Modeling stability and bitrate of network-assisted HTTP adaptive streaming players

Viewers using HTTP Adaptive Streaming (HAS) without sufficient bandwidth undergo frequent quality switches that hinder their watching experience. This situation, known as instability, is produced when HAS players are unable to accurately estimate the available bandwidth. Moreover, when several players stream over a bottleneck link, their individual adaptation techniques may result in an unfair share of the channel. These are two detrimental issues in HAS technology, which is otherwise very attractive. To overcome them, a group of solutions are proposed in the literature that can be classified as network-assisted HAS. Solving stability and fairness only in the player is difficult, because a player has a limited view of the network. Using information from network devices can help players in making better adaptation decisions. In this paper we describe our implementation in the form of an HTTP proxy server. We show that with this proxy server both stability and fairness are improved. Furthermore, we present an analytical performance model that allows to accurately compute the number of changes in video quality and the bitrate of a video stream. The performance results of the HAS assisting proxy server, a real implementation, are used to validate our performance model. We believe that this model substantially eases future research of video delivery networks that use in-network HAS assistants. Using our model we are able to analyze stability and bitrate of HAS streams prior to real deployment, which saves time and money.