Scheduling Uplink Bandwidth in Application-layer Multicast Trees
Zegura, Ellen W.
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Many applications can benefit from the use of multicast to distribute content efficiently. Due to the limited deployment of network-layer multicast, several application-layer multicast schemes have been proposed. In these schemes, the nodes in the multicast tree are end systems which are typically connected to the network by a single access link. Transmissions to the children of a node in the multicast tree have to share this single uplink, a factor largely ignored by previous work.In this work, we examine the effect of access link scheduling on the latency of content delivery in a multicast tree. Specifically, we examine the general case where multiple packets (comprising a block of data) are sent to each child in turn. We provide an analytical relation to compute the latency at a node in the multicast tree and show the relationship to the packet size and block size used to transfer data.We propose heuristics for tree construction which take link serialization into account. We evaluate this effect using simulations and experiments on the Planet- Lab network and show that using larger block sizes to transfer data can reduce the average finish time of the nodes in the multicast tree at the expense of slightly increased variance.