Yan Grunenberger

Breaking for commercials: characterizing mobile advertising

Mobile phones and tablets can be considered as the first incarnation of the post-PC era. Their explosive adoption rate has been driven by a number of factors, with the most signifcant influence being applications (apps) and app markets. Individuals and organizations are able to develop and publish apps, and the most popular form of monetization is mobile advertising. The mobile advertisement (ad) ecosystem has been the target of prior research, but these works typically focused on a small set of apps or are from a user privacy perspective. In this work we make use of a unique, anonymized data set corresponding to one day of traffic for a major European mobile carrier with more than 3 million subscribers. We further take a principled approach to characterize mobile ad traffic along a number of dimensions, such as overall traffic, frequency, as well as possible implications in terms of energy on a mobile device. Our analysis demonstrates a number of inefficiencies in todays ad delivery. We discuss the benefits of well-known techniques, such as pre-fetching and caching, to limit the energy and network signalling overhead caused by current systems. A prototype implementation on Android devices demonstrates an improvement of 50 % in terms of energy consumption for offline ad-sponsored apps while limiting the amount of ad related traffic.

The Cost of the "S" in HTTPS

Increased user concern over security and privacy on the Internet has led to widespread adoption of HTTPS, the secure version of HTTP. HTTPS authenticates the communicating end points and provides confidentiality for the ensuing communication. However, as with any security solution, it does not come for free. HTTPS may introduce overhead in terms of infrastructure costs, communication latency, data usage, and energy consumption. Moreover, given the opaqueness of the encrypted communication, any in-network value added services requiring visibility into application layer content, such as caches and virus scanners, become ineffective. This paper attempts to shed some light on these costs. First, taking advantage of datasets collected from large ISPs, we examine the accelerating adoption of HTTPS over the last three years. Second, we quantify the direct and indirect costs of this evolution. Our results show that, indeed, security does not come for free. This work thus aims to stimulate discussion on technologies that can mitigate the costs of HTTPS while still protecting the users privacy.

Experience with an implementation of the Idle Sense wireless access method

An overwhelming part of research work on wireless networks validates new concepts or protocols with simulation or analytical modeling. Unlike this approach, we present our experience with implementing the Idle Sense access method on programmable off-the-shelf hardware---the Intel IPW2915/abg chipset. We also present measurements and performance comparisons of Idle Sense with respect to the Intel implementation of the 802.11 DCF (Distributed Coordination Function) standard. Implementing a modified MAC protocol on constrained devices presents several challenges: difficulty of programming without support for multiplication, division, and floating point arithmetic, absence of support for debugging and high precision measurement. To achieve our objectives, we had to overcome the limitations of the hardware platform and solve several issues. In particular, we have implemented the adaptation algorithm with approximate values of control parameters without the division operation and taken advantage of some fields in data frames to trace the execution and test the implemented access method. Finally, we have measured its performance to confirm good properties of Idle Sense: it obtains slightly better throughput, much better fairness, and significantly lower collision rate compared to the Intel implementation of the 802.11 DCF standard.

An Asymmetric Access Point for Solving the Unfairness Problem in WLANs

In atypical deployment of IEEE 802.11 wireless LANs in the infrastructure mode, an access point acts as abridge between the wireless and the wired parts of the network. Under the current IEEE 802.11 Distributed Coordination Function (DCF) access method, which provides equal channel access probability to all devices in a cell, the access point cannot relay all the frames that it receives on the downlink. This causes significant unfairness between upload and download connections, long delays, and frame losses. This unfairness problem comes from the not-so-complex interaction of transport-layer protocols with the MAC-layer access method. The main problem is that the access point requires more transmission attempt probability than wireless stations for correct operation at the transport layer. In this paper, we propose to solve the unfairness problem in a simple elegant way at the MAC layer. We define the operation of an Asymmetric Access Point that benefits from a sufficient transmission capacity with respect to wireless stations so that the overall performance improves. The proposed method of operation is intrinsically adaptive so that when the access point does not need the increased capacity, it is used by wireless stations. We validate the proposed access method by simulation to compare it with other solutions based on IEEE 802.11e. Unlike many papers in this domain, which only validate MAC-layer modifications through simulation or analytical modeling, we provide measurement data gathered on an experimental prototype that uses wireless cards implementing the proposed method.

