Fraida Fund

Not) yet another policy for scalable video delivery to mobile users

In this work, we provide a methodology to analyze optimal adaptation policies for scalable video delivery in mobile environments. Typically, download policies for adaptive video are tuned to very specific system settings. The aim of this work is not to propose a new policy, but instead to understand how the optimal policy changes according to the operating environment and the system characteristics of a mobile video client. Armed with this insight, we can design or adapt policies for SVC adaptive video delivery for a broader range of settings. Using a semi-Markov decision process (SMDP), we find optimal video retrieval policies for a single user, subject to different limits on buffer capacity and different wireless environments. We apply a decision tree classifier to the output of the SMDP to derive simple approximate policies for 55 scenarios and use these to derive high-level rules on the relationship between optimal download policy and the underlying channel settings. For example, we show that the optimal policy is more conservative in slowly varying channels, and becomes more greedy in fast changing channels, and that instantaneous channel state is relevant to the decision-making process only in a setting with a very limited buffer capacity and slow-varying channel.

GENI WiMAX Performance: Evaluation and Comparison of Two Campus Testbeds

In the last few years, there has been an increasing awareness of the need to evaluate new mobile applications and protocols in realistic wireless settings, and platforms such as the GENI WiMAX testbeds have been developed to fulfill this need. However, wireless testbed users have experienced frustration when straightforward usage scenarios do not consistently agree with the high data rates that are advertised by the wireless technology. This work seeks to clarify the performance characteristics of two GENI WiMAX testbeds under various wireless signal conditions and network traffic patterns. By measuring the performance of several popular wireless Internet applications in two very different wireless environments, we gain a deeper understanding of how a researcher may expect the GENI WiMAX platform to behave. Our findings include some counterintuitive results, e.g. that increasing signal quality can reduce application throughput, and that applications using a single TCP flow may achieve as much as 72% less throughput than an application in an identical setting that uses multiple TCP flows. With this work, we hope to help other researchers design realistic experiments on wireless Internet systems, understand the perceived shortcomings of the GENI WiMAX platform, and interpret their experimental results in the context of the wireless setting in which the experiment was conducted.

Resource sharing among mmWave cellular service providers in a vertically differentiated duopoly

With the increasing interest in the use of millimeter wave bands for 5G cellular systems comes renewed interest in resource sharing. Properties of millimeter wave bands such as massive bandwidth, highly directional antennas, high penetration loss, and susceptibility to shadowing, suggest technical advantages to spectrum and infrastructure sharing in millimeter wave cellular networks. However, technical advantages do not necessarily translate to increased profit for service providers, or increased consumer surplus. In this paper, detailed network simulations are used to better understand the economic implications of resource sharing in a vertically differentiated duopoly market for cellular service. The results suggest that resource sharing is less often profitable for millimeter wave service providers compared to microwave cellular service providers, and does not necessarily increase consumer surplus.

More bars, more bang for the buck: Channel-dependent pricing for video delivery to mobile users

A great deal of research energy has been focused on the challenge of delivering high-quality video content to mobile users. In many over-the-top video services, however, the scheduler responsible for channel resource allocation is not aware of content characteristics or playback schedules at end user devices. Therefore, it cannot allocate physical resources in a way that maximizes video quality. For example, it cannot prioritize the transmission of a video frame that is to be displayed within seconds over one whose playback deadline is minutes away. Furthermore, for content that is to be viewed immediately, previous pricing structures that incentivize delaying network use to off-peak hours or WiFi offloading do not apply. To address this issue, we introduce a tiered link quality-dependent data pricing scheme for use together with usage-based pricing in wireless networks. Our pricing model encourages selfish users to prefetch video content during short intervals of good link quality, and use minimal resources when they have a poor link quality. This offers an economic incentive to video consumers to use physical resources more efficiently even with an oblivious scheduler, and leads to better overall video quality for all users in a wireless cell, as well as increased revenue for the wireless service provider.

