Software-defined networking (SDN) logically separates the control and data planes, thus opening the way to more flexible configurations and management of low-Earth orbit (LEO) satellite networks. Since one or, more generally, multiple distributed controllers are needed, a significant challenge in SDN is the controller placement problem (CPP). Due to characteristics such as the dynamic network topology, limited bandwidth and traffic variations, the CPP is quite complex in SDN-based satellite networks. In this paper, we propose solving the CPP by means of a static placement with dynamic assignment (SPDA) method for LEO satellite networks. The SPDA method has two parts: the first is to incorporate SDN controllers into some fixed satellites by formulating a mixed integer programming model; the second is to dynamically assign switches to existing controllers according to the switch-controller latency and the traffic load of controllers. The SPDA method takes the topological dynamics into account by effectively dividing time snapshots, and it has a lower bandwidth consumption compared with methods involving controller migrations. Real satellite constellations are used to evaluate the performance of our controller placement solution. The results show that SPDA outperforms existing methods in terms of reducing the switch-controller latency, and it also has good load balancing performance.

Using satellite constellations to provide global Internet access services has recently drawn increasing attention. A low-Earth orbit (LEO) satellite network with multiple satellites provides global coverage, low latency, and operates independently, by which it effectively complements terrestrial IP networks. Satellite gateways are located on the ground and can serve as data exchange points between satellite networks and the Internet. As the placement scheme can affect network performance, finding appropriate sites for gateways constitutes a fundamental problem. This paper proposes a gateway placement optimization (GPO) method for LEO satellite networks in order to solve this problem by modeling it as a combination optimization problem. We aim to identify the best gateway locations that can balance traffic loads while using as few gateways as possible. The constraints to be satisfied concern the physical links between gateways and satellites: specifically, link interference, satellite bandwidth, and number of satellite antennas. We use a gravity model to estimate the traffic matrix from/to gateways and satellites, then we adopt and modify the discrete particle swarm optimization (PSO) algorithm to solve this problem. Finally, we apply the GPO method to numerical tests on real satellite constellations. The results indicate that our method performs well and effectively.

Fueled by advances in multi-party communications, increasingly mature immersive technologies being adopted, and the COVID-19 pandemic, a new wave of social virtual reality (VR) platforms have emerged to support socialization, interaction, and collaboration among multiple remote users who are integrated into shared virtual environments. Social VR aims to increase levels of (co-)presence and interaction quality by overcoming the limitations of 2D windowed representations in traditional multi-party video conferencing tools, although most existing solutions rely on 3D avatars to represent users. This article presents a social VR platform that supports real-time volumetric holographic representations of users that are based on point clouds captured by off-the-shelf RGB-D sensors, and it analyzes the platform’s potential for conducting interactive holomeetings (i.e., holoconferencing scenarios). This work evaluates such a platform’s performance and readiness for conducting meetings with up to four users, and it provides insights into aspects of the user experience when using single-camera and low-cost capture systems in scenarios with both frontal and side viewpoints. Overall, the obtained results confirm the platform’s maturity and the potential of holographic communications for conducting interactive multi-party meetings, even when using low-cost systems and single-camera capture systems in scenarios where users are sitting or have a limited translational movement along the X, Y, and Z axes within the 3D virtual environment (commonly known as 3 Degrees of Freedom plus, 3DoF+).

Social Virtual Reality (VR) allows multiple distributed users getting together in shared virtual environments to socially interact and collaborate. This article explores the applicability and potential of Social VR in the broadcast sector, focusing on a live TV show use case, by providing three main contributions: 1) a novel and lightweight social VR platform; 2) a professional piece of VR content to recreate an interactive live TV show; and 3) an analysis of the performance and user experience. The Social VR platform includes different innovative and outstanding features compared to state-of-the-art solutions. It allows a real-time integration of remote users in shared virtual environments, using realistic volumetric representations and affordable capturing systems, thus not relying on the use of synthetic avatars. It supports a seamless and rich integration of heterogeneous media formats, including 3D scenarios, dynamic volumetric representation of users and (live/stored) stereoscopic 2D and 180°/360° videos. In addition, it enables low-latency interaction between volumetric users and a video-based presenter (Chroma keying) and a dynamic control of the media playout to adapt to the session’s evolution. The article also describes the production process of an immersive an interactive TV show to demonstrate the platform’s capabilities and its potential benefits. On the one hand, the results from objective tests show the satisfactory performance of the platform. On the other hand, the promising results from user tests support the potential impact of the presented platform, opening up new opportunities in the broadcast sector.

DCell~\cite{guo} has been proposed as a server centric network structure for data centers. DCell can support millions of servers with high network capacity and provide good fault tolerance by only using commodity mini- switches. However, the traffic in DCell is imbalanced in that links at different layers carry very different number of flows. In this paper, we present a generalized DCell framework so that structures with different connecting rules can be constructed. We show that these structures still preserve the desirable properties of the original DCell structure. Furthermore, we show that the new structures are more symmetric and provide much better load- balancing when using shortest-path routing. We demonstrate the load- balancing property of the new structures by extensive simulations.