RILAnalyzer: a comprehensive 3G monitor on your phone

The popularity of smartphones, cloud computing, and the app store model have led to cellular networks being used in a completely different way than what they were designed for. As a consequence, mobile applications impose new challenges in the design and efficient configuration of constrained networks to maximize applications performance. Such difficulties are largely caused by the lack of cross-layer under- standing of interactions between different entities -applications, devices, the network and its management plane. In this paper, we describe RILAnalyzer, an open-source tool that provides mechanisms to perform network analysis from within a mobile device. RILAnalyzer is capable of recording low-level radio information and accurate cellular net- work control-plane data, as well as user-plane data. We demonstrate how such data can be used to identify previously overlooked issues. Through a small user study across four cellular network providers in two European countries we infer how different network configurations are in reality and explore how such configurations interact with application logic, causing network and energy overheads.

Virtual Access Points for Transparent Mobility in Wireless LANs

Mobility management in WiFi networks is still an open issue today: there is no standard method defined, and client station mobility is handled either via proprietary protocols, or simply by re- association. However, managing mobility in an infrastructure network is utterly important for several reasons: controlling delay and jitter in communications, managing clients from the network, optimizing performance. We propose the concept of virtual access points to manage mobile station in infrastructure networks. In this scheme, stations are not aware that they move, and all the complexity is pushed back inside the network. It is then possible to control mobility from a global point of vue, to optimize network resources for mobile stations, hence providing a better quality of service. Finally, this scheme is compatible with existing clients without any hardware nor software modification.

Experimenting With Commodity 802.11 Hardware: Overview and Future Directions

The huge adoption of 802.11 technologies has triggered a vast amount of experimentally-driven research works. These works range from performance analysis to protocol enhancements, including the proposal of novel applications and services. Due to the affordability of the technology, this experimental research is typically based on commercial off-the-shelf (COTS) devices, and, given the rate at which 802.11 releases new standards (which are adopted into new, affordable devices), the field is likely to continue to produce results. In this paper, we review and categorise the most prevalent works carried out with 802.11 COTS devices over the past 15 years, to present a timely snapshot of the areas that have attracted the most attention so far, through a taxonomy that distinguishes between performance studies, enhancements, services, and methodology. In this way, we provide a quick overview of the results achieved by the research community that enables prospective authors to identify potential areas of new research, some of which are discussed after the presentation of the survey.

When assistance becomes dependence: characterizing the costs and inefficiencies of A-GPS

Location based services are a vital component of the mobile ecosystem. Among all the location technologies used behind the scenes, A-GPS (Assisted-GPS) is considered to be the most accurate. Unlike standalone GPS systems, A-GPS uses network support to speed nup position fix. However, it can be a dangerous strategy due to varying cell conditions which may impair performance, sometimes potentially neglecting the expected benefits of the original design. We present the characterization of the accuracy, location acquisition speed, energy cost, and network dependency of the state of the art A-GPS receivers shipped in popular mobile devices. Our analysis is based on active measurements, an exhaustive on-device analysis, and cellular traffic traces processing. The results reveals a number of inefficiencies as a result of the strong dependence on the cellular network to obtain assisting data, implementation, and integration problems.

Prototyping with SDR: A quick way to play with next-gen communications systems

In this paper we present our approach regarding the implementation of new wireless radio receivers exploiting filterbank techniques, using a software-development driven approach. The fact that most of the common radio communication systems share a similar structure has been exploited to create a framework which provides a generic layout and tools to construct reconfigurable transmitters and/or receivers. By combining our own generic object-oriented framework built on top of the GNU Radio software framework with the use of the Universal Software Radio Peripheral version 2 (USRP2), we have been able to quickly implement a working proof of concept of an Uplink (UL) Filterbank Multicarrier (FBMC) receiver, both for Single-Input Single-Output (SISO) and Multiple-Input Multiple-Output (MIMO) scenario, within the 7th European framework project called PHYDYAS. As well, a description of the methodology we have applied from software engineering in order to build this demonstrator is herein included, which shows the suitability of using Software Defined Radio (SDR) technologies for fast prototyping of new wireless communication systems.

Power-boosting residential wired broadband

Residential users often face performance issues while using wired broadband connection with bandwidth hungry applications such as high-quality video streaming. Despite residential users have both wired (ADSL, cable, fibre) and wireless (3G, 4G) access technology at disposal, there are no applications capable of exploiting all the available capacity across different access technologies. In this demo we present an over the top (OTT) system, able to strategically On-Load a fraction of the data traffic from the wired to the cellular network, providing a power-boost for video streaming application over HTTP. We show that our solution is effective in reducing both pre-fetching and download time.