Implementation of a protocol for cooperative packet recovery over hybrid networks

In this work, we consider the challenge of delivering high-quality multimedia content to users concentrated in a small physical location, e.g., a sports stadium in which fans may view extra video content on their mobile devices. Because each user experiences a different wireless channel condition, it is difficult to deliver this content efficiently to all users. A hybrid network architecture has been proposed that uses a peer to peer exchange of packets over an assistant network to supplement the primary infrastructure network in this scenario. We describe an implementation of this popular technique which may be used in a variety of network environments and applications. In trials on a wireless networking testbed, using WiMAX as the primary network and WiFi as an assistant network, we find that our implementation can recover up to 92% of packets lost over the primary network.

A Framework for Multidimensional Measurements on an Experimental WiMAX Testbed

A major difficulty in the design, study, and implementation of wireless protocols and applications is the multitude of nondeterministic factors (e.g. interference, weather conditions, competing traffic) that can affect their performance. For this reason, testbeds that enable researchers to quantify these influences have become increasingly essential in the wireless research community. The growing sophistication of wireless testbeds and the wide array of services they can provide to researchers have advanced the field tremendously.

Bridging the digital divide between research and home networks

Computer networking testbeds have made it easier for researchers to conduct realistic evaluations of new network protocols or services. However, it is challenging for users to configure testbeds or other experimental networks so that they are representative of typical home broadband links. To address this issue, we have developed a tool with which experimenters can configure links whose characteristics are drawn from a dataset of over 8,000 profiles of home Internet links in the United States, including fiber, cable, DSL, and satellite Internet connections from a range of speed and cost tiers. This paper describes our tool, and explains how it may be used with a variety of experimental platforms. We hope to make it easier for researchers to mimic networks that are representative of a variety of home users, so as to potentially increase the relevance of their experiments to this population.

How bad is the flat earth assumption? Effect of topography on wireless systems

A common simplifying assumption made in wireless simulation and modeling is that the world is flat, i.e. to ignore the effect of the terrain in which the wireless signal propagates. In this paper, we show with empirical measurements from an urban wireless network testbed how the terrain affects the spatial and temporal correlation of the wireless signal, and in turn, the distance or duration over which the wireless signal remains consistent. Furthermore, we suggest that this effect has practical implications for systems that make assumptions about the duration over which wireless signal quality stays roughly the same, such as adaptive transmission schemes or applications that buffer data to smooth over variations in signal quality.

GENI in the Classroom

One of the great successes of GENI has been its use as a remote laboratory by instructors of networking, distributed systems and cloud computing classes. It allows instructors to provide hands-on learning experiences on a real, large-scale network. Reasons for this success include GENI’s ease of use, access to resources such as programmable switches and wireless base stations that are not ordinarily available at most schools, support for collaborative experimentation and ease of recovering from mistakes. The GENI community has created and made available to instructors ready-to-use exercises based on popular networking textbooks. These exercises cover a range of topics from basic networking to advanced concepts such as software defined networking and network function virtualization. They include wired and wireless networking based exercises. GENI is also used as a platform for applications that enhance STEM education at the high-school level and as a platform for MOOC courses that use an interactive approach to teach Internet concepts to non-computer scientists.

Under a cloud of uncertainty: legal questions affecting internet storage and transmission of copyright-protected video content

The rapid growth of multimedia consumption has triggered technical, economic, and business innovations that improve the quality and accessibility of content. It has also opened new markets, promising large revenues for industry players. However, new technologies also pose new questions regarding the legal aspects of content delivery, which are often resolved through litigation between copyright owners and content distributors. The precedents set by these cases will act as a game changer in the content delivery industry, and will shape the existing offerings in the market in terms of how new technologies can be deployed and what kind of pricing strategies can be associated with them. In this article, we offer a tutorial on key copyright and communications laws and decisions related to storage and transmission of video content over the Internet. We summarize legal limitations on the deployment of new technologies and pricing mechanisms, and explain the implications of recent lawsuits. Understanding these concerns is essential for engineers engaged in designing the technical and economic aspects of video delivery systems.