The Use of Packet-Switched vs. Circuit-Switched Networks for Data Transport in a Public Transit Environment

Ethernet has become the de-facto standard for providing data transport not just throughout the internet but for numerous private and industrial networks. Prior to Ethernet’s dominance, circuit-switched networks (or time-division multiplexed networks like SONET) were popular choices for applications that required flexible and reliable data transport. Over the past 10 years, packet-switched networks in general (and Ethernet in particular) have usurped the role formerly played by these circuit-switched networks but is this a good development given that not all applications that require data transport are created equal? In the public transit environment, data transport networks are often used for mission critical applications that directly support revenue service such as signaling and train control and are increasingly based upon packet-switched networks. This paper will explore the current trend of using packet-switched as opposed to circuit-switched networks in the context of providing data transport for rail-based public transit agencies and, after examining five case studies, draw conclusions that are relevant for public transit agencies.