In HTTP/1.1, it is necessary for the client to request an object (e.g. an image in a page) in order for the server to send it, even if the server knows in advance what the client will need. Server Push is a feature introduced in HTTP/2 that promises to improve page load times (PLT) by having the server push content to the browser in advance. In this paper, we investigate the benefits and challenges of using Server Push on mobile devices. We first examine whether pushing all content or just the CSS and Javascript files performs better, and find the former leads to much better web performance. Also, we find that sites making use of domain sharding or which otherwise have content divided across many servers do not benefit much from Server Push, a major challenge for Server Push going forward. Network performance characteristics also play a major role. Server Push is especially effective at improving performance at high loss rates (16% median PLT reduction with a 2% loss rate) and high latencies (14% PLT reduction with 100 ms latency), and has little benefit for high-speed Ethernet connections. This motivates its use on mobile devices, although we also find the limited processing power of these devices limits the benefits of Server Push. Server Push also offers modest energy benefits, with energy savings of 9% on LTE for one device. Overall, Server Push is a promising approach for improving web performance in mobile networks, but there are a number of challenges in achieving the full benefits of Server Push.

Energy consumption due to network traffic on mobile devices continues to be a significant concern. We examine a range of excessive energy consumption problems caused by background network traffic through a two-year user study, and also validate these findings through in-lab testing of the most recent versions of major mobile apps. We discover a new energy consumption problem where foreground network traffic persists after switching from the foreground to the background, leading to unnecessary energy and data drain. Furthermore, while we find some apps have taken steps to improve the energy impact of periodic background traffic, energy consumption differences of up to an order of magnitude exist between apps with near-identical functionality. Finally, by examining how apps are used in the wild, we find that some apps continue to generate unneeded traffic for days when the app is not being used, and in some cases this wasted traffic is responsible for a majority of the app's network energy overhead. We propose that these persistent, widespread and varied sources of excessive energy consumption in popular apps should be addressed through new app management tools that tailor network activity to user interaction patterns.

Smartphones have become increasingly prevalent and important in our daily lives. To meet users' expectations about the Quality of Experience (QoE) of mobile applications (apps), it is essential to obtain a comprehensive understanding of app QoE and identify the critical factors that affect it. However, effectively and systematically studying the QoE of popular mobile apps such as Facebook and YouTube still remains a challenging task, largely due to a lack of a controlled and reproducible measurement methodology, and limited insight into the complex multi-layer dynamics of the system and network stacks.

To conserve power while ensuring good performance on resource-constrained mobile devices, devices transition between different Radio Resource Control (RRC) states in response to network traffic and according to parameters specific to network operators. As RRC states significantly affect application power consumption and performance, it is important to understand how RRC state timers interact with network traffic patterns. In this paper, we show that the impact of RRC states on performance is significantly more complex and diverse than found in previous work. To do so, we introduce an open-source tool that allows the impact of RRC states on network and application performance to be measured in a robust and accurate manner on unmodified user devices, and deploy the tool in 23 countries around the world to test a broad range of cellular network technologies. We detect previously unknown performance problems which increase network latencies by up to several seconds and for LTE, can increase packet losses by an order of magnitude. Through an in-depth cross-layer analysis of several carriers, we examine the lower-layer causes of these problems. We determine that the highly complex state transitions of certain carriers, and in particular poor interactions between state demotions and network traffic, can lead to substantial, unexpected latencies.

Mobilyzer is an open-source network measurement library that coordinates network measurement tasks among different applications, facilitates measurement task design, and allows for more effective measurement task management than in existing standalone approaches. Unifying various network tasks into one framework greatly simplifies the problem of developing, deploying and managing measurement tasks which may otherwise interfere with one another. An intelligent scheduler, coordinated by a central server, dynamically schedules tasks to run in the background, preserving the user's battery life and respecting limits set by the user on task frequency and data consumption. We will demo MobiPerf, an open-source mobile network measurement tool built using the Mobilyzer library. MobiPerf collects a wide range of network performance data, ranging from the latency and throughput measurements common in existing client-based measurement frameworks, to HTTP loading times for specific URLs, to inferring RRC state configuration parameters and their impact on performance. We will also demo an interface for viewing a large, open dataset of performance data from around the world collected by MobiPerf.

Although Android's permission system is intended to allow users to make informed decisions about their privacy, it is often ineffective at conveying meaningful, useful information on how a user's privacy might be impacted by using an application. We present an alternate approach to providing users the knowledge needed to make informed decisions about the applications they install. First, we create a knowledge base of mappings between API calls and fine-grained privacy-related behaviors. We then use this knowledge base to produce, through static analysis, high-level behavior profiles of application behavior. We have analyzed almost 80,000 applications to date and have made the resulting behavior profiles available both through an Android application and online. Nearly 1500 users have used this application to date. Based on 2782 pieces of application-specific feedback, we analyze users' opinions about how applications affect their privacy and demonstrate that these profiles have had a substantial impact on their understanding of those applications. We also show the benefit of these profiles in understanding large-scale trends in how applications behave and the implications for user privacy.