Abstract
Peer-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.
Highlights
Peer-to-peer (P2P) streaming has been introduced to distribute live or on-demand multimedia content over the Internet: end systems receiving a video stream simultaneouslyMultimedia Tools and Applications (2021) 80:20929–20970 upload that stream or some parts of it to other nodes, becoming peers in an application layer structure called overlay
We considered a single-tree overlay as a pilot study, but the experiments we have conducted could provide useful performance insights for other topologies: our approach based on lock-free data structures can provide significant performance improvements every time there is the need to rearrange the connections among nodes, regardless of the employed overlay topology
The time for restoring the stream reception is the parameter that highly benefits from the lock-free design, since it is reduced even by three orders of magnitude compared to the value in the lock-based version
Summary
Peer-to-peer (P2P) streaming has been introduced to distribute live or on-demand multimedia content over the Internet: end systems receiving a video stream simultaneouslyMultimedia Tools and Applications (2021) 80:20929–20970 upload that stream or some parts of it to other nodes, becoming peers in an application layer structure called overlay. Tree-based overlays propagate multimedia contents through a tree graph rooted in a streaming source. Real-time scenarios require a low end-to-end delay between the streaming source and any receiving node. A particular subcategory of real-time streaming applications consists in interactive applications, which are the main target of our research work. They impose even more strict requirements on delay and playback continuity, which means the ability to play a stream with no interruption or frame freezing. This is the case, for instance, of e-learning scenarios. Playback continuity is very important to allow a good understanding of a lecture: network congestion and physical link problems may cause interruptions or severe QoS degradations in the stream propagation over the Internet
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