Torsten Zimmermann

ReMP TCP: Low latency multipath TCP

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.

Analyzing Metropolitan-Area Networking within Public Transportation Systems for Smart City Applications

In the scope of smart cities, mobile participatory sensing and metropolitan area networking on top of public transportation systems for communication offers widespread dissemination of information in both time and spatial domains. Specifically, the transportation network naturally reflects urban human mobility patterns between places of interest and interconnects hotspots where information is created and consumed by city- wide applications. Previous work has targeted communication exclusively between users of the public transportation system. In this paper, we provide an analysis of metropolitan networking within the transportation system itself. Instead of relying on user-generated contact traces purely between mobile entities, i.e., busses, we build on a comprehensive data set that contains the schedules and location data of busses as well as the location of infrastructure elements, such as bus stops. Our analysis shows the general feasibility of such a network as well as the, previously not considered, impact of infrastructure elements for information dissemination. The latter motivates delay-tolerant and location- driven communication, as well as participatory sensing using the transport system as a communication infrastructure.

Enabling ubiquitous interaction with smart things

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.

STEAN: A storage and transformation engine for advanced networking context

Legacy Internet systems and protocols are mostly static and keep state information in silo-style storage, thus making state migration, transformation and re-use difficult. Software Defined Networking (SDN) approaches in unison with Network Functions Virtualization (NFV) allow for more flexibility, yet they are currently restricted to a limited set of state migration options. Impeding the sharing of networking and system state severely limits the ability to optimally manage resources and dynamically adapt to a desirable overall configuration. We propose a generalized way to collect, store, transform, and share context between NFs in both the legacy Internet and NFV/SDN-driven systems. To this end, we design and implement a Storage and Transformation Engine for Advanced Networking Context (STEAN), which constitutes a shared context storage, making network state information available to other systems and protocols. Its pivotal feature is the ability to allow for state transformation as well as for persisting state to enable future reuse. By means of experimentation, we show that STEAN covers a diverse set of challenging use cases in legacy systems as well as in NFV/SDN-enabled systems.

Distributed Configuration, Authorization and Management in the Cloud-Based Internet of Things

Network-based deployments within the Internet of Things increasingly rely on the cloud-controlled federation of individual networks to configure, authorize, and manage devices across network borders. While this approach allows the convenient and reliable interconnection of networks, it raises severe security and safety concerns. These concerns range from a curious cloud provider accessing confidential data to a malicious cloud provider being able to physically control safety-critical devices. To overcome these concerns, we present D-CAM, which enables secure and distributed configuration, authorization, and management across network borders in the cloud-based Internet of Things. With D-CAM, we constrain the cloud to act as highly available and scalable storage for control messages. Consequently, we achieve reliable network control across network borders and strong security guarantees. Our evaluation confirms that D-CAM adds only a modest overhead and can scale to large networks.

A QoE Perspective on HTTP/2 Server Push

HTTP/2 was recently standardized to optimize the Web by promising faster Page Load Times (PLT) as compared to the widely deployed HTTP/1.1. One promising feature is HTTP/2 server push, which turns the former pull-only into a push-enabled Web. By enabling servers to preemptively push resources to the clients without explicit request, it promises further improvements of the overall PLT. Despite this potential, it remains unknown if server push can indeed yield human perceivable improvements. In this paper, we address this open question by assessing server push in both i) a laboratory and ii) a crowdsourcing study. Our study assesses the question if server push can lead to perceivable faster PLTs as compared to HTTP/1.1 and HTTP/2 without push. We base this study on a set of 28 push-enabled real-word websites selected in an Internet-wide measurement. Our results reveal that our subjects are able to perceive utilization of server push. However, its usage does not necessarily accomplish perceived PLT improvements and can sometimes even be noticeably detrimental.

Digging into Browser-based Crypto Mining.

Mining is the foundation of blockchain-based cryptocurrencies such as Bitcoin rewarding the miner for finding blocks for new transactions. The Monero currency enables mining with standard hardware in contrast to special hardware (ASICs) as often used in Bitcoin, paving the way for in-browser mining as a new revenue model for website operators. In this work, we study the prevalence of this new phenomenon. We identify and classify mining websites in 138M domains and present a new fingerprinting method which finds up to a factor of 5.7 more miners than publicly available block lists. Our work identifies and dissects Coinhive as the major browser-mining stakeholder. Further, we present a new method to associate mined blocks in the Monero blockchain to mining pools and uncover that Coinhive currently contributes 1.18% of mined blocks having turned over 1293 Moneros in June 2018.

A wireless application overlay for ubiquitous mobile multimedia sensing and interaction

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. Orthogonally, we facilitate direct and ubiquitous mobile multimedia sensing and interaction in 802.11 and 802.15.4 within the unrestricted physical context of mobile devices. Removing the need for Internet services or wireless networks, we derive a wireless service overlay over the sensed media in the locality of a device that exposes media to applications. Our technical evaluation shows the feasibility of the underlying uncoordinated, unrestricted network-less communication. We substantiate our design along an implementation of traditional and novel mobile use cases, illustrating the design space made accessible by our approach.

Characterizing a Meta-CDN

CDNs have reshaped the Internet architecture at large. They operate (globally) distributed networks of servers to reduce latencies as well as to increase availability for content and to handle large traffic bursts. Traditionally, content providers were mostly limited to a single CDN operator. However, in recent years, more and more content providers employ multiple CDNs to serve the same content and provide the same services. Thus, switching between CDNs, which can be beneficial to reduce costs or to select CDNs by optimal performance in different geographic regions or to overcome CDN-specific outages, becomes an important task. Services that tackle this task emerged, also known as CDN broker, Multi-CDN selectors, or Meta-CDNs. Despite their existence, little is known about Meta-CDN operation in the wild. In this paper, we thus shed light on this topic by dissecting a major Meta-CDN. Our analysis provides insights into its infrastructure, its operation in practice, and its usage by Internet sites. We leverage PlanetLab and Ripe Atlas as distributed infrastructures to study how a Meta-CDN impacts the web latency.

Is the Web ready for HTTP/2 Server Push?

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.