MultiNets is a system supporting seamless switch-over between wireless interfaces on mobile devices in real-time. MultiNets is configurable to run in three different modes: (i) Energy Saving mode --for choosing the interface that saves the most energy based on the condition of the device, (ii) Offload mode --for offloading data traffic from the cellular to WiFi network, and (iii) Performance mode --for selecting the network for the fastest data connectivity. MultiNets also provides a powerful API that gives the application developers: (i) the choice to select a network interface to communicate with a specific server, and (ii) the ability to simultaneously transfer data over multiple network interfaces. MultiNets is modular, easily integrable, lightweight, and applicable to various mobile operating systems. We implement MultiNets on Android devices as a show case. MultiNets does not require any extra support from the network infrastructure and runs existing applications transparently. To evaluate MultiNets, we first collect data traces from 13 actual Android smartphone users over three months. We then use the collected traces to show that, by automatically switching to WiFi whenever it is available, MultiNets can offload on average 79.82% of the data traffic. We also illustrate that, by optimally switching between the interfaces, MultiNets can save on average 21.14 KJ of energy per day, which is equivalent to 27.4% of the daily energy usage. Using our API, we demonstrate that a video streaming application achieves 43--271% higher streaming rate when concurrently using WiFi and 3G interfaces. We deploy MultiNets in a real-world scenario and our experimental results show that depending on the user requirements, it outperforms the state-of-the-art Android system either by saving up to 33.75% energy, achieving near-optimal offloading, or achieving near-optimal throughput while substantially reducing TCP interruptions due to switching.

Is it possible to migrate TCP/IP flows between different networks on modern mobile devices without infrastructure support or protocol changes? To answer this question, we make three research contributions: 1) We report a comprehensive characterization of IP traffic on 27 iPhone 3GS users for three months. 2) Driven by these findings, we devise two simple, effective, and easily deployable system mechanisms to support seamless flow migration without network support, and extensively evaluate their effectiveness using our field collected traces of real-life usage. Wait-n-Migrate leverages the fact that most flows are short lived. It establishes new flows on newly available networks but allows preexisting flows on the old network to terminate naturally. Resumption Agent takes advantage of the resumption functionality of modern protocols to securely resume flows without application intervention. Combined, they provide an unprecedented opportunity to immediately deploy policies that leverage multiple networks to improve the performance, efficiency, and connectivity of mobile devices. 3) We report an iPhone-based implementation of these system mechanisms and demonstrate their overhead to be negligible. Furthermore, we employ a sample switching policy, AutoSwitch, to demonstrate their performance. Through traces and field measurements, we show that AutoSwitch reduces user disruptions by an order of magnitude.

Today's mobile Internet is heavily overloaded by the increasing demand and capability of mobile devices, in particular, multimedia traffic. However, not all traffic is created equal, and a large portion of multimedia contents on the mobile Internet is delay tolerant. We study the problem of capitalizing the content transfer opportunities under better network conditions via postponing the transfers without violating the user-specified deadlines. We propose a new framework called SmartTransfer, which offers a unified content transfer interface to mobile applications. We also develop two scheduling algorithms to opportunistically schedule the content transfers. Via extensive trace-driven simulations, we show that our algorithms outperform a baseline scheduling algorithm by far: up to 17 times improvement in upload throughput and/or at most 20 dBm boost in signal strength. The simulation results also reveal various tradeoff between the two proposed scheduling algorithms. We have implemented our framework and one of the scheduling algorithms on Android, to demonstrate their practicality and efficiency.

In this paper we present Multi Nets, a system which is capable of switching between wireless network interfaces on mobile devices in real-time. Multi Nets is motivated by the need of smart phone platforms to save energy, offload data traffic, and achieve higher throughput. We describe the architecture of Multi Nets and demonstrate the methodology to perform switching in Linux based mobile OSes such as Android. Our analysis on mobile data traces collected from real users shows that with real-time switching we can save 27.4% of the energy, offload 79.82% of the data traffic, or achieve 7 times more throughput on average. We deploy Multi Nets in a real world scenario and our experimental results show that depending on the user requirements, it outperforms the state-of-the-art Android system either by saving up to 33.75% energy, or achieving near-optimal offloading, or achieving near-optimal throughput while substantially reducing TCP interruptions due to switching.

Despite the growing popularity of mobile web browsing, the energy consumed by a phone browser while surfing the web is poorly understood. We present an infrastructure for measuring the precise energy used by a mobile browser to render web pages. We then measure the energy needed to render financial, e-commerce, email, blogging, news and social networking sites. Our tools are sufficiently precise to measure the energy needed to render individual web elements, such as cascade style sheets (CSS), Javascript, images, and plug-in objects. Our results show that for popular sites, downloading and parsing cascade style sheets and Javascript consumes a significant fraction of the total energy needed to render the page. Using the data we collected we make concrete recommendations on how to design web pages so as to minimize the energy needed to render the page. As an example, by modifying scripts on the Wikipedia mobile site we reduced by 30% the energy needed to download and render Wikipedia pages with no change to the user experience. We conclude by estimating the point at which offloading browser computations to a remote proxy can save energy on the phone.

In this paper we present PROSE, a system that performs reversible and systematic changes to running Java applications without requiring them to be shut down. PROSE is motivated by scenarios such as hotfixes, online program instrumentation and debugging, and evolution of critical legacy applications. In PROSE, changes to running applications are performed by replacing method bodies. To select which code to replace, PROSE supports matching based on both type information and regular expressions. New code can invoke the method it replaces, facilitating code evolution. Changes are composable, and may be reordered or selectively withdrawn at any time. Furthermore, the dynamic changes are expressed as Java classes rather than through an additional programming language. We describe the architecture of PROSE, the challenges of using aggressive inlining to achieve performance, and use standard benchmarks to demonstrate code performance comparable with, or better than, compile-time systems from the Aspect-Oriented Programming community.

Persistence is a common requirement in many applications. In existing systems, persistence is added to an application at either compile or deployment time by using a variety of mechanisms. In this paper we extend the notion of orthogonal persistence to make it dynamic: persistence becomes not only an orthogonal concern but one that can be added to an application at run-time without interrupting its operations.