Extract the outer points of a Point Shape into a Line Shape?

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I've installed QGIS 2.8.2 since a few days and have no experience with this application. I try to extract the outer points of a Point Shape into a Line Shape, like a shell for the inner points. All points of the shape has to be in or on the border of the line.

Is there any possibility or function in QGIS, to do this ? (see figure 1 below)

Thanks for your help, Grimey

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