Hannes Hartenstein

Bio: Hannes Hartenstein is an academic researcher from Karlsruhe Institute of Technology. The author has contributed to research in topics: Vehicular ad hoc network & Wireless ad hoc network. The author has an hindex of 55, co-authored 234 publications receiving 14515 citations. Previous affiliations of Hannes Hartenstein include University of Mannheim & University of Freiburg.

Ensuring reproducibility through tool-based simulation process management

Abstract: For credibility of simulation results, reproducibility of simulation runs is a must. However, reproducibility requires a thorough management of all data involved in the simulation process. The corresponding management of data can be error-prone and time consuming if performed manually. In this paper we introduce a simulation management approach that ensures reproducibility and traceability of simulation runs as well as improves efficiency of simulation processes by automation of common simulation tasks. We implemented our approach as an Eclipse plugin. We show that information gained by explicit simulation management can be used to automatically organize and archive all necessary data to reproduce a simulation. While our tool was implemented with focus on the network simulator ns-2, our concepts can be applied to other simulation environments, too.

Model-Based Concurrency Analysis of Network Simulations

Abstract: To achieve highest performance, parallel simulation of networks on modern hardware architectures depends on large numbers of independent computational tasks However, the properties determining a network model's concurrency are still not well understood In this paper, we propose an analytical model that enables concurrency estimations based on model knowledge and on statistics gathered from sequential simulation runs In contrast to an automated concurrency analysis of event traces, the analytical approach enables insights into the relationship between the topology and communication patterns of the simulated network, and the resulting concurrency We consider three fundamentally different network models as implemented in the network simulators PeerSim and ns-3: a large-scale application-layer peer-to-peer network, IP-based routing in a fixed topology, and a wireless ad-hoc network For each model, we conduct an in-depth analysis, exposing the relationships between model characteristics and concurrency Our analysis is validated by comparing estimated concurrency values to reference results of a trace-based analysis The identification of key factors for concurrency forms a step towards a classification of network models according to their potential for parallelization

Analysis of trellis quantization for near-lossless image coding

Abstract: Summary form only given. We discuss several variations to the original algorithm proposed by Ke and Marcellin (see Proc. IEEE ICIP, Washington DC, 1995). We have extended the trellis quantization (TQ) scheme by performing two-row joint optmizations instead of optimizing row by row. Unfortunately, while increasing the computation time quite a bit, this has lead only to marginal coding gains. A progressive probability update scheme has lead to much better convergence and to a 0.3 bpp gain over the original fixed scheme. When using lossy plus near-lossless coding the lossy version can be used for better context modelling without increasing the computational complexity of the near-lossless residual coding. Improvements of 0.1-0.2 bpp were observed. Since it is computationally infeasible to include more pixels to be determined by the TQ process, one has the choice of either using better prediction/context-modelling or doing TQ. Our tests indicate that the preference should be given to sophisticated prediction/modelling.

Index Optimization for L-Diversified Database-as-a-Service.

Abstract: Preserving the anonymity of individuals by technical means when outsourcing databases to semi-trusted providers gained importance in recent years. Anonymization approaches exist that fulfill anonymity notions like \(\ell \)-diversity and can be used to outsource databases. However, indexes on anonymized data significantly differ from plaintext indexes both in terms of usage and possible performance gains. In most cases, it is not clear whether using an anonymized index is beneficial or not.

Random graphs

Abstract: We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

Spray and wait: an efficient routing scheme for intermittently connected mobile networks

Abstract: Intermittently connected mobile networks are sparse wireless networks where most of the time there does not exist a complete path from the source to the destination. These networks fall into the general category of Delay Tolerant Networks. There are many real networks that follow this paradigm, for example, wildlife tracking sensor networks, military networks, inter-planetary networks, etc. In this context, conventional routing schemes would fail.To deal with such networks researchers have suggested to use flooding-based routing schemes. While flooding-based schemes have a high probability of delivery, they waste a lot of energy and suffer from severe contention, which can significantly degrade their performance. Furthermore, proposed efforts to significantly reduce the overhead of flooding-based schemes have often be plagued by large delays. With this in mind, we introduce a new routing scheme, called Spray and Wait, that "sprays" a number of copies into the network, and then "waits" till one of these nodes meets the destination.Using theory and simulations we show that Spray and Wait outperforms all existing schemes with respect to both average message delivery delay and number of transmissions per message delivered; its overall performance is close to the optimal scheme. Furthermore, it is highly scalable retaining good performance under a large range of scenarios, unlike other schemes. Finally, it is simple to implement and to optimize in order to achieve given performance goals in practice.

Dedicated Short-Range Communications (DSRC) Standards in the United States

Abstract: Wireless vehicular communication has the potential to enable a host of new applications, the most important of which are a class of safety applications that can prevent collisions and save thousands of lives. The automotive industry is working to develop the dedicated short-range communication (DSRC) technology, for use in vehicle-to-vehicle and vehicle-to-roadside communication. The effectiveness of this technology is highly dependent on cooperative standards for interoperability. This paper explains the content and status of the DSRC standards being developed for deployment in the United States. Included in the discussion are the IEEE 802.11p amendment for wireless access in vehicular environments (WAVE), the IEEE 1609.2, 1609.3, and 1609.4 standards for Security, Network Services and Multi-Channel Operation, the SAE J2735 Message Set Dictionary, and the emerging SAE J2945.1 Communication Minimum Performance Requirements standard. The paper shows how these standards fit together to provide a comprehensive solution for DSRC. Most of the key standards are either recently published or expected to be completed in the coming year. A reader will gain a thorough understanding of DSRC technology for vehicular communication, including insights into why specific technical solutions are being adopted, and key challenges remaining for successful DSRC deployment. The U.S. Department of Transportation is planning to decide in 2013 whether to require DSRC equipment in new vehicles.

PORs: Proofs of Retrievability for Large Files

Abstract: In this paper, we define and explore proofs of retrievability (PORs). A POR scheme enables an archive or back-up service (prover) to produce a concise proof that a user (verifier) can retrieve a target file F, that is, that the archive retains and reliably transmits file data sufficient for the user to recover F in its entirety.A POR may be viewed as a kind of cryptographic proof of knowledge (POK), but one specially designed to handle a large file (or bitstring) F. We explore POR protocols here in which the communication costs, number of memory accesses for the prover, and storage requirements of the user (verifier) are small parameters essentially independent of the length of F. In addition to proposing new, practical POR constructions, we explore implementation considerations and optimizations that bear on previously explored, related schemes.In a POR, unlike a POK, neither the prover nor the verifier need actually have knowledge of F. PORs give rise to a new and unusual security definition whose formulation is another contribution of our work.We view PORs as an important tool for semi-trusted online archives. Existing cryptographic techniques help users ensure the privacy and integrity of files they retrieve. It is also natural, however, for users to want to verify that archives do not delete or modify files prior to retrieval. The goal of a POR is to accomplish these checks without users having to download the files themselves. A POR can also provide quality-of-service guarantees, i.e., show that a file is retrievable within a certain time bound.

Securing vehicular ad hoc networks

Abstract: Vehicular networks are very likely to be deployed in the coming years and thus become the most relevant form of mobile ad hoc networks. In this paper, we address the security of these networks. We provide a detailed threat analysis and devise an appropriate security architecture. We also describe some major design decisions still to be made, which in some cases have more than mere technical implications. We provide a set of security protocols, we show that they protect privacy and we analyze their robustness and efficiency.