energy footprint of large and mid-sized IEEE 802.11 access networks is gaining momentum. When operating at the network management level, the availability of an accurate power model of the APs becomes of paramount importance, because different detail levels have a non-negligible impact on the performance of the optimisation algorithms. The literature is plentiful of AP power models, and choosing the right one is not an easy task. In this paper we report the outcome of a thorough study on the impact that various inflections of the AP power model have when minimising the energy consumption of the infrastructure side of an enterprise wireless LAN. Our study, performed on several network scenarios and for various device energy profiles, reveals that simple one- and two-component models can provide excellent results in practically all cases. Conversely, employing accurate and detailed power models rarely offers substantial advantages in terms of power reduction, but, on the other hand, makes the solving algorithms much slower to execute

Cutting Wi-Fi Scan Tax for Smart Devices

Today most popular mobile apps and location-based services require near always-on Wi-Fi connectivity (e.g., Skype, Viber, Wi-Fi Finder). The Wi-Fi power drain resulting from frequent Wi-Fi active scans is undermining the battery performance of smart devices and causing users to remove apps or disable important services. We collectively call this the scan tax problem. The main reason for this problem is that the main processor has to be active during Wi-Fi active scans and hence consumes a significant and disproportionate amount of energy during scan periods. We propose a simple and effective architectural change, where the main processor periodically computes an SSID list and scan parameters (i.e. scan interval, timeout) taking into account user mobility and behavior (e.g. walking); allowing scan to be offloaded to the Wi-Fi radio. We design WiScan, a complete system to realize scan offloading, and implement our system on the Nexus 5. Both our prototype experiments and trace-driven emulations demonstrate that WiScan achieves 90%+ of the maximal connectivity (connectivity that the existing Wi-Fi scan mechanism could achieve with 5 seconds scan interval), while saving 50-62% energy for seeking connectivity (the ratio between the Wi-Fi connected duration and total time duration) compared to existing active scan implementations. We argue that our proposed shift not only significantly reduces the scan tax paid by users, but also ultimately leads to ultra-low power, always-on Wi-Fi connectivity enabling a new class of context-aware apps to emerge

Analysis and optimal configuration of distributed opportunistic scheduling techniques in wireless networks

The phenomenon of fading in wireless communications has traditionally been considered as a source of unreliability that needs to be mitigated. In contrast, Opportunistic Scheduling (OS) techniques exploit quick channel quality oscillations in fading links, during the assignment of transmission opportunities, to improve the performance of wireless networks. While centralized mechanisms rely on a central entity with global knowledge, Distributed Opportunistic Scheduling (DOS) techniques have recently been proposed to work in distributed networks, i.e., where either such a central entity is not available, or the communication overhead to feed timely information to this central entity is prohibitive. With DOS, each station contends for the channel with a certain access probability. If a contention is successful, the station measures the channel conditions and transmits if the channel quality is above a certain threshold. Otherwise, the station does not use the transmission opportunity, allowing all stations to recontend. Given the fact that different stations, in different time instances, experience different channel conditions, it is likely that the channel is used by a link with better conditions, improving overall performance. In this thesis we first propose ADOS, an adaptive mechanism that drives the system to an optimal allocation of resources in terms of proportional fairness. We show that this mechanism outperforms previous approaches, particularly in scenarios with non-saturated stations (that do not always have data to transmit). The distributed nature of DOS makes it particularly vulnerable to selfish users that seek to maximize their own performance at the expense of those that cooperate for the common welfare. We thus design a punishing mechanism, namely DOC, that (i) drives the system to the optimal point of operation when all stations follow the protocol, and (ii) removes any potential gain by deviating from it (and thus, the incentive to misbehave). Finally, we propose a novel allocation criterion, namely the EF criterion, to balance between the most energy-eficient configuration (where all resources are given to the most energy e cient devices) and the throughput-optimal allocation (where all devices evenly share the resources regardless of their power consumption). Due to the lack of models that accurately predict the power consumption behavior of wireless devices, we perform a thorough experimental study to devise a power consumption model that completes existing literature. Finally, we apply these findings to design an EF-optimal strategy in DOS networks. --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------El fenómeno de "fading" o desvanecimiento en comunicaciones inalámbricas se ha considerado tradicionalmente como una fuente de problemas de fiabilidad que debe ser mitigada. En contraste, las técnicas de asignación de recursos oportunistas aprovechan las oscilaciones en la calidad de enlaces para mejorar el rendimiento global. Mientras que los mecanismos centralizados requieren una entidad central con información global, recientemente se han propuesto técnicas oportunistas distribuidas (DOS, por sus siglas en inglés) para operar en redes donde dicha entidad no está disponible, o donde el coste en la comunicación para proporcionarle información puntual es prohibitivo. Con DOS, cada estación contiende por el canal con una cierta probabilidad. Si la contienda resulta exitosa, la estación mide la calidad del canal y transmite si ésta supera un cierto umbral. De lo contrario, la estación no aprovecha esa oportunidad para transmitir, permitiendo a todas las estaciones contender de nuevo. Dado que estaciones diferentes, en distintas instancias de tiempo, experimentan diferentes condiciones de canal, es probable que un enlace con mejores condiciones use el canal, mejorando el rendimiento global. En esta tesis proponemos primero ADOS, un mecanismo adaptativo que lleva al sistema a un reparto óptimo de los recursos en términos de equidad proporcional. Mostramos que este mecanismo supera el rendimiento de trabajos previos, particularmente en escenarios con estaciones no saturados (que no siempre tienen datos que transmitir). La naturaleza distribuida de DOS lo hace particularmente vulnerable a usuarios egoístas que buscan maximizar su rendimiento a expensas de aquellos que cooperan por el bien común. Así, diseñamos un mecanismo, llamado DOC, que (i) optimiza el rendimiento si todos los nodos obedecen el protocolo, y (ii) elimina cualquier posible beneficio por desviarse del mismo (y así, el incentivo a no cooperar). Finalmente, proponemos un nuevo criterio de asignación de recursos, llamado EF, que supone un compromiso entre la configuración más eficiente energéticamente (donde todos los recursos se asignan a los nodos más eficientes) y una asignación donde todos comparten de forma equitativa los recursos sin tener en cuenta su consumo. Dada la falta de modelos para predecir de forma precisa el consumo de dispositivos inalámbricos, llevamos a cabo un estudio experimental que resulta en un modelo energético que completa a la literatura existente. Finalmente, aplicamos lo anterior para diseñar una estrategia que optimiza EF en redes basadas en DOS