This paper analyses how data dissemination occurs in mobile Opportunistic Networks by evaluating the impact of different parameters such as density of neighbors, communication range, and speed. There exist several analytical models to evaluate the data dissemination time in OppNets. These models were developed based on a very strong assumption of uniform distribution of infected nodes. We prove that this assumption does not work for the whole spectrum of mobile OppNets. This paper shows our simulation results validated with our analytical model and discusses the impact of different parameters on data dissemination.

This paper focuses on modeling the charateristics of opportunistic networks (OppNets). The motivation of this work is to develop a model which is closer to the reality to represent the data dissemination in OppNets. This paper shows our preliminary results validating our model in OppNets scenarios which give an opportunity to exchange data among a group of people.

Network Virtualization is claimed to be a key component of the Future Internet, providing the dynamic support of different networks with different paradigms and mechanisms in the same physical infrastructure. A major challenge in the dynamic provision of virtual networks is the efficient embedding of virtual resources into physical ones. Since this problem is known to be NP-hard, previous research focused on designing heuristic-based algorithms; most of them either do not consider a simultaneous embedding of virtual nodes and virtual links, or apply link-path formulation, leading to non-optimal solutions. This paper proposes an integer linear programming (ILP) formulation to solve the online virtual network embedding problem as a result of an objective function striving for the minimization of resource consumption and load balancing. To this end 3 different objective functions are proposed and evaluated. This approach applies multi-commodity flow constraint to accomplish a node-link formulation that optimizes the allocation of physical network resources. This proposal is evaluated against state of the art heuristics. The performance of the heuristics related to Virtual Network (VN) request acceptance ratio is, at least, 30% below the one of the Virtual Network Embedding Node-Link Formulation (VNE-NLF) method. From the three cost functions evaluated, the Weighted Shortest Distance Path (WSDP) is the one which embeds more VNs and also requires, on average, less physical resources per embedding.

Many airlines envision the deployment of wireless LAN infrastructure for video streaming to inflight entertainment devices attached to cabin seats. The sheer advantage of wireless LAN infrastructure is that it facilitates flexible configuration of cabin seat layout with less effort and low cost. The emerging IEEE 802.11n technology which has high throughput is an interesting option for such wireless LAN infrastructure. This paper evaluates the performance of video streaming over IEEE 802.11n, considering the QoS requirements of inflight video, by ns-2 simulation.

In this paper, we present a novel distributed algorithm to solve the logical topology reconfiguration problem for IP over WDM networks under dynamic traffic. From the optimization model proposed in, we apply the Lagrangian relaxation to eliminate the capacity constraint and form a dual problem whose optimal solution is the lower bound of the original one. The dual problem is then decomposed into subproblems, which can be solved in a distributed manner. Based on the solution of the dual problem, a heuristic algorithm is proposed to obtain a good feasible solution for the original reconfiguration problem. Our distributed algorithm fulfils all requirements of the reconfiguration process, such as no service disruption, load balancing in the new logical topology while allowing to add and to delete multiple lightpaths. Moreover, the distributed approach offers a high scalability. Not limited to small or medium-sized networks as the centralized model in, this distributed algorithm can be applied to large networks with the computation time increasing linearly with the network size. The performance of the proposed distributed algorithm, which lends itself to a protocol implementation, is investigated and compared with the corresponding centralized approach.

In WDM all-optical networks, the use of wavelength converters can increase the wavelength resource efficiency and reduce the blocking probability. However, all-optical wavelength converters are likely to remain costly devices. Moreover, the blocking probability does not decrease linearly with the number of converters. Hence, it is desirable that just a limited amount of wavelength converters are used in the whole network. In this case, a vital question arises: how many converters are enough and where to place these converters? In this paper, we introduce for the first time an exact ILP formulation to minimize the number of necessary wavelength converters as well as to place these converters in the network for a static traffic pattern, when its Routing Wavelength Assignment (RWA) is infeasible if no wavelength converter is used but feasible if the wavelength continuity constraint is relaxed. By running the optimization for numerous different random traffic patterns, we can at the end find the nodes with highest probability to place wavelength converters.

