Showing papers by "Luca De Cicco published in 2016"

Analysis and design of the google congestion control for web real-time communication (WebRTC)

Abstract: Video conferencing applications require low latency and high bandwidth. Standard TCP is not suitable for video conferencing since its reliability and in order delivery mechanisms induce large latency. Recently the idea of using the delay gradient to infer congestion is appearing again and is gaining momentum. In this paper we present an algorithm that is based on estimating through a Kalman filter the end-to-end one way delay variation which is experienced by packets traveling from a sender to a destination. This estimate is compared to an adaptive threshold to dynamically throttle the sending rate. The control algorithm has been implemented over the RTP/RTCP protocol and is currently used in Google Hangouts and in the Chrome WebRTC stack. Experiments have been carried out to evaluate the algorithm performance in the case of variable link capacity, presence of heterogeneous or homogeneous concurrent traffic, and backward path traffic.

Measuring the Quality of Experience of Web users

Abstract: Measuring quality of Web users experience (WebQoE) faces the following trade-off. On the one hand, current practice is to resort to metrics, such as the document completion time (onLoad), that are simple to measure though knowingly inaccurate. On the other hand, there are metrics, like Google’s SpeedIndex, that are better correlated with the actual user experience, but are quite complex to evaluate and, as such, relegated to lab experiments. In this paper, we first provide a comprehensive state of the art on the metrics and tools available for WebQoE assessment. We then apply these metrics to a representative dataset (the Alexa top-100 webpages) to better illustrate their similarities, differences, advantages and limitations. We next introduce novel metrics, inspired by Google’s SpeedIndex, that (i) offer significant advantage in terms of computational complexity, (ii) while maintaining a high correlation with the SpeedIndex at the same time. These properties makes our proposed metrics highly relevant and of practical use.

Revisiting a Watermark-Based Detection Scheme to Handle Cyber-Physical Attacks

Abstract: We address detection of attacks against cyber-physical systems. Cyber-physical systems are industrial control systems upgraded with novel computing, communication and interconnection capabilities. In this paper we reexamine the security of a detection scheme proposed by Mo and Sinopoli (2009) and Mo et al. (2015). The approach complements the use of Kalman filters and linear quadratic regulators, by adding an authentication watermark signal for the detection of integrity attacks. We show that the approach only detects cyber adversaries, i.e., attackers with the ability to eavesdrop information from the system, but that do not attempt to acquire any knowledge about the system model itself. The detector fails at covering cyber-physical adversaries, i.e., attackers that, in addition to the capabilities of the cyber adversary, are also able to infer the system model to evade the detection. We discuss an enhanced scheme, based on a multi-watermark authentication signal, that properly detects the two adversary models.

Event-Triggered Watermarking Control to Handle Cyber-Physical Integrity Attacks

Abstract: The use of control-theoretic solutions to detect attacks against cyber-physical systems is a growing area of research. Traditional literature proposes the use of control strategies to retain, f.i., satisfactory closed-loop performance, as well as safety properties, when a communication network connects the distributed components of a physical system (e.g., sensors, actuators, and controllers). However, the adaptation of these strategies to handle security incidents, is an ongoing challenge. In this paper, we analyze the use of a watermark-based detector that handles integrity attacks. We show that (1) the detector is able to work properly under the presence of adversaries using non-parametric methods to escape detection; but (2) it fails at detecting adversaries using parametric identification methods to escape detection. We propose a new strategy that complements the watermark-based detector in order to detect both adversaries. We validate the detection efficiency of the new strategy via numeric simulations.

Making Google Congestion Control robust over Wi-Fi networks using packet grouping

Abstract: Google congestion control (GCC) has been proposed for the case of delay sensitive traffic (i.e. video-conference) in the WebRTC framework. In this paper we analyze the effect of wireless channel outages on the GCC. We have observed that, when a channel outage ends, there are packets that arrive at the receiver as a burst. This behavior impairs the delay-based controller employed by GCC, resulting in throughput degradation. We propose a solution to make GCC robust with respect to channel outages. In particular, by grouping packets that arrive in a burst, the delay-based controller avoids to misinterpret a burst as network congestion. In order to prove the effectiveness of the proposed solution we have carried out a trace-driven experimental evaluation in a loaded Wi-Fi scenario.

Congestion control for real-time communications: A comparison between NADA and GCC

Abstract: Congestion control for Web real-time communication (WebRTC) is a hot topic currently addressed at the IETF. Differently from congestion control for TCP, congestion control for WebRTC not only aims at containing packet losses, but also aims at minimizing queuing delays to provide interactivity. In this paper we describe two algorithms under discussion at IETF: Network Assisted Dynamic Adaptation (NADA) proposed by Cisco Systems and Google Congestion Control (GCC) proposed by Google. A performance comparison in a simulation environment is carried out. Results show that GCC exhibits slow convergence whereas NADA exhibits a remarkable oscillating behavior.

A hybrid model of adaptive video streaming control systems

Abstract: Video streaming traffic over the Internet has significantly grown in the recent years. Adaptive video streaming control systems are employed to provide the best user experience given the user device and the network available bandwidth. The control goal is to maximize the video bitrate while avoiding playback interruptions. In this paper, we present a complete and accurate model of a generic adaptive streaming control system in the form of a hybrid dynamical system. The model describes all the system features, differently from previous models making the fluid-flow approximation, and allows to rigorously design video streaming controllers whose performance can be analytically assessed. The high accuracy of the model has been assessed by comparing numerical simulations to experimental data obtained through real network experiments. Given its accuracy and low computation cost, the proposed model provides a promising alternative to network experiments in order to aid the design and evaluation of adaptive video streaming systems.

A Control-Theoretic Analysis of Low-Priority Congestion Control Reprioritization under AQM

Abstract: Recently, a negative interplay has been shown to arise when scheduling/Active Queue Management (AQM) techniques and low-priority congestion control protocols are used together; namely, AQM resets the relative level of priority among congestion control protocols. This work explores this issue by carrying out a control-theoretic analysis of the dynamical system to prove some fundamental properties that fully characterize the reprioritization phenomenon. In particular, (i) we provide the closed-form solution of the equilibrium in the open loop (i.e., fixing a target loss probability p); (ii) we provide a stability analysis and a characterization of the reprioritization phenomenon when closing the loop with AQM (i.e., that dynamically adjusts the system loss probability). Our results are important as the characterization of the reprioritization phenomenon is not only quantitatively accurate for the specific protocols and AQM considered but also qualitatively accurate for a broader range of congestion control protocol and AQM combinations. Finally, while we find a sufficient condition to avoid the reprioritization phenomenon, we also show, at the same time, such conditions to be likely impractical: Therefore, we propose a simple and practical system-level solution that is able to reinstate priorities among protocols.