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 user's privacy.

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.

Content caching is a fundamental building block of the Internet. Caches are widely deployed at network edges to improve performance for end-users, and to reduce load on web servers and the backbone network. Considering mobile 3G/4G networks, however, the bottleneck is at the access link, where bandwidth is shared among all mobile terminals. As such, per-user capacity cannot grow to cope with the traffic demand. Unfortunately, caching policies would not reduce the load on the wireless link which would have to carry multiple copies of the same object that is being downloaded by multiple mobile terminals sharing the same access link.In this paper we investigate if it is worth to push the caching paradigm even farther. We hypothesize a system in which mobile terminals implement a local cache, where popular content can be pushed/pre-staged. This exploits the peculiar broadcast capability of the wireless channels to replicate content "for free" on all terminals, saving the cost of transmitting multiple copies of those popular objects. Relying on a large data set collected from a European mobile carrier, we analyse the content popularity characteristics of mobile traffic, and quantify the benefit that the push-tomobile system would produce. We found that content prestaging, by proactively and periodically broadcasting "bundles" of popular objects to devices, allows to both greatly i) improve users' performance and ii) reduce up to 20% (40%) the downloaded volume (number of requests) in optimistic scenarios with a bundle of 100 MB. However, some technical constraints and content characteristics could question the actual gain such system would reach in practice.

very selective A+International audienceIn a typical deployment of IEEE 802.11 wireless LANs in the infrastructure mode, an access point acts as a bridge between the wireless and the wired part of the network. Under the current IEEE 802.11 DCF access method, which provides equal channel access probability to all devices in a cell, the access point cannot relay all the frames it receives on the downlink. This causes significant unfairness between uplink and downlink flows, long delays, and frame losses. 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 and 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. Moreover, we provide measurement data gathered on an experimental prototype that uses wireless cards implementing the proposed method

Mobile phones in the 3G/4G era enable us to stay connected not only to the voice network, but also to online services like social networks. In this paper, we study the energy and network costs of mobile applications that provide continuous online presence (e.g. WhatsApp, Facebook, Skype). By combining measurements taken on the mobile and the cellular access network, we reveal a detailed picture of the mechanisms selected to implement online presence, along with their effect on handset energy consumption and network signaling traffic. We are surprised to find that simply having idle online presence apps on a mobile (that maintain connectivity in the background, with no user interaction) can drain the handset battery nine times more quickly. This high cost is partly due to online presence apps that are excessively "chatty", in particular when their design philosophy stems from a similar desktop version. However, we also find that the cost of background app traffic is disproportionately large because of cross-layer interactions in which the traffic unintentionally triggers the promotion of cellular network states. Our experiments show that both of these effects can be overcome with careful implementation. We posit that a two-way push notification system, with messages being sent at a low (regular) frequency and low volume by a networkaware sender, can alleviate many of the costs.

Given the urgency of standardizing the 5 th generation mobile systems (5G) to meet the ever more stringent demands of new applications, the importance of field trials and experimentation cannot be overstated. Practical experimentation with cellular networks has been historically reserved exclusively to operators, primarily due to equipment costs and licensing constraints. The state of play is changing with the advent of open-source cellular stacks based on increasingly more affordable software defined radio (SDR) systems. Comprehensive understanding of the performance, limitations, and interoperability of these tools however lacks. In this article we fill this gap, by assessing by means of controlled experiments the performance of today's most popular open software Evolved Node B (eNB) solutions in combination with different commodity User Equipment (UE) and an SDR alternative, over a range of practical settings. Although these cannot underpin complete 5G systems yet, their development is progressing rapidly and researchers have employed them for 5G specific applications including LTE unlicensed and network slicing. We further shed light onto the perils of open tools and give configuration guidelines that can be used to deploy these solutions effectively. Our results quantify the throughput attainable with each stack, their resource consumption footprint, and their reliability and bootstrap times in view of automating experimentation. Lastly, we evaluate qualitatively the extensibility of the solutions considered.

International audienceMobility 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

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 fifteen years, to present a timely snapshot of the areas that have attracted to most attention so far, though 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.