In this paper, we present a new approach to solve the logical topology reconfiguration problem for IP over WDM networks under dynamic traffic. Based on the measurement of lightpaths’ load, a change in the logical topology is made if some lightpath is highly loaded or under utilized. The change can be adding/deleting several lightpaths or just rerouting traffic in the current logical topology. The key idea of our approach is to determine a new logical topology so that the maximum lightpaths’ load at the time of reconfiguration is limited by a load-balance indicator, which is pre-defined as a system’s parameter. It ensures the network performance (in terms of lightpath utilization) and also increases the lifetime of the logical topology under dynamic traffic changes. Moreover, our approach ensures no network disruption during the reconfiguration process while allowing adding or deleting multiple lightpaths at the same time. The algorithm is formulated as a mixed integer linear programming (MILP). The performance is investigated and compared with Gencata’s approach through an illustrative numerical example. Because the proposed MILP is complex and can be applied only to small networks, an approximate model is also presented to solve the problem for some real-size networks.

Many distributed real-time embedded systems often perform critical functions, which implicitly require high reliability. Consequently, the application designer for a distributed real-time embedded system is confronted with a challenge of deriving a reliable schedule for a real-time application in the presence of individual component and common cause failures of the system. This paper proposes a formal framework for reliable scheduling of a real-time application over a distributed realtime embedded system considering both failures. The framework derives an optimal reliable schedule for the real-time application, while not violating the constraints of the application and the system resources.

In order to be able to simulate wireless networks in a non-uniform environment resulting in specific user distributions, it is essential to predict and control the stationary user distribution of the employed mobility model. We propose a framework to calculate turning probabilities at intersections of a graph-based mobility model to realize an arbitrary stationary user distribution on a street network. In this way, the user distribution can be fitted to a measured distribution. Our framework is able to cope with different average velocities on streets as well as different pausing probabilities at intersections. We evaluate its scope with the help of an example distribution on a European city center map featuring different street types and a variety of different crossings.

In a networked embedded system a real-time application is distributed and scheduled over a set of nodes, which are connected by means of heterogeneous networks. The application designer for such a system is often confronted with the challenge of providing better response time and low failure probability for the distributed application. These objectives are conflicting with each other hence some trade-off between these two design objectives is needed to ensure a satisfactory application schedule. More often the designer's satisfaction can be expressed as a set of aspiration bounds on the design objectives, that if attained will be a good schedule. This paper proposes a satisfying multiobjective mixed integer programming (MOMIP) framework for deriving such a schedule

Bandwidth trading schemes give peers an incentive to provide upload bandwidth to other peers in a P2P network for fast file distribution. A popular example is the tit-for-tat strategy used in the BitTorrent protocol. Although this game theoretical scheme provides an incentive to peers to contribute resources to the network it does not prevent unfairness and the performances of peers vary considerably. Therefore, we propose two new trading schemes, which are based on pricing. One uses explicit price information whereas the other scheme uses the download rates from other peers as the price. For both distributed algorithms the stable point provides a fair resource allocation as well as a Nash equilibrium, i.e. fairness is preserved although peers behave selfishly and try to maximise their own download rates only. We compare both pricing schemes with BitTorrent in simulations of static and dynamic networks. The pricing algorithms outperform BitTorrent with respect to fairness. With explicit prices the download rates converge faster to the fair equilibrium than with implicit ones

In this study we evaluate the ability of isolated wireless LAN access points to serve fast moving mobile users under a suitable mobility model for vehicular movement. For this purpose the random waypoint city model is used with five different city maps. The focus lies on the difference in performance resulting from the distinct stationary user distributions of four real city maps and an artificial Manhattan grid. Detailed packet-based simulations using the network simulator ns-2 show the importance of assessing the stationary user distribution before fixing the locations of the wireless access points. The compared factors that are influencing the system's performance include mean data rates, number of users in hotspots as well as mean sojourn-times in hotspots and times in-between coverage. Although the resulting performance of the scenarios is quite diverse, the use of wireless LAN as an access technology for sporadic vehicular Internet usage is possible in all of them

The performance of TCP flows over rate-adaptive wireless LAN (WLAN) is investigated. Therefore, an analytical model of WLAN from our previous work is enhanced to include multiple TCP down-link flows. Modelling TCP's flow and congestion control over rate adaptive WLAN required to solve an M/G/1/B queueing system and a set of non-linear equations. The results are verified with simulations and show that the main performance influencing parameters are the locations of the users and of course the number of these. We show for several scenarios the TCP throughput that users can expect.

