Quality of Experience Under Huge Load for WebRTC Applications: A Case Study of Three Media Servers

Videoconference applications are becoming increasingly popular, and the demand for these applications is growing. The availability of a standard for building videoconference application on the web, the W3C WebRTC standard, boosted the development of such applications. With so many alternatives available, an impact on quality due to an overload of such applications might cause users to leave and choose another service instead. This makes stress testing mandatory in order to understand the limits of these videoconference solutions and how these limits impact the quality of experience (QoE) of the users. However, most testing tools are not designed to calculate QoE, which is essential for real-time videoconference applications, because QoE calculation is complex and a computationally intensive process. This paper focuses on how load impacts QoE for WebRTC applications and presents OpenVidu QoE and Load Testing Tool (OQLT), a load and stress testing tool for WebRTC applications which measures the QoE of users in videoconference applications. In this work, we make use of this tool to help researchers and practitioners understand the impact of server load on the QoE of users in WebRTC applications, by analyzing three different communication systems: Kurento, Mediasoup, and Pion. We study which quality of service (QoS) metrics can be used to prevent an impact on the QoE of users in these servers. We also analyze different session sizes and topologies to understand the impact of server load on the QoE of users under different circumstances. Our findings show that in two of the three media servers (Kurento and Pion), CPU alone is a good indicator of QoE degradation, whereas for Mediasoup, additional WebRTC metrics are needed, because under high CPU usage Mediasoup can still provide a good QoE to its users. We also found that the behavior of the three media servers under load with respect to the QoE perceived by users is different, which might be important for practitioners, and that not all users are impacted equally by an overload on the server, and how users are impacted under such a load depends as well on the media server. From our extensive analysis of the data collected, we provide detailed implications for practitioners when using WebRTC applications.