Ethernet was commercially introduced in 1980 and standardized in 1985 as IEEE 802.3. Due to the instability and unreliability of the initial introduction, safety critical systems have been slow to adapt Ethernet technologies. It is only until the Information Age brought on by the globalization of Internet in the 1990s that network gears become more cost effective, reliable, and technically suitable. With many Ethernet technologies to pick from, selection of a suitable network topology can be challenging. This paper offers insight on the problem of the optimum choice of an Ethernet technology for the purpose of safety critical system. Example of a typical CBTC system will be given along with the key design parameters and several Ethernet technologies analyzed. Simulation models are built on the basis of the two most common Ethernet technologies to provide means of comparison, and numerical results are presented in the paper.