A control theory based rate adaption scheme for dash over multiple servers

Recently, Dynamic Adaptive Streaming over HTTP (DASH) has been widely deployed in the Internet. However, the research about DASH over Multiple Content Distribution Servers (MCDS) is few. Compared with traditional single-server-DASH, MCDS are able to offer expanded bandwidth, link diversity, and reliability. It is, however, a challenging problem to smooth video bitrate switchings over multiple servers due to their diverse bandwidths. In this paper, we propose a block-based rate adaptation method considering both the diverse bandwidths and feedback buffered video time. Multiple fragments are grouped into a block, and the fragments are downloaded in parallel from multiple servers. We propose to adapt video bitrate at the block level rather than at the fragment level. By dynamically adjusting the block length and scheduling fragment requests to multiple servers, the requested video bitrates from the multiple servers are synchronized, making the fragments downloaded orderly. Then, we propose a control-theoretic approach to select an appropriate bitrate for each block. By modeling and linearizing the rate adaption system, we propose a novel Proportional-Derivative (PD) controller to adapt video bitrate with high responsiveness and stability. Theoretical analysis and extensive experiments on the Internet demonstrate the good efficiency of our DASH designs.