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.

Random graphs

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.

/pdf/spray-and-wait-an-efficient-routing-scheme-for-50seq3wqos.pdf

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

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.

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

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.

PORs: Proofs of Retrievability for Large Files

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.

/pdf/securing-vehicular-ad-hoc-networks-4sgegi8hgk.pdf

Securing vehicular ad hoc networks

We uncover the extend-only directed posets (EDP) structure as unification of recently discussed DAG-based Byzantine-tolerant conflict-free replicated data types (CRDT). We also derive an EDP-based key-value map, and give an outlook on an EDP-based systemic access control CRDT as formalization of the CRDT used in the Matrix messaging system.

/pdf/on-extend-only-directed-posets-and-derived-byzantine-1vmh73zw.pdf

On Extend-Only Directed Posets and Derived Byzantine-Tolerant Replicated Data Types

In a global sensor network different sensor platforms will be deployed. A 
grave obstacle on the way of building sensor networks out of different sensor nodes are incompatible implementations of network protocol stacks used with different sensor node platforms. We describe our efforts to overcome this obstacle in a heterogeneous sensor network consisting out of MICAz Motes and Sun SPOTs, both using an IEEE 802.15.4 radio chip. We explain the major differences in the respective network stacks and our approach to bridge them. A network stack that bridges the gap between different platforms allows for more flexible and robust networks.

/pdf/overcoming-a-communication-barrier-on-the-way-towards-a-1u885bctkp.pdf

Overcoming a Communication Barrier on the Way Towards a Global Sensor Network

IEEE Vehicular Technology Magazine: Foreword (Editorial)

Die effiziente Verwaltung und Bereitstellung von Identitätsdaten in heterogenen Systemumgebungen ist nach wie vor eine intensiv diskutierte Thematik. Verschärft wird die Diskussion durch den Einsatz von IuK-Diensten die institutionsübergreifend agieren und somit eine institutionsübergreifende Authentisierung und Autorisierung benötigen. Bisherige Umsetzungen im fakultativen, d.h. lokalen Kontext der ATIS (Abteilung Technische Infrastruktur), als Betreiber der Dienste für die Fakultät für Informatik, und Arbeiten im KIMProjekt (Karlsruher Integriertes InformationsManagement, [KIM]) haben ergeben, dass man diesbezüglich drei evolutionäre Phasen im lokalen Kontext eines einzelnen Betreibers und zwei in Bezug auf den universitätsweiten Kontext identifizieren kann. Diese Phasen werden vorgestellt und die Motivation für diese Phasen diskutiert.

/pdf/integriertes-management-von-identitaten-im-fakultativen-und-4bxzfzzdem.pdf

Integriertes Management von Identitäten im fakultativen und universitätsweiten Kontext

In fractal compression a signal is encoded by the parameters of a contractive transformation whose fix ed point (attractor) is an approximation of the original data. Thus fractal coding can be viewed as the optimization problem of finding in a set of admissible contractive transformations the transformation whose attractor is closest to a given signal. The standard fractal coding scheme based on the Collage Theorem produces only a suboptimal solution. We demonstrate by a reduction from MAXCUT that the problem of determining the optimal fractal code is NP-hard. To our knowledge, this is the first analysis of the intrinsic complexity of fractal coding. Additionally, we show that standard fractal coding is not an approximating algorithm for this problem.

Hannes Hartenstein

Papers

On Extend-Only Directed Posets and Derived Byzantine-Tolerant Replicated Data Types

Overcoming a Communication Barrier on the Way Towards a Global Sensor Network

IEEE Vehicular Technology Magazine: Foreword (Editorial)

Integriertes Management von Identitäten im fakultativen und universitätsweiten Kontext

Optimal Fractal Coding is NP-Hard 1 (Extended Abstract)