Native IP multicast would be the best solution to distribute live streaming contents among various destinations since the real-time nature of such applications usually imposes strict delay constraints. Application Layer Multicast (ALM) platforms are emerging as a solution to overcome the well- known lack of a globally supported native multicast. Since the development of ALM applications is slowed by complexity and portability issues, we designed an open source C library framework that takes care of RTP/RTCP technical details and fosters a modular and higher level design. Besides it frees ALM developers from spending time in porting operations from Unix to Windows operating systems.

Peer-to-peer streaming is a well-known technology for the large-scale distribution of audio/video contents. Its widespread adoption derives from the possibility of having a good scalability without the need for the deployment of expensive infrastructures such as Content Delivery Networks (CDNs). We think real-time streaming of lessons could open new interesting opportunities in e-learning systems by encouraging interactivity between teachers and learners. Delay requirements are very strict in interactive e-learning scenarios, where playback lag between the event in the real world and the received audio/video should not exceed a few seconds. Only a very short delay would allow students to ask questions during the lesson. At the same time, playback continuity is a key aspect too, since holes in the stream reproduction could seriously compromise the understanding of lectures. In this paper we compared some solutions that try to overcome the limitations of traditional mesh-based P2P systems, which are usually affected by long and unpredictable delays. We finally tried to outline which of the analyzed solutions appears the most suitable one to meet e-learning requirements.

In this paper we describe the testing activities carried out to evaluate the benefits that the digital educational format implementation ILIADE (“Insegnare L’Informatica A Distanza Efficacemente”, Distance Teaching Computer Science Effectively) provides. The purpose of the ILIADE format is to enable the synchronous delivery of real-time lessons and multimedia contents - provided by one or more teachers - to a virtual classroom. The virtual classroom is the set consisting of both physical remote classrooms - hosting student groups – and individual stations (which are connected to individual students with their own computers). The setup of the virtual classroom allows the learning by doing approach to directly involve students: each student can intervene during the lesson, both dialoguing with the teacher and with his fellow students and share his/her experience with the rest of the class. The collaborative approach in the virtual classroom emphasizes the concepts expressed by the teacher, allowing the participants to improve the understanding and learning of the explained subjects. In ILIADE, multiple technologies are merged to enable real-time interaction between teacher and students, with the opportunity for participants to deal directly with the teacher, even in case of large-scale (large number of participants). This means that the virtual classroom is based on the distribution of audio-stream real-time video of the teacher station to learners, who can send questions to the same by means of a chat class (that is shared among all participants). In the ILIADE format, the subsystem CHARMS is responsible for the delivery of the A/V streamed lesson to all participants, organized into a cooperative overlay for the relaying purposes. This work is part of the project EDOC@ Work3.0.

The paper describes an architecture dedicated to the terrestrial relaying of a real-time IP multicast audio-video stream broadcasted by a satellite. Such relaying is performed by nodes equipped with both a satellite receiver and a terrestrial Internet link. The stream is requested and obtained by sites that are not equipped with satellite receiving hardware but are nonetheless willing to receive it. By exploiting the properties of satellite transmission and adopting an hybrid satellite/terrestrial, multicast/unicast approach the described architecture allows to overcome the restrictions suffered by multicast traffic in the global Internet, allowing it to scale easily across autonomous systems.

In the present work a feasibility study of a novel peer-to-peer architecture for live video streaming is proposed. It leverages both recent web technologies for peer implementation and overlay management, and the use of online social networks as integral part of the architecture itself. The key points of the architecture are: (1) the use of WebRTC to setup and manage a P2P overlay, and to deliver audio/video streams; (2) the implementation of P2P clients as HTML5/Javascript web applications, without involving other centralized entities acting as servers, according to a nearly serverless model; (3) the use of online social networks to retrieve user information and relationships between them, in order to improve overlay and stream management, and as a place to announce their setup and broadcasting, and to increase the audience; (4) the use of social networks to implement the WebRTC signaling. In this paper, after a brief excursus of the involved technologies, the proposed architecture will be introduced, and a first prototype will be presented with the aim of demonstrating the feasibility of the project. The authors will also introduce the elements of the architecture on which future efforts for subsequent enhancements and extensions will be focused.

