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Disruption effect on continuous playback of the base stream

The base stream is more prone to disruption because the entire subtree rooted at a departing client is disrupted. As depicted in Fig. 16, for the same environment, the probability that a client's base stream will not be disrupted goes down to 0.885 and 0.856, respectively. The probability that more than five clients need to be contacted increases to 0.0069 and 0.0205. However, note that the base stream is played back after being buffered for the period equal to the sum of playback delay and the patch length. We propose the shifted forwarding technique to protect the base stream from the glitch by using this cushion. Shifted forwarding is similar to interval caching proposed for efficient memory caching. We give an example below to illustrate the idea. Suppose the session starts at time 0, and the client $i$'s parent node departs at time $t$. Client $i$ re-joins the base tree at time $t+\delta$. Thus client $i$ and all its descendant clients in the base tree miss the video from time $t$ to $t+\delta$. A glitch will be observed. Using shifted forwarding, client $i$ will send a message to its parent client, asking it to forward the content starting at $t$ (instead of forwarding the current data at $t+\delta$). Since the base stream has a cushion equal to the sum of the playback delay and patch size, the glitch can be avoided if the cushion is larger than $\delta$. Usually the cushion (sum of playback delay and patch size, on the order of minutes) is much longer than the rejoining time (usually at the order of tens of seconds [13]), uninterrupted playback of the base stream can be achieved with high probability.
next up previous
Next: Threshold adjustment - balancing Up: Failure Recovery - Providing Previous: Disruption effect on the
Yang Guo 2003-03-27