Computer simulation is a powerful tool for performance evaluation of new network protocols or dimensioning of communication networks. We show that current processors allow us to drive realistic simulations for medium to large network topologies with more than 110,000 HTTP/TCP clients. We reduce the complexity of the simulations by using a smaller number of clients as compared to reality while increasing the activity of each client and thus keeping the traffic load approximately constant. When evaluating how far the number of clients can be reduced without introducing large errors, we are focusing on the following measures: accuracy of matching a specified (measured) traffic load for each link, coefficient of variation, Hurst parameter, end-to-end delay and loss probability. We show that the only parameter affected by the reduction is the loss rate. Our results show that a significant reduction of the required memory, a factor of 4-8, can be gained by reducing the number of clients and increasing the client activity. A side-effect is a gain in simulation speed of up to 30 %. Nevertheless, the reduction of the required memory makes it possible to perform realistic simulations of large networks topologies on computer systems with hard per process memory limitations.

The Differentiated Services (DiffServ) architecture has been defined for implementing scalable service differentiation in the Internet. DiffServ edge routers employ traffic conditioners that contain meter, marker and shaper functionalities. The way of traffic shaping in traffic conditioners is an open issue and we believe, using intelligent shaping algorithms instead of leaky bucket algorithms (LBA) could increase the network performance significantly. We present two new shaping algorithms for variable packet size networks that emit packet streams which behave in a certain sense better than Poisson streams and compare them to the leaky bucket algorithm (LBA). The introduced shaping algorithms are proven to perform better than LBA and furthermore provide a means to network providers to answer the questions of network dimensioning.

In resource marking theory, users adapt their rates according to their utility functions and congestion signals from the network. Using a special type of utility function, this leads to a proportionally fair rate allocation among the users. We examine the ability of two proposed resource marking implementations, random exponential marking (see Athuraliya, S. et al., Teletraffic Science and Engineering, vol. 4, p.817-28, 2001) and the virtual queue mechanism (see Gibbens, R.J. and Kelly, F.P., Automatica, vol.35, p.1969-85, 1999), to yield a proportionally fair rate allocation. We also propose a third and less complex algorithm, single bit resource marking, that combines the advantages of both.

In this article we present a new class of traffic shapers that make up the shaping decision whether to delay or pass a packet by comparing a measured distribution specifying the arrival stream to a given reference distribution. Rather than simply comparing average values this shaper emits data streams with property 'better than reference distribution' by employing a kind of nonparametric test. If all incoming data streams of the network considered are shaped according to 'better than Poisson', network dimensioning is simplified in the sense that multiplexer performance can be predicted conservatively by assuming Poisson arrivals, hence, admission control and resource dimensioning can be based on a simple M/D/1 queueing model. The presented shaping algorithm thereby provides an analytical tool for network providers to calculate upper bounds on the load in a network fed with accordingly shaped streams only. Our simulations show that the shaper presented emits data streams with corresponding distribution function almost identical to (or better than) reference distribution independent of the input arrival process but on the other hand introduces no serious delays if the arriving stream is already 'better than reference'. Moreover the shaper is mostly robust in terms of shaping parameters and initial conditions and has the capability to remove correlations of the passing stream.

We consider the queue building up in an ATM multiplexer. The cell stream at each input line is modelled as an independent Bernoulli process. Unlike previous work we allow for different average utilizations of each input line. The main result is a closed formula for the queue length distribution.>

A previous BER analysis (see ibid., vol.39, no.11, p.1625, 1991) is based on a Gaussian approximation. We derive a combinatorial BER analysis and an improved Gaussian approximation for synchronous optical code-division multiple-access (S/CDMA) with prime codes. This analysis is shown to be in good agreement with the Gaussian approximation as well as with simulation results.

In this paper a computer simulation model for a land mobile radio fading channel is presented. The model assumes non frequency-selective fading but takes into consideration the effects caused by shadowing. The simulation model is based on an efficient approximation of filtered white Gaussian noise by a finite sum of weighted sinusoids with equally distributed phases. Two completely different methods for the computation of the coefficients of the simulation model are discussed. The design of a fading channel model by one of the presented methods leads always to a simulation model that is completely determined for all time, and therefore, it can be considered as a deterministic model that approximates a stochastic process.

This paper discusses the functional components of nodes in wide-band switching networks. Emphasis is given to the local area where the system's architecture can be considerably simplified. The experimental results are related to this type of application. They demonstrate the availability of all system components for medium-size systems (up to 240 lines). A 16 × 16 highly integrated switch is described as a building block for greater systems. It is capable of handling data streams up to 380 Mbits/s. The maximum jitter amplitude observed after passing one cross point is 0.25 ns.