Security issues and solutions in multicast content distribution: a survey

Multicast enables efficient large-scale content distribution by providing an efficient transport mechanism for one-to-many and many-to-many communication. The very properties that make multicast attractive, however, also make it a challenging environment in which to provide content security. We show how the fundamental properties of the multicast paradigm cause security issues and vulnerabilities. We focus on four areas of research in security for multicast content distribution: receiver access control, group key management, multicast source authentication, and multicast fingerprinting. For each we explain the vulnerabilities, discuss the objectives of solutions, and survey work in the area. Also, we briefly highlight other security issues in multicast content distribution including source access control, secure multicast routing, and group policy specification. We then outline several future research directions.     

Multicast server selection: problems, complexity, and solutions

We formulate and investigate fundamental problems that arise when multicast servers, that deliver content to multiple clients simultaneously, are replicated to enhance scalability and performance. Our study consists of two parts. First, we consider the problem under the assumption that the multicast clients are static for the duration of the multicast content distribution session. In this context, we examine two models for server behavior: fixed-rate servers, which transmit at a constant rate, and rate-adaptive servers, which adapt their transmission rate based on network conditions and/or feedback from clients. In both cases, we show that general versions of the client assignment problems are NP-hard. We then develop and evaluate efficient algorithms for interesting special cases, as well as heuristics for general cases. Second, we consider the case in which the set of clients changes dynamically during the multicast content distribution session. We again consider both fixed-rate and rate-adaptive servers. We formulate the problem as a Markov decision process, capturing the costs associated with trees, as well as the transition costs to dynamically change the trees. We use the properties of optimal solutions for small examples to develop a set of dynamic server selection heuristics.     

Comments on "Modeling TCP reno performance: a simple model and its empirical Validation"

In this Comments, several errors in Padhye , 2000, are pointed out. The more serious of these errors result in an over prediction of the send rate. The expression obtained for send rate in this Comments leads to greater accuracy when compared with the measurement data than the originals end rate expression in Padhye et al.     

Structural,optical and electrical properties of Zn-doped SnO2 nanoparticles synthesized by the co-precipitation technique

Nanometric size Zn-doped SnO₂ particles with Zn concentration varying from 1 to 6 % were prepared using the co-precipitation method. X-ray diffraction patterns show for all samples a typical rutile-type tetragonal structure of SnO₂ without any additional peaks from spurious phases. These results together with transmission electron microscopy analyses have shown that the size of the nanoparticles decreases with Zn doping down to 4 nm. According to UV–visible absorption measurements this decrease of particle size is accompanied by a decrease of the band gap value from 3.34 eV for SnO₂ down to 3.28 eV for 6 % Zn doping. The electrical conductivity of the system has been investigated between 473 and 718 K, in the 200 Hz–5 MHz frequency range, by means of impedance spectroscopy. The temperature dependence of the bulk conductivity was found to obey the Arrhenius law with activation energies of 0.74 eV for SnO₂ and 0.69 eV for 6 % Zn doping.     

AC actuation contribution to the induced electromotive force in the miniaturized inductive planar microphone

In this paper, we aim to analyze the gain ratio in the output induced voltage of a CMOS-compatible miniaturized electrodynamic microphone which is based on the use of two coplanar concentric inductors. These latter are comparable to a concentric transformer with a secondary situated on the microphone diaphragm top. The study has been applied when the outer inductor is actuated using an AC bias instead of DC leading to a time-variable B-field. The induced output voltage expression has been evaluated using two distinct analytic methods: the magnetic field derivation and the electric field approach. When an AC current with frequency above that of the acoustic band is used to bias the primary, results show that the induced voltage increases and becomes independent from the incident pressure wave frequency. The paper demonstrates also that with an AC bias, the microphone induced voltage values can reach the order of hundreds of µVs, as opposed to only few µVs when applying a DC bias. The gain in the induced voltage has been investigated and it is shown that it can be correlated to the AC current frequency, ω_c, and the inner inductor fluctuation frequency, ω_p. Moreover, this has been quantified analytically and it is shown that it equals ω_c/8ω_p. This result will not only enhance the overall performance of the microphone, but will also make the preamplification design less complicated by increasing the SNR ratio.     

Low communication cost (LCC) scheme for localizing mobile wireless sensor networks

In recent years, the number of applications utilizing mobile wireless sensor networks (WSNs) has increased, with the intent of localization for the purposes of monitoring and obtaining data from hazardous areas. Location of the event is very critical in WSN, as sensing data is almost meaningless without the location information. In this paper, two Monte Carlo based localization schemes termed MCL and MSL* are studied. MCL obtains its location through anchor nodes whereas MSL* uses both anchor nodes and normal nodes. The use of normal nodes would increase accuracy and reduce dependency on anchor nodes, but increases communication costs. For this reason, we introduce a new approach called low communication cost schemes to reduce communication cost. Unlike MSL* which chooses all normal nodes found in the neighbor, the proposed scheme uses set theory to only select intersected nodes. To evaluate our method, we simulate in our proposed scheme the use of the same MSL* settings and simulators. From the simulation, we find out that our proposed scheme is able to reduce communication cost—the number of messages sent—by a minimum of 0.02 and a maximum of 0.30 with an average of 0.18, for varying node densities from 6 to 20, while nonetheless able to retain similar MSL* accuracy rates.     

Robustness,Stability, and Gains of Utility Maximization Algorithms for Mobile Ad Hoc Networks

Cross-layer designs (CLDs) have the potential to better utilize network resources than a traditional layered protocol architecture, providing better communication services to end-users. This is particularly relevant in MANETs, which are characterized by a scarcity of network resources, in particular bandwidth. While many papers have demonstrated the potential performance benefit that CLDs can provide, their evaluation is often done under idealized scenarios, such as instantaneous message transmission times, complete topology knowledge, and/or zero message loss rates. Nodes in real MANETs do typically experience message losses, message delays, and have at best a partial and most likely inaccurate knowledge of the dynamic network topology. Our work focuses on realistic evaluations of a specific CLD approach. We propose a robust and stable version of a network utility maximization algorithm that optimizes the medium access probabilities at the MAC layer jointly with the end-to-end sessions rates at the transport layer. We report on stability tests with different link failure scenarios in case of synchronous and asynchronous message updates, convergence speed, and link utilizations. The results show that the algorithm converges even with a very high rate of link transmission failures and can tolerate asynchronous parameters updates. The CLD fully utilizes the link capacities and provides a network capacity gain of up to 250 %. The proposed modified CLD approach is therefore both beneficial and practical for real MANETs.