This editorial introduces the first part of the Special Issue on “Advanced Technologies in the Decentralized Web.” As the Internet evolves toward more user-centric and resilient architectures, concepts like Web3 and Web 3.0 have gained significant prominence. This issue explores key advancements including decentralized machine learning, AI-blockchain integration, identity management, and data sovereignty. We provide an overview of the selected papers, highlighting their contributions to creating a more transparent and secure decentralized digital future.

International audience

In the Web3 ecosystem, multimedia applications exhibit significant potential by leveraging decentralization, regarded as the core spirit of Web3. This survey aims to provide a comprehensive overview of the potential of decentralization in shaping multimedia applications in the Web3 ecosystem. Through a systematic review of the academic research conducted over the past decade on Web3 decentralization, we identify the two key distinctive decentralization characteristics (decentralized assets and decentralized participation). Subsequently, we comprehensively analyze Web3 applications from both technology and application dimensions. Building upon this, we focus on multimedia-related aspects and propose an architecture for Web3 multimedia applications. In contrast to the broader scope of Web3 applications, the unique aspects of Web3 multimedia applications reside in their core application components (non-fungible tokens and smart contract-based rules) and core application domains (art, games, and social media). Based on this architecture, we provide a precise definition of Web3 multimedia applications. Lastly, through the lens of the two identified distinctive decentralization characteristics, we investigate the advantages, development, and limitations of Web3 multimedia applications within the three core application domains, namely crypto art, blockchain games, and blockchain on social media (BOSM). Furthermore, we share our insights into several promising yet challenging directions, covering the interoperability and potential of increasingly valuable multimedia content, as well as the delicate balance between centralization and decentralization.

The metaverse, as a rapidly evolving socio-technical phenomenon, exhibits significant potential across diverse domains by leveraging Web3 (a.k.a. Web 3.0) technologies such as blockchain, smart contracts, and non-fungible tokens (NFTs). This survey aims to provide a comprehensive overview of the Web3 metaverse from a human-centered perspective. We (i) systematically review the development of the metaverse over the past 30 years, highlighting the balanced contributions from its core components: Web3, immersive convergence, and crowd intelligence communities, (ii) define the metaverse that integrates the Web3 community as the Web3 metaverse and propose an analysis framework from the community, society, and human layers to describe the features, missions, and relationships for each community and their overlapping sections, (iii) survey the state-of-the-art of the Web3 metaverse from a human-centered perspective, namely, the identity, field, and behavior aspects, and (iv) provide supplementary technical reviews. To the best of our knowledge, this work represents the first systematic, interdisciplinary survey on the Web3 metaverse. Specifically, we commence by discussing the potential for establishing decentralized identities (DID) utilizing mechanisms such as profile picture (PFP) NFTs, domain name NFTs, and soulbound tokens (SBTs). Subsequently, we examine land, utility, and equipment NFTs within the Web3 metaverse, highlighting interoperable and full on-chain solutions for existing centralization challenges. Lastly, we spotlight current research and practices about individual, intra-group, and inter-group behaviors within the Web3 metaverse, such as Creative Commons Zero license (CC0) NFTs, decentralized education, decentralized science (DeSci), and decentralized autonomous organizations (DAO). Furthermore, we share our insights into several promising directions, encompassing three key socio-technical facets of Web3 metaverse development.

No abstract available.

International audience

While cloud servers provide a tremendous amount of resources for networked video applications, most successful stories of cloud-assisted video applications are presentational video services, such as YouTube and NetFlix. This article surveys the recent advances on delay-sensitive video computations in the cloud, which are crucial to cloud-assisted conversational video services, such as cloud gaming, Virtual Reality (VR), Augmented Reality (AR), and telepresence. Supporting conversational video services with cloud resources is challenging because most cloud servers are far away from the end users while these services incur the following stringent requirements: high bandwidth, short delay, and high heterogeneity. In this article, we cover the literature with a top-down approach: from applications and experience, to architecture and management, and to optimization in and outside of the cloud. We also point out major open challenges, hoping to stimulate more research activities in this emerging and exciting direction.

Gaming on demand is an emerging service that has recently started to garner prominence in the gaming industry. Cloud-based video games provide affordable, flexible, and high-performance solutions for end-users with constrained computing resources and enables them to play high-end graphic games on low-end thin clients. Despite its advantages, cloud gaming's Quality of Experience (QoE) suffers from high and varying end-to-end delay. Since the significant part of computational processing, including game rendering and video compression, is performed in data centers, controlling the transfer of information within the cloud has an important impact on the quality of cloud gaming services. In this article, a novel method for minimizing the end-to-end latency within a cloud gaming data center is proposed. We formulate an optimization problem for reducing delay, and propose a Lagrangian Relaxation (LR) time-efficient heuristic algorithm as a practical solution. Simulation results indicate that the heuristic method can provide close-to-optimal solutions. Also, the proposed model reduces end-to-end delay and delay variation by almost 11% and 13.5%, respectively, and outperforms the existing server-centric and network-centric models. As a byproduct, our proposed method also achieves better fairness among multiple competing players by almost 45%, on average, in comparison with existing methods.

