HTTP/2 supersedes HTTP/1.1 to tackle the performance challenges of the modern Web. A highly anticipated feature is Server Push, enabling servers to send data without explicit client requests, thus potentially saving time. Although guidelines on how to use Server Push emerged, measurements have shown that it can easily be used in a suboptimal way and hurt instead of improving performance. We thus tackle the question if the current Web can make better use of Server Push. First, we enable real-world websites to be replayed in a testbed to study the effects of different Server Push strategies. Using this, we next revisit proposed guidelines to grasp their performance impact. Finally, based on our results, we propose a novel strategy using an alternative server scheduler that enables to interleave resources. This improves the visual progress for some websites, with minor modifications to the deployment. Still, our results highlight the limits of Server Push: a deep understanding of web engineering is required to make optimal use of it, and not every site will benefit.

Pervasive applications evolve around the user's context, making it a full-fledged communication party. However, no equivalent approach to End-to-End communication exists that allows a sender to bind data, through encryption, to a target context. Existing solutions require central infrastructures or only apply to the immediate context, restricting pervasive applications. We propose Encryption to Trusted Contexts (ETC), a communication security building block that enforces context bindings while preserving the data handling and forwarding mechanisms of the original application. Our approach leverages a Broadcast Encryption scheme to protect data in transit and binds decryption to the verification of an expressive, flexible context specification based on trusted, unforgeable sensing. Data can then be encrypted from and to any context, securely exchanged among devices, and made accessible only within the specified context. We demonstrate the feasibility of ETC in a prototypical implementation for ARM TrustZone devices, realizing communication security for context-driven, pervasive applications.

Mobile offloading overcomes the resource limitations of offloader devices by splitting resource-intensive tasks and allocating subtasks to nearby offloadee devices. In processing its subtask, each offloadee effectively executes foreign and untrusted code which might both harm the device and exhaust its resources. Given the personal nature and constrained resources of offloadee devices, such as smartphones, precise control at the offloadee over the execution environment of offloaded tasks as well as the provided and consumed resources then is a natural requirement for the success of offloading approaches. We thus contribute a mechanism for fine-grained resource control of local task execution, benefitting allocation approaches by precisely assessing, advertising, and guaranteeing offloadee processing resources. Our design protects local device integrity and usability by isolating the execution of each task in a dedicated Linux container with precisely defined resource constraints. We highlight the performance and immediate applicability of our design through a prototypical implementation using LXC containers on COTS Android smartphones that achieves controllable task execution at minimal costs: Each container starts up in only 2 ms, imposes less than 5 % computation overhead, and consumes only 10MB of memory.

More and more Internet-enabled devices, such as server instances or smartphones, have multiple network interfaces. Multipath TCP (MPTCP) has proven to increase bandwidth for these devices, while remaining compatible with the existing network infrastructure and applications. For interactive applications and services, however, low latency and low jitter often is more important than bandwidth. In this paper, we rethink the MPTCP approach, focusing on end-to-end latency and jitter. We propose ReMP TCP, an MPTCP extension that sends data redundantly over multiple paths in the network. Exchanging bandwidth for latency, this approach guarantees the lowest possible latency in existing best-effort networks. The integration into the MPTCP protocol provides benefits such as transparent end-to-end connection establishment, multipath-enabled congestion control, and the prevention of head of line blocking. We discuss end-to-end latency in multipath environments considering both queuing delays and packet drops. Further, we evaluate the performance of our ReMP TCP Linux Kernel implementation for data center and mobile scenarios in Mininet and real world experiments. We show for a real world mobile scenario in a stressed environment that ReMP TCP can halve the average round-trip time and reduce its standard deviation by a factor of 19.

While users can ubiquitously access the Internet via their Wi-Fi network or their mobile carrier network, access to foreign private Wi-Fi networks is mostly prohibited. This is because private APs have no means of authenticating foreign mobile users prior to granting access to their network, entailing severe security and liability risks. However, such Wi-Fi roaming would make the vast network resources of private users available on a collaborative basis. We propose Collaborative On-demand Wi-Fi Sharing (COWS), offering 802.1×-equivalent authentication of foreign users at private APs without the need for elaborate, hierarchical authentication infrastructures. COWS embeds authentication credentials into 802.11 association requests, enabling APs to establish 802.11 AP networks exclusively on-demand and after an authentication of the mobile user at her home network provider. Our evaluation using Android smartphones and various authentication provider instances shows the real-life applicability of COWS, enabling lightweight, collaborative Wi-Fi roaming at the APs of private users.

Within the Internet of Things (IoT), Smart Things (STs) promise to permeate all contexts of daily life, offering digital access to their physical functionality. Mobile users then would be able to ubiquitously and spontaneously interact with things they encounter, enabling a wealth of diverse usage scenarios and applications. Currently, however, ST interaction requires a pre-controlled Internet or network connection as well as the prior installation of the ST-specific interaction interface, i.e., smartphone app. Users can thus only interact with known things, in contrast to the vision of spontaneous, ubiquitous discovery and interaction. We thus propose STIF (Smart Things Interaction Framework), enabling local wireless discovery of STs spontaneously via Wi-Fi, Bluetooth Low Energy, Visible Light Communication, or Acoustic Communication. STIF allows STs to transmit their interaction interface directly to users and supports interaction based on user input via touch and AR GUIs as well as motion and speech recognition. We implement STIF for Android phones as well as Arduino and Raspberry Pi things and demonstrate the real-life applicability of the supported communication and interaction techniques.

Mobile users are continuously surrounded by heterogeneous (mobile) devices that provide a basis for direct multimedia interaction within the immediate physical context. However, current multimedia approaches are restricted to sense the availability of devices and their respective multimedia application content through Internet services that manage the locality of devices and content. Each service thereby manages only the narrow context of each device according to the respective application, preventing devices and approaches from sensing the diversity, spontaneity, and dynamics of mobile contexts and the physical interaction scope.

The proliferation, flexibility, and mobility of wireless communication devices provides a readily available basis for ubiquitous mobile communication. However, the network-centric design of 802.11 does not support the spontaneity, continuity, and ubiquitous scope of mobile communication for two reasons: i) The time and maintenance overhead of 802.11 networks prevents spontaneous device interaction, and ii) 802.11 restricts the communication scope to devices in a common network. We thus enable ubiquitous wireless communication, independent from 802.11 network structures in CA-Fi, a continuous, low-overhead communication channel concurrent to 802.11 associations. CA-Fi augments 802.11 with an association-less broadcast mechanism of up to 30 kB/s, preserving up to 70 % of simultaneous 802.11 throughput and enabling unrestricted and instant networking in the wireless medium. Directly addressing applications in 802.11 frames using Bloom filters enables message aggregation for space efficiency and saves communication overhead by unifying peer and application discovery. CA-Fi inherently supports duty cycling and saves up to 44 % of the energy consumption of the 802.11 ad-hoc mode.