Franco Tommasi

Experience-driven selective scan for 802.11 networks

The current use of the IEEE 802.11 protocol does not fully meet the full requirements of real-time applications. During the handoff period the STA cannot receive traffic and the quality of these applications is therefore reduced. A significant cause of this latency is that the STA normally scans all possible channels before synchronizing one of them. Considering that normally several channels are empty and that the 802.11 infrastructure architecture provides for fixed access points, it is possible to reduce the overall latency by reducing the number of channels to be scanned. In this paper we show an algorithm for selectively scanning just one probable channel. If such a channel is not available, the algorithm selects a second candidate until it scans all channels. These probabilities depend on the movements inside that LAN of previous STA. We show motivations and specifications of the algorithm

Design of the satellite reliable distribution protocol (SRDP)

In this paper we propose and discuss the satellite reliable distribution protocol (SRDP), a novel protocol designed for satellite-based data broadcasting. This protocol aims to transmit reliable multicast information of Internet applications in an efficient and scalable way. We discuss the requirements of the protocol analysing the main issues given by the possible use in the global Internet. The solution we present is based on a cooperation between receivers that improve the overall behaviour. The performances of the protocol are evaluated by the mean of ns2 - network simulator.

Packet losses and objective video quality metrics in H.264 video streaming

We analyzed PSNR, BIPSNR, SSIM, 3SSIM, MSSSIM, VQM for various packet loss fractions.A lower bitrate mitigates PSNR impairments caused by packet losses.BIPSNR has less probability than PSNR to be significantly influenced by packet losses.Among structural similarity metrics, SSIM is the least affected by packet losses.VQM metric is the most affected by packet losses. 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.

OpenSatRelaying: a Hybrid Approach to Real-Time Audio- Video Distribution over the Internet

 Abstract—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.

CHARMS: Cooperative hybrid architecture for relaying multicast satellite streams to sites without a satellite receiver

This 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.

Are P2P streaming systems ready for interactive e-learning?

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.

The Campus Satellitare del Salento: a scalable and transparent e-learning application

The CSS (Campus Satellitare del Salento) is an e-learning application developed by the University of Lecce (in Italy) that integrates live, interactive and on-demand services over not only the Internet but also the satellite infrastructure. This paper presents the CSS realized as a solution to face the problem of guiding large classrooms of students and of developing didactic models very transparent like traditional ones. As such, CSS gains scalability making use of a satellite data network and of a remote monitoring tool. Moreover, transparency is obtained using screen-recording and open learning environment in which the learning material (multimedia data) is organized into an easy and a modular structure. Even though these solutions have been adopted to solve a local problem, it seems to have a wide range of potential implementations

Towards a decentralized overlay for real-time live streaming: CHARMS meets the web

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.

SRDP-Sign: a reliable multicast protocol for signaling

In this paper we present SRDP-sign, a reliable multicast protocol designed to guarantee the reliable transmission of short messages via satellite as an extension of satellite reliable distribution protocol (SRDP). The uses of this protocol range from sending short text messages to transmitting information used for the improvement of networkspsila performances. The innovation of this protocol is that it has a high degree of scalability, reduced communication with receivers and fast delivery. In this paper we show the operations of the protocol, the underlying algorithms and analyse the protocolpsilas behavior.

Efficient multi-source RTP stream relaying in overlay networks

P2P streaming systems exploit the high scalability of P2P networks to propagate multimedia streams to wide areas in a distributed fashion. A P2P network is made up of several logic connections among peer nodes, which can form a mesh or a tree overlay. Interactive real-time streaming imposes very strict delay constraints: in e-learning environments, for instance, only a high level of synchrony with the live event may allow users to ask questions in real-time to the lecture speaker. Despite their resilience to peer churning, mesh overlays are affected by a high and variable delay, which hampers their adoption in interactive applications. Playback discontinuity, caused by missing chunks, may be a serious problem too, since it may compromise the speech understanding. On the contrary, multi-tree MDC-based overlays can guarantee a smooth playback continuity, since a stream can be fluently reproduced also when some descriptions are lost. The queuing and the elaboration delay of the nodes should be kept under control to reduce the overall end-to-end delay on each tree branch. In this work we describe a framework for the construction of reliable tree overlays: we designed a smooth switch-to-fallback mechanism to quickly replace nodes leaving the overlay, a channel for packet recovery and a very efficient engine that collects MDC descriptions coming from parent nodes. The experimental data we reported in the last section reveal a low CPU usage and a very low elaboration delay in collecting MDC descriptions.