QoS monitoring in real-time streaming overlays based on lock-free data structures

AbstractPeer-to-peer streaming is a well-known technology for the large-scale distribution of real-time audio/video contents. Delay requirements are very strict in interactive real-time scenarios (such as synchronous distance learning), where playback lag should be of the order of seconds. Playback continuity is another key aspect in these cases: in presence of peer churning and network congestion, a peer-to-peer overlay should quickly rearrange connections among receiving nodes to avoid freezing phenomena that may compromise audio/video understanding. For this reason, we designed a QoS monitoring algorithm that quickly detects broken or congested links: each receiving node is able to independently decide whether it should switch to a secondary sending node, called "fallback node". The architecture takes advantage of a multithreaded design based on lock-free data structures, which improve the performance by avoiding synchronization among threads. We will show the good responsiveness of the proposed approach on machines with different computational capabilities: measured times prove both departures of nodes and QoS degradations are promptly detected and clients can quickly restore a stream reception. According to PSNR and SSIM, two well-known full-reference video quality metrics, QoE remains acceptable on receiving nodes of our resilient overlay also in presence of swap procedures

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

Charms for e-learning: a case study

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