Vehicle position is one of the most valuable pieces of information in a Vehicular Adhoc NETwork (VANET). The main contribution of this work is a novel approach to enhancing position security in VANETs. We achieve local security by enlisting the help of on-board radar to detect neighboring vehicles and to confirm their announced coordinates. Local security is extended to achieve global security by using preset position-based groups to create a communication network and by using a dynamic challenging mechanism to confirm remote position information. Our solution is predicated on the widely accepted assumption that the vast majority of vehicles are honest and behave responsively. Extensive simulations confirm the quality of the proposed solution by measuring how fast compromised vehicles can be detected under various conditions.

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Although the Internet Archive's Wayback Machine is the largest and most well-known web archive, there have been a number of public web archives that have emerged in the last several years. With varying resources, audiences and collection development policies, these archives have varying levels of overlap with each other. While individual archives can be measured in terms of number of URIs, number of copies per URI, and intersection with other archives, to date there has been no answer to the question "How much of the Web is archived?" We study the question by approximating the Web using sample URIs from DMOZ, Delicious, Bitly, and search engine indexes; and, counting the number of copies of the sample URIs exist in various public web archives. Each sample set provides its own bias. The results from our sample sets indicate that range from 35%-90% of the Web has at least one archived copy, 17%-49% has between 2-5 copies, 1%-8% has 6-10 copies, and 8%-63% has more than 10 copies in public web archives. The number of URI copies varies as a function of time, but no more than 31.3% of URIs are archived more than once per month.

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Abstract-In this paper, we introduce DRIH-MAC, a distributed receiver-initiated medium access control protocol for communication among nanonodes in a wireless electromagnetic nanonetwork. DRIH-MAC is developed based on the following principles: 1) communication starts via the receiver with the goal of maximizing the energy utilization; 2) the distributed scheme for accessing the medium is designed based on graph coloring; and 3) communication scheduling works in coordination with the energy harvesting process. DRIH-MAC is based on a probabilistic scheme to create a scalable and light-weight solution, which minimizes collisions and maximizes the utilization of harvested energy, and can be used in a wide variety of applications. Through simulation experiments, we demonstrate the efficiency of DRIH-MAC in a sample medical monitoring application. In particular, DRIH-MAC can improve energy utilization by 50% as compared to a random MAC protocol. Furthermore, it can satisfy application requirements such as delay, even with low energy harvesting rates.

Abstract-We present a method for accurate aggregation of highway traffic information in vehicular ad hoc networks (VANETs). Highway congestion notification applications need to disseminate information about traffic conditions to distant vehicles. In dense traffic, aggregation is needed to allow a single frame to carry information about a large number of vehicles. Our technique, CASCADE (Clusterbased Accurate Syntactic Compression of Aggregated Data in VANETs), uses compression to provide aggregation without losing accuracy. As a part of CASCADE, we present probabilistic Inter-Vehicle Geocast, allowing the rebroadcasting of frames to depend upon the surrounding vehicle density. We show that the frame reception rate is improved with this modification. CASCADE provides each vehicle with data that is highly accurate, represents a large area in front of the vehicle, and can be combined with aggregated data from other vehicles to further extend the covered area.

-In this paper, we propose an algorithm for joint adaptation of transmission power and contention window to improve the performance of vehicular network in a cross layer approach. The high mobility of vehicles in vehicular communication results in the change in topology of the Vehicular Ad-hoc Network (VANET) dynamically, and the communication link between two vehicles might remain active only for short duration of time. In order for VANET to make a connection for long time and to mitigate adverse effects due to high and fixed transmission power, the proposed algorithm adapts transmission power dynamically based on estimated local traffic density. In addition to that, the prioritization of messages according to their urgency is performed for timely propagation of high priority messages to the destination region. In this paper, we incorporate the contention based MAC protocol 802.11e enhanced distributed channel access (EDCA) mechanism to implement a prioritybased vehicle-to-vehicle (V2V) communication. Simulation results show that the proposed algorithm is successful in getting better throughput with lower average end-to-end delay than the algorithm with static/default parameters.

We introduce NOTICE, a secure, privacy-aware architecture for the notification of traffic incidents. Using sensor belts embedded in the roadway, traffic-related messages and advisories are carried between belts by passing cars. NOTICE moves the responsibility for making decisions about trafficrelated information dissemination to the infrastructure rather than leaving those decisions with the vehicles, which may have incomplete or incorrect knowledge. Extensive simulation showed that NOTICE can provide "up-to-the-minute" notification of road incidents.