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

This book brings together the various paper publications by Kerner and his coauthors in a concise and readable manner.

Vehicular Traffic Flow Theory: Three, Not Two Phases [review of "Introduction to Modern Traffic Flow Theory and Control: The Long Road to Three-Phase Traffic Theory; Kerner, B.S.; 2009) ]

Ad hoc and sensor networks are making their way from research to real-world deployments. Body and personal-area networks, intelligent homes, environmental monitoring or inter-vehicle communications: there is almost nothing left that is not going to be smart and networked. While a great amount of research has been devoted to the pure networking aspects, ad hoc and sensor networks will not be successfully deployed if security, dependability, and privacy issues are not addressed adequately.

As the first book devoted to the topic, this volume constitutes the thoroughly refereed post-proceedings of the First European Workshop on Security in Ad-hoc and Sensor Networks, ESAS, 2004, held in Heidelberg, Germany in August 2004. The 17 revised full papers were carefully reviewed and selected from 55 submissions. Among the key topics addressed are key distribution and management, authentication, energy-aware cryptographic primitives, anonymity and pseudonymity, secure diffusion, secure peer-to-peer overlays, and RFIDs.

Security in Ad-hoc and Sensor Networks

Vehicular Dedicated Short Range Communication (DSRC) promises to reduce accidents by enabling assistance systems such as cross-traffic assistance. This application requires movement information from vehicles that are in Non-Line-Of-Sight (NLOS) due to buildings at intersection corners. DSRC is foreseen to use IEEE 802.11p to deliver regular Cooperative Awareness Messages (CAM). Due to the high operational frequency of 5.9GHz, the ability to provide reliable NLOS reception is often put into question.

We performed an extensive field test specifically targeted to measure DSRC NLOS reception quality. As a novelty, tested intersections were methodically selected to reflect typical urban intersections (in Munich) and the test setup was specifically designed to provide comparable and generalizable results. This allowed us to determine the influence of factors like building positions. The collected data shows that NLOS reception is possible. Reception rates stay mostly well above 50% for distances of 50 meters to intersection center with blocked LOS.

Real-world measurements of non-line-of-sight reception quality for 5.9GHz IEEE 802.11p at intersections

Address clustering tries to break the privacy of bitcoin users by linking all addresses created by an individual user, based on information available from the blockchain. As an alternative information source, observations of the underlying peer-to-peer network have also been used to attack the privacy of users. In this paper, we assess whether combining blockchain and network information may facilitate the clustering process. For this purpose, we apply all applicable clustering heuristics that are known to us to current blockchain information and associate the resulting clusters with IP address information extracted from observing the message flooding process of the bitcoin network. The results indicate that only a small share of clusters (less than 8%) were conspicuously associated with a single IP address. Also, only a small number of IP addresses showed a conspicuous association with a single cluster.

/pdf/could-network-information-facilitate-address-clustering-in-pwjva8a0ef.pdf

Could Network Information Facilitate Address Clustering in Bitcoin

Inter-vehicle communication promises to prevent accidents by enabling applications such as cross-traffic assistance. This application requires information from vehicles in Non-Line-of-Sight (NLOS) areas due to building at intersection corners. The periodic Cooperative Awareness Messages (CAM) are foreseen to be sent via 5.9 GHz IEEE 802.11p. While it is known that existing micro-cell models might not apply well, validated propagation models for vehicular 5.9 GHz NLOS conditions are still missing. In this paper, we develop a 5.9 GHz NLOS path-loss and fading model based on real-world measurements at a representative selection of intersections in the city of Munich. We show that a) the measurement data can very well be fitted to an analytical model, b) the model incorporates specific geometric aspects in closed-form as well as normally distributed fading in NLOS, and c) the model is of low complexity, thus, could be used in large-scale packet-level simulations. A comparison to existing micro-cell models shows that our model significantly differs.

Hannes Hartenstein

Papers

Vehicular Traffic Flow Theory: Three, Not Two Phases [review of "Introduction to Modern Traffic Flow Theory and Control: The Long Road to Three-Phase Traffic Theory; Kerner, B.S.; 2009) ]

Security in Ad-hoc and Sensor Networks

Real-world measurements of non-line-of-sight reception quality for 5.9GHz IEEE 802.11p at intersections

Could Network Information Facilitate Address Clustering in Bitcoin

A validated 5.9 GHz Non-Line-of-Sight path-loss and fading model for inter-vehicle communication