Sasho Gramatikov

Stochastic modelling of peer-assisted VoD streaming in managed networks

Video on Demand is the leading service in Internet Protocol Television environments both in popularity and in quantity of generated traffic. Peer-assisted streaming in combination with an optimal distribution of the video contents on the peers has emerged as one of the most accepted solutions by the operators, especially in the privately managed networks, which helps to alleviate the streaming servers. However, an important question in these environments is how the system parameters and the various distributions of the video contents on the peers would impact the overall system performance. In order to give answers to these questions, we propose a precise and flexible stochastic model that takes into consideration parameters like uplink and storage capacity of the peers, number of peers, size of the video content library, size of contents and content distribution scheme to estimate the benefits of the peer-assisted streaming. We use this model as a tool that helps to find the optimal values of these parameters for best performance, as well as the limits of the system for a given configuration.

Game Theoretic Approach for Discovering Vulnerable Links in Complex Networks

Complex networks have been an up-and-coming exciting field in the realm of interactions. With their widespread use appearing on the horizon it is ever more vital to be able to measure their vulnerability as a function of their topology. Precisely, discovering vulnerable links, disposed to attacks, can help in hardening these links and by that providing more secure and reliable network structure. This paper addresses the link vulnerability of different topologies of complex networks such as: random networks, geographic random networks, small world networks and scale-free networks. We introduce measure for vulnerability of complex networks, and prove by simulations that network vulnerability heavily depends on the network topology.

Modelling and analysis of non-cooperative peer-assisted VoD streaming in managed networks

The growing popularity of the Video on Demand service in the Internet Protocol Television environments and the demand for increased quality of the offered videos are becoming a serious threat for the service providers because the high amounts of video traffic are causing congestion in the delivery networks. One of the most acceptable approaches to solve this issue is the peer-assisted streaming, where the peers participate in the streaming process in order to alleviate the load on the streaming servers and in the core of the network. Although the reliability of the Peer-to-Peer service is considerably improved in the managed networks because of the control that the operators have over the clients’ Set-Top Boxes, the failures of the peers still cannot be completely eliminated. The operator can take advantage of the streaming and storage resources of the clients and use them for peer-assisted streaming only while they are watching a video, but not after they finish the streaming session because they may turn off their receiving devices until the next session. In this chapter, we address the issue of the failures of the peers in such environments and their influence on the traffic requested from the servers for providing uninterrupted video experience. For that purpose, we propose a precise mathematical tool for modelling a peer-assisted system for Video on Demand streaming in managed networks with non-cooperative peers, which may decide not to share their resources while they are not active. This tool calculates the performance of the system taking into consideration large variety of system parameters, including the failure probability and the time the peers spend until they decide to turn on the STB and join the network. As the results from the simulations verify the correctness of the mathematical model, we use it to analyse how the failures of the peers are affecting the system’s performance for different system parameters.

Parallel implementation of the modified subset sum problem in CUDA

In the recent years, computing is shifting from “central processing” on the CPU to “co-processing” on the CPU and GPU. This computing paradigm shift is due to the development of CUDA (Compute Unified Device Architecture) parallel computing architecture. CUDA is a programming model for parallel computing in Graphics Processing Units (GPUs). In this work, we have implemented parallel solution of the NP-complete modified subset sum algorithm using CUDA. With our implementation, for a certain problem size, we have obtained speedup of 20 times, compared to the CPU version.

P2P Assisted Streaming for Low Popularity VoD Contents

The Video on Demand (VoD) service is becoming a dominant service in the telecommunication market due to the great convenience regarding the choice of content items and their independent viewing time. However, due to its high traffic demand nature, the VoD streaming systems are faced with the problem of huge amounts of traffic generated in the core of the network, especially for serving the requests for content items that are not in the top popularity range. Therefore, we propose a peer assisted VoD model that takes advantage of the clients unused uplink and storage capacity to serve requests for less popular items with the objective to keep the traffic on the periphery of the network, reduce the transport cost in the core of the network and make the system more scalable.

Energy Dependent Connection Availability Model for Ad Hoc Networks

Although wireless networks have existed for many years already, explicit concern about their energy efficient operation has emerged only recently with the proliferation of lightweight mobile devices. In this paper we propose an energy dependent connection availability model for ad hoc networks which relies on a number of real measurable parameters. The model provides the means to analyze and optimize the energy consumption in the ad hoc network while taking into consideration the nodes connectivity and the limited battery capacity with possibilities for recharging

Network Topology Impact on Influence Spreading

Networks composed of large number of nodes interacting in structured ways such as power grids, communication networks, social networks or market networks are critical port of the world’s infrastructure. Many times minor changes of the sate in some of the nodes can spread rapidly and cause major effects in the network, so understanding the behavior of the complex network due to changes of the state is of a great interest. In this paper we present influence spreading in networks driven by the influence model. We also show how the topology and connectivity of a network affect the spread of influence.