In this work, we study hitting times for the appearance of a spanning structure in the Erdős-Rényi random directed graph processes. Namely, we are concerned with the appearance of an arborescence, a spanning digraph in which, for a vertex u called the root and any other vertex v, there is exactly one directed path from u to v. Let D(n, 0), D(n, 1),..., D(n, n(n - 1)) be the random digraph process where for every m ∈ {0,..., n(n - 1)}, D(n, m) is a digraph with vertex set {1,...,n}; D(n, 0) has no arcs and, for 1 ≤ m ≤ n(n - 1), the digraph D(n,m) is obtained by adding an arc to D(n,m - 1), chosen uniformly at random among the not present arcs. In this paper we determine the hitting time for the existence of k arc-disjoint arborescences when k = k(n) ⩽ log n.

Several works study the performance of Content Delivery Networks (CDNs) under various network infrastructure and demand conditions. Some go even further while considering demand elasticity by leveraging on Cloud elasticity where each Content Service Provider (CSP) is served only the amount of storage space and network throughput that it needs and pays accordingly. Many of today's CDN implementations are based on these proposals. However, the allocation of virtual servers in cloud computing is not yet very fine-grained and suffers from limitations and time constraints for reallocation. This work proposes an efficient cache slicing mechanism that frees the CDN provider from dedicating a different virtual surrogate for each CSP in each location. This is achieved by dealing internally with the allocation space for each CSP in a shared surrogate, while still providing services in terms of network storage allowing a CSP to select and pay the amount of content that can be stored. We show that the proposed approach deals better with peak surrogate usage, and reduces the total network traffic by around 15% and cross-traffic by as much as 35% under some scenarios.

Content Delivery Networks have gained a popular role among application service providers (ASPs) and infrastructural companies. A CDN is an overlay network that gives more control of asset delivery by strategically placing servers closer to the enduser, reducing response time and network congestion. Many strategies have been proposed to deal with aspects inherent to the CDN distribution model. Though mostly very effective, a traditional CDN approach of statically positioned elements often fails to meet quality of experience (QoE) requirements when network conditions suddenly change. In this paper, we introduce a technique to detect significant changes in a monitored metric of a CDN in order to allow provisioning adaptation of resources, using easy access information with great practical viability. Results show decrease on network resources usage without considerable changes on quality of service (QoS). Furthermore, our technique has similar performance in comparison to an omniscient strategy.

The BitTorrent protocol is one of the most successful P2P applications, being largely studied by the research community. Nevertheless, studying the dynamics of a large BitTorrent network presents several challenges, such as difficulty in acquiring network traces or building measurement experiments. Evaluation through simulation is usually utilized for studying BitTorrent networks, yet only a few BitTorrent simulation models are available for the research community. In this article, we present an extensible framework for developing BitTorrent simulations, focusing on realism and without losing on scalability. We developed an accurate version of the protocol by analyzing the source code of mainstream BitTorrent clients and by discussing directly with their developers. The simulation model was developed with the OMNeT++ Framework, inheriting its high extensibility, and with the INET Framework, for accuracy of the underlying network model. We also took into account the effects of multitasking in our model, since BitTorrent applications acquires content from several sources simultaneously, and utilized real world traces for modeling the processing times. We present an analysis of our simulator regarding performance aspects and BitTorrent-related results.

Peer-to-peer (P2P) networks have in the past years become a very attractive method for delivery of media content over the Internet. Many factors have contributed to this success, but the low delivery costs and the inherent scalability of the P2P networks whereby consumers of content are also potential sources are among the most prominent ones. However, the effectiveness and performance of many popular P2P networks (such as BitTorrent based ones) is highly dependent on how well trackers select peers that will provide a content. The peers chosen by a tracker will directly affect the user-perceived performance of the service and the usage of network resources. Moreover, P2P networks have usually no locality awareness, resulting in sub-optimal utilization of network resources. In order to address these issues, we propose a novel hierarchical architecture for P2P locality targeted at managed P2P networks based on the BitTorrent protocol. We then show, through experimentation, that the adoption of the proposed architecture leads to significant network efficiency improvements without compromising end-user experience.

From the four basic functionalities of video delivery systems - linear TV, video on demand (VoD), time-shifted TV (tsTV), and network personal video recorder (nPVR) - most of today's solutions focus either on linear TV, or on VoD. While linear TV usually uses efficient distribution mechanisms such as multicast, VoD is often realized via centralized, bandwidth- inefficient unicast. Even when file sharing P2P algorithms are used for VoD or nPVR, they can not be applied to tsTV since they require the whole content to exist from the beginning. With this paper, we propose a novel solution that aims at offering all four functionalities in one distributed system. Our architecture uses multicast for the distribution of live content, and a modified P2P protocol for offering VoD, nPVR, and tsTV altogether.

This paper examines the issues encountered by network operators when content providers utilize peer-to-peer (P2P) technologies to distribute media. After outlining the various causes of the conflict a set of potential solutions are presented.