Nowadays, many application layer multicast protocols (ALM) in which Multiple Description Coding (MDC) is introduced have been proved to be more scalable and stable than traditional multicast protocols in practical environment. In this paper, we propose an ALM system called SMSD based on synchronized MDC for streaming media to address the synchronization of available descriptions. SMSD focuses on the video quality, firstly hosts can join the different overlay trees in different layers simultaneously, then the maximum covering set is worked out based on acquired descriptions information to achieve the best video quality, the quality management module with much low overhead is responsible for monitoring the variation of cached content due to departure of parents and activating the re-join procedure. Simulations implemented on Internet-like topology indicate that SMSD achieves higher video quality, lower control traffic than traditional ALM protocols, and comparable latency, link stress and robustness are achieved as well.