On-demand video streaming applications are attracting an ever-growing number of users on the Internet. As new terminals, and especially mobile ones, give their users the ability to film and edit videos, it is necessary to provide efficient and scalable solutions that enable users to share their creations with as many users as they want. Traditional client-server-based video streaming solutions can no longer cope with the ever-increasing number of users as they incur highly expensive bandwidth provision cost on the server. This paper addresses these issues for on-demand video streaming by proposing a dual spatially-organized peer-to-peer network. The idea is to distribute video streaming load by allowing real-time cache sharing between peers that are viewing approximately the same portion of the stream. Compared to existing P2P video streaming solutions, our solution (1) provides higher efficiency by connecting users who are watching almost the same part of the video, thus increasing the chance of finding missing video chunks at neighboring users, (2) reduces inter-ISP video traffic by privileging content exchange among peers within the same ISP network, and (3) provides incentives to share content by providing different service levels to users with different contributions to the system. Performance evaluations show the self-scalability of our solution in face of mass arrivals of users requesting the same video stream.

Cloud gaming is an emerging service that has recently started to garner prominence in the gaming industry. Since the significant part of computational processing, including game rendering and video compression, is performed in data centers, controlling the transfer of information within the cloud has an important impact on the quality of cloud gaming services. In this paper, we make two contributions: we propose a design to apply the recent paradigm of Software Defined Networks (SDNs) to Cloud Gaming, and we propose an SDN controller that reduces end-to-end delay and delay variations experienced by players. Our SDN controller adaptively disperses the game traffic load among different network paths according to their corresponding end-to-end delays. Experimental results show that our proposed controller reduces end-to-end delay and delay variation by almost 9% and 50% respectively without engendering additional packet loss, compared to a representative conventional method: Open Shortest Path First (OSPF). These reductions lead to improvements in players' gaming experience.

Cloud gaming, the newest entry in the online gaming world, leverages the well-known concept of cloud computing to provide real-time gaming services to players. The idea in cloud gaming is to capture the game events from players and transmit them to the cloud, process those events and run the game logic in the cloud, render the game scene as video in the cloud, and stream that video to the players. The advantage is that as long as the client can display video, which pretty much all smartphones, tablets, game consoles, desktops, laptops, and mobile devices today do, the user can play the game without installing it locally, and without needing to have a machine with high-grade 3-D graphics rendering and powerful computing hardware and software. This makes cloud gaming accessible to a huge market of mass consumers. While some variations of cloud gaming systems stream 3-D graphics, in addition to or instead of video, the great majority of cloud gaming implementations are video based. Using the well-known concept of software as a service, cloud gaming is also sometimes referred to as gaming as a service, which is already available as commercial products, such as Sony’s PlayStation Now, Ubitus’s GameNow, G-Cluster, Crytek’s GFACE, PlayGiga, and LiquidSky, to name a few. There are also many efforts concentrating specifically on the underlying technology behind cloud gaming, such as NVIDIA’s Grid, OTOY, CiiNow, Kalydo, and GamingAnywhere [4], the latter being the only open source and free technology. Microsoft is also exploring cloud gaming technologies, with recent successes such as its Kahawai project [1].

In this paper, we propose a synchronous multihop architecture (SYMA) for wireless ad hoc multiplayer games. In SYMA, devices are assumed to have one-hop neighbor device information, as well as timers synchronized with good accuracy. A player, called game initiator, broadcasts an invitation message to invite other players to join a new game. A joining player issues a message along with its neighborhood information, including the expected transmission time (ETT) for each neighbor node, to reply to the invitation so that the initiator can derive the topology of the participating players. The initiator applies Floyd-Warshall shortest path algorithm, taking the topology and ETT values as input to construct the shortest path spanning tree rooted at each player (or node). It then calculates the expected broadcast time (EBT) for each tree, which is useful to estimate the time for the root node of a tree to broadcast a game state to all tree nodes. Finally, the tree with the smallest EBT is selected as the communication tree and its root is designated as the coordinator, which collects time stamped actions of each player, executes the game logic, and then broadcasts the new game state. By exploiting synchronized timers, the game state consistency is guaranteed, and each node can be scheduled to send/receive game messages without causing collisions.

