Les défis de l'émulation Wi-Fi à base des traces

Wi-Fi link is unpredictable and it has never been easy to measure it perfectly; there is always bound to be some bias. As wireless becomes the medium of choice, it is useful to capture Wi-Fi traces in order to evaluate, tune, and adapt the different applications and protocols. Several methods have been used for the purpose of experimenting with different wireless conditions: simulation, experimentation, and trace-driven emulation. In this paper, we argue that trace-driven emulation is the most favourable approach. In the absence of a trace-driven emulation tool for Wi-Fi, we evaluate the state-of-the-art trace driven emulation tool for Cellular networks and we identify issues for Wi-Fi: interference with concurrent traffic, interference with its own traffic if measurements are done on both uplink and downlink simultaneously , and packet loss. We provide a solid argument as to why this tool falls short from effectively capturing Wi-Fi traces. The outcome of our analysis guides us to propose a number of suggestions on how the existing tool can be tweaked to accurately capture Wi-Fi traces.La liaison Wi-Fi est imprévisible et il n'a jamais été facile de la mesurer parfaitement ; il y a toujours un risque de biais. Comme le sans fil devient le moyen de communication de choix, il est utile de capturer les traces Wi-Fi afin d'évaluer, de régler et d'adapter les différentes applications et protocoles. Plusieurs méthodes ont été utilisées pour expérimenter différentes conditions sans fil : la simulation, l'expérimentation et l'émulation de traces. Dans cet article, nous soutenons que l'émulation pilotée par les traces est l'approche la plus favorable. En l'absence d'un outil d'émulation piloté par trace pour le Wi-Fi, nous évaluons l'outil d'émulation piloté par trace de pointe pour les réseaux cellulaires et nous identifions les problèmes pour le Wi-Fi : interférence avec le trafic concurrent, interférence avec son propre trafic si les mesures sont effectuées simultanément sur la liaison montante et la liaison descendante, et perte de paquets. Nous fournissons un argument solide pour expliquer pourquoi cet outil ne parvient pas à capturer efficacement les traces Wi-Fi. Le résultat de notre analyse nous guide pour proposer un certain nombre de suggestions sur la manière dont l'outil existant peut être modifié pour capturer avec précision les traces Wi-Fi

ABC: A Simple Explicit Congestion Controller for Wireless Networks

We propose Accel-Brake Control (ABC), a simple and deployable explicit congestion control protocol for network paths with time-varying wireless links. ABC routers mark each packet with an "accelerate" or "brake", which causes senders to slightly increase or decrease their congestion windows. Routers use this feedback to quickly guide senders towards a desired target rate. ABC requires no changes to header formats or user devices, but achieves better performance than XCP. ABC is also incrementally deployable; it operates correctly when the bottleneck is a non-ABC router, and can coexist with non-ABC traffic sharing the same bottleneck link. We evaluate ABC using a Wi-Fi implementation and trace-driven emulation of cellular links. ABC achieves 30-40% higher throughput than Cubic+Codel for similar delays, and 2.2X lower delays than BBR on a Wi-Fi path. On cellular network paths, ABC achieves 50% higher throughput than Cubic+Codel

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

Optimized Live 4K Video Multicast

4K videos are becoming increasingly popular. However, despite advances in wireless technology, streaming 4K videos over mmWave to multiple users is facing significant challenges arising from directional communication, unpredictable channel fluctuation and high bandwidth requirements. This paper develops a novel 4K layered video multicast system. We (i) develop a video quality model for layered video coding, (ii) optimize resource allocation, scheduling, and beamforming based on the channel conditions of different users, and (iii) put forward a streaming strategy that uses fountain code to avoid redundancy across multicast groups and a Leaky-Bucket-based congestion control. We realize an end-to-end system on commodity-off-the-shelf (COTS) WiGig devices. We demonstrate the effectiveness of our system with extensive testbed experiments and emulation

Cutting Through the Complexity of Reverse Engineering Embedded Devices

Performing security analysis of embedded devices is a challenging task. They present many difficulties not usually found when analyzing commodity systems: undocumented peripherals, esoteric instruction sets, and limited tool support. Thus, a significant amount of reverse engineering is almost always required to analyze such devices. In this paper, we present Incision, an architecture and operating-system agnostic reverse engineering framework. Incision tackles the problem of reducing the upfront effort to analyze complex end-user devices. It combines static and dynamic analyses in a feedback loop, enabling information from each to be used in tandem to improve our overall understanding of the firmware analyzed. We use Incision to analyze a variety of devices and firmware. Our evaluation spans firmware based on three RTOSes, an automotive ECU, and a 4G/LTE baseband. We demonstrate that Incision does not introduce significant complexity to the standard reverse engineering process and requires little manual effort to use. Moreover, its analyses produce correct results with high confidence and are robust across different OSes and ISAs

Developing the Transistor and E-Business Using Era

The improvement of Smalltalk has improved web browsers, and current trends suggest that the construction of expert systems will soon emerge. In our research, authors prove the improvement of sensor networks, which embodies the structured principles of steganography [25, 25, 6]. In this position paper, we argue that despite the fact that the Internet can be made interactive, symbiotic, and flexible, object-oriented languages and Web services are entirely incompatible