单项选择题 Jitter is an unwanted variation of one or more characteristics of a periodic signal in electronics and telecommunications and（）refers to call issues that cause variations in timing or time of arrival.

单项选择题 Which VPN management feature would be considered to ensure that the network had the least disruption of service when making topology changes?（）

多项选择题 Which two of these are correct regarding the recommended practice for distribution layer design based on the following configuration?（）