How many ways to transmit live audio and video to a very large audience are available? While the layman may consider such problem a trivial one, the exact opposite is true. A short review of the answers to the question is given in the following, together with a brief description of the drawbacks associated with each of them. The article ends with a short presentation of a proposal developed in the authorʼs lab which puts to work the Internet and the satellite to get around the difficulties of the reviewed methods.

The paper describes an architecture to relay on demand a real-time IP multicast audio-video stream broadcasted by a satellite on a terrestrial link. The stream is received by suitably equipped sites and then relayed to other sites that are not equipped with satellite receiving hardware but are nonetheless willing to receive the stream. By exploiting the properties of satellite transmission and adopting a hybrid satellite/terrestrial, multicast/unicast approach, the described architecture allows to overcome the restrictions suffered by multicast traffic in the global Internet, allowing it to scale easily across autonomous systems.

The problems involved in multicast key distribution are discussed. Three protocols to accomplish such task are presented (one of them being designed by the authors) and their performances are compared.

In spite of massive research efforts devoted to the advance of the technologies for large-scale live distribution of audio-video IP streams, no totally satisfying solutions seem to have emerged so far. CDNs are still expensive and P2P-TV systems face substantial delay limitations. As the deployment of a global terrestrial IP multicast infrastructure still looks far, turning the attention to satellite-based multicast would seem a sensible choice. However, the cost of such technology has been a stumbling block until now. That is where the CHARMS architecture comes in. It is designed to take advantage of the formidable properties of the satellite without requiring a generic user to install any sort of satellite receiver or dish. Its cornerstone is the recursive terrestrial relaying of satellite streams a number of properly equipped hosts are able to receive. The present paper relates about the results of the OpenSatRelaying project, aimed at the implementation and testing of the CHARMS architecture.

Video quality is a key factor in modern video streaming systems. Video compression artifacts affect it but also delay, jitter and packet loss may compromise it. Objective metrics have been proposed to emulate the human visual system: several experimental works have evaluated their adherence to opinions expressed by real users. Instead of dealing with subjective tests, we focused on the effects of network packet losses on objective metrics: since quality metrics are generally computationally intensive, a convenient approach could consist in inferring information about transmission quality from network impairment statistics. We did experimental tests on two computer-animated videos, whose high color contrasts allow a fair comparison between content dependent and content independent metrics. We studied the encoding parameters that minimize/maximize the values of some metrics (PSNR, BI-PSNR, SSIM, 3SSIM, MSSSIM, VQM) for several packet loss percentages. We analyzed also the Empirical Cumulative Density Function of the degradations of quality metrics

Molti vizi e virtù di Apple hanno le radici in vizi e virtù di Steve Jobs. Questi a loro volta derivano dalla spiccata originalità del suo percorso creativo e professionale e dai problemi piuttosto pressanti che questa ha creato. Ad essi egli ha reagito secondo la sua natura, determinando, in ultima analisi, la fisionomia caratteristica di Apple. Il testo seguente cercherà di illustrare alcuni punti di questa tesi.

In recent years, the fifth revision of the HyperText Markup Language standard (HTML5) has promoted the porting of traditional desktop applications to the Web, thus allowing the rise of Rich Internet Applications (RIAs). Additionally, the progressive support to Web Real-Time Communication (WebRTC) standard in modern browsers for real-time communications is accelerating this process, enabling the migration of a number of complex network applications and services to Web, including peer-to-peer (P2P) overlays. At the same time, the increase of bandwidth in access networks enables end-users to become content producers too. Taking into consideration the aforementioned factors, this paper introduces a preliminary proposal of metrics and technologies to move towards a decentralized cooperative architecture for large scale, real-time live stream content delivery based on WebRTC, with no need of a Content Delivery Network (CDN) infrastructure. Such metrics and technologies are introduced to smooth the way for a transition in such direction of the already described and implemented CHARMS (Cooperative Hybrid Architecture for Relaying Multimedia Streams) architecture.