There is a growing interest of using Ethernet to support time constrained communication raised from process control, factory automation and other real-time applications. This paper first presents a comprehensive analysis of the temporal characteristics of traditional Ethernet and the improvements for them, then summarizes the interesting features offered by a switched Ethernet for supporting time constrained communication. At last, this paper points that it still lacks of general means to handle capability of switched Ethernet after investigating QoS (Quality of Service) of switched Ethernet.