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 memo defines a portion of the Management Information Base (MIB) for use with network management protocols in the Internet community. In particular, it describes a set of managed objects that allow monitoring of running instances of RObust Header Compression (ROHC). The managed objects defined in this memo are grouped into three MIB modules. The ROHC-MIB module defines managed objects shared by all ROHC profiles, the ROHC-UNCOMPRESSED-MIB module defines managed objects specific to the ROHC uncompressed profile, the ROHC-RTP-MIB module defines managed objects specific to the ROHC RTP (Real-Time Transport Protocol) profile, the ROHC UDP (User Datagram Protocol) profile, the ROHC ESP (Encapsulating Security Payload) profile, and the ROHC LLA (Link Layer Assisted) profile. Quittek, et al. Standards Track [Page 1] RFC 3816 ROHC MIB June 2004

Definitions of Managed Objects for RObust Header Compression (ROHC)

We performed a simulative evaluation of Hierarchical MIPv6 in comparison with standard MIPv6 using the network simulator ns-2 for a ‘hot spot deployment’ scenario. The simulation scenario comprises four access routers and up to 50 mobile nodes that move randomly and communicate in accordance with the IEEE 802.11 wireless LAN standard. The study provides quantitative results of the improvements provided by HMIPv6 with respect to handoff latency, packet loss, signaling load and bandwidth per station. The simulation environment allowed us also to investigate the behavior of the protocol in extreme cases, e.g., under channel saturation conditions, and considering different traffic sources: CBR, Video, VoIP and TCP.

A simulation study on the performance of hierarchical mobile IPv6

In this letter we investigate near-lossless signal coding for which the reconstruction signal is required to have an absolute error in each component bounded by a tolerance /spl tau/. For differential coding no practical algorithm is known that computes an optimal reconstruction, i.e., one for which the sequence of consecutive differences has minimal entropy. In this letter we give the optimal lower bound for the entropy of the differences of the reconstruction and, in addition, present tighter bounds for some special cases.

On entropy minimization for near-lossless differential coding

The purpose of Virtual Traffic Light (VTL) applications is to increase traffic efficiency without the use of conventional traffic light infrastructure. With VTL applications, vehicles self-organize for intersection crossing based on wireless communication. Although VTL applications must comply with high safety requirements, no verification of VTL's safety has been provided so far. We present a VTL protocol that is verified to be fail-safe using model checking as a verification approach. Performance evaluation through simulation showed that the verified fail-safe VTL protocol delivers-although far from optimum-decent results with respect to such traffic efficiency metrics like throughput and travel time. The investigated efficiency optimization substantially improved efficiency, yet compromised the safety of VTL. We quantify the tradeoff between efficiency and safety and show that increasing the safety level deteriorates efficiency only marginally. In particular, a safety level increase by a factor of 1,000 increases travel time by approximately 2% in the studied scenario. Therefore, high safety requirements can be met while maintaining high efficiency gains.

Verification and evaluation of fail-safe Virtual Traffic Light applications

This special issue focuses on the technologies, applications,and services that support intelligent vehicle and transportation systems.

http://publications.lib.chalmers.se/records/fulltext/local_151663.pdf

Hannes Hartenstein

Papers

Definitions of Managed Objects for RObust Header Compression (ROHC)

A simulation study on the performance of hierarchical mobile IPv6

On entropy minimization for near-lossless differential coding

Verification and evaluation of fail-safe Virtual Traffic Light applications

Vehicular Communications [Scanning the Issue]