Algoritmo Adaptativo de Retransmissão Seletiva para Distribuição de Vídeo em Redes Sobrepostas

Carlos Eduardo LenzLau Cheuk LungFrank Siqueira

With the widespread adoption of broadband Internet access, home users have started to consume several multimedia services, such as IP Telephony, radio and video on demand. Meanwhile, the main video services are on-demand and need buffering, while TV is live. They also require a server bandwidth that grows linearly with the number of clients. IP Multicast does not have this bandwidth problem, but is unavailable, so overlay networks are used. Nonetheless, these networks do not specify the packet loss handling: ignore or recover and how. After the analysis on the properties of the H.264 standard for digital video compression, this work presents clear criteria for retransmission based on the several different types of frame coding. It establishes priorities among these types and defines an algorithm for the selection of lost parts for recovery. The algorithm uses a movable target, lowering the target each time the retransmission of a segment is requested. To test it, an overlay network (SeRViSO) is used, comparing the algorithm to another where the target is fixed. The advantages of a clear loss handling are the greater adaptation to the network conditions and less important losses, which do not propagate error for many frames.

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