In a saucepan over medium heat, combine the sugar, wine and, if desired, cinnamon and bring to a boil. Reduce the heat to medium-low and simmer, stirring occasionally, until the sugar dissolves and the wine has reduced slightly, about 4 minutes. Add the cranberries and, if desired, the zest. Simmer until the cranberries soften and the sauce thickens, 10 to 12 minutes. Remove from the heat; remove and discard the cinnamon and/or the zest, if using. Set aside to cool for at least several minutes and up to several hours. Serve warm or at room temperature.