Peer-to-peer (P2P) architectures have recently become a popular design choice for building virtual environments (VEs). In P2P-based VEs, peer connectivity between the different VE users depends on their positions in the virtual world regardless of the underlying physical network, which is subject to redundant hops and delay. In this paper, we propose Tri-Cast, a fully-distributed P2P architecture to support virtual environment applications by combining a triangular logical network used for discovering the interest group of an event in the virtual world with an application layer multicast support, used for multicasting the event message to the group members. Simulation results show that the proposed physical multicast tree algorithm reduces the cost of message transmission to group members.

Peer-to-peer (P2P) architectures have recently become very popular in massively multiplayer games (MMGs). While P2P gaming offers high scalability compared to client/server architectures, it introduces several major issues related to data distribution and game state consistency. In this paper, we report our initial version of VoroGame, a P2P architecture for MMGs that addresses these issues by combining a structured P2P overlay based on a distributed hash table (DHT) for data distribution, with a Voronoi diagram used for virtual game world decomposition and semantic overlay support. The resulting hybrid architecture enables a fully distributed management of data and state information, and ensures efficient dissemination of game state updates to relevant peers.

This paper proposes a fully distributed architecture to support massively multiplayer games (MMGs) on a peer-to-peer (P2P) overlay network. P2P networks provide a scalable and robust solution for MMGs. Furthermore, similarly to real world interactions, MMG players interact with their surrounding, i.e., with visible players and objects in the virtual world. Thus, self-organization of peers based on their visibility property is essential for efficient overlay network support in MMGs. Also, the overlay network must be re-organized consistently in the face of players' position changes. In this paper, we achieve these goals by designing a peer-to-peer overlay network based on the Voronoi diagram. Each player has a responsibility region that includes nearby objects, and is responsible for updates' dissemination occurring in this region to provide game state consistency among the players who are concerned by the updates. As a proof of concept, we simulated a simple game application to demonstrate the feasibility of our architecture.

Peer-to-peer (P2P) architectures have recently become a popular design choice to build scalable Networked Virtual Environments (NVEs). While P2P architectures offer better scalability than server-based architectures, efficient distribution and management of avatar and object states remains a highly challenging issue. In this paper, we propose GROUP, a fully-distributed P2P architecture for NVEs that addresses this issue by combining a structured P2P overlay, used for object state management, with a Voronoi-based overlay, used for avatar state and group membership management. The resulting dual overlay architecture enables efficient and fully distributed management of state updates for P2P-based NVEs.

The general craze for virtual environments, the potential of augmented reality applications and the announced revolution of the Internet world (Web 2.0, Web 3D.0) are key points for the emergence of an 'ambient' Web which will make it possible for users to communicate, collaborate, entertain, work and exchange content. In this context, content storage, delivery, and reproduction are among the essential points for the deployment of a highly scalable platform of wide reality. In this paper, we propose a self-scalable peer-to-peer architecture for the navigation in network-based virtual worlds. To reach this goal, we propose a fully distributed and adaptive streaming method that quickly adapts the reproduced content according to user interaction. Our content delivery strategy has been implemented and tested on a dedicated simulator with a large 3D city model. The presented results show the efficiency of our strategy in very critical conditions.

The general craze for virtual environments, the potential of augmented reality applications and the announced revolution of the Internet world (Web 2.0, Web 3D.0) are key points for the emergence of an 'ambient' Web which will make it possible for users to communicate, collaborate, entertain, work and exchange content. In this context, content storage, delivery, and reproduction are among the essential points for the deployment of a highly scalable platform of wide reality. In this paper, we propose a self-scalable peer-to-peer architecture for the navigation in network-based virtual worlds. To reach this goal, we propose a fully distributed and adaptive streaming method that quickly adapts the reproduced content according to user interaction. Our content delivery strategy has been implemented and tested on a dedicated simulator with a large 3D city model.

Although widely used in distributed transactional systems, the so-called Two-Phase Commit (2PC) protocol introduces a substantial delay in transaction processing, even in the absence of failures. This has led several researchers to look for alternative commit protocols that minimize the time cost associated with coordination messages and forced log writes in 2PC. In particular, variations of a One-Phase Commit (1PC) protocol have recently been proposed. Although efficient, 1PC is however rarely considered in practice because of the strong assumptions it requires from the distributed transactional system. The aim of the paper is to better identify and understand those assumptions. Through a careful look into the intrinsic characteristics of 1PC, we dissect the assumptions underlying it and we present simple techniques that minimize them. We believe that these techniques constitute a first step towards a serious reconsideration of 1PC in the transactional world.