A data communication system (DCS) for railway applications provides both ground-based and onboard applications with a solution for exchanging information where and when it’s needed, irrespective of the position of the train. The usual DCS architecture for railway applications is an integrated Ethernet-IP network that includes a wired backbone network, wireless wayside network, and onboard network, with the onboard network handling communications between all communication-based train controller (CBTC) sub-systems. A CBTC must be protected by a robust security system, and requires continuous communication in circumstances where roaming is an unavoidable reality and occurs at very high speeds. For this reason, railway operators have been on the lookout for products that guarantee near-zero handoff latency between train and ground. Moxa’s Turbo Roaming can keep the roaming “break-time” under 50 ms at high speeds ensures uninterrupted connections for transmitting critical data, such as real-time voice and video streams. The CBTC is performed by the non-vital Automatic Train Operation (ATO) components under the supervision of the vital Automatic Train Protection (ATP) components. Therefore, security is very critical for DCS to authenticate all communication between subsystems.
To allow seamless roaming for high-speed trains, Moxa’s rail-specific Turbo Roaming technology is enabled by a Wireless Access Controller (WAC) that offers centralized security management. When roaming to another AP, the client can be pre-authenticated by the WAC to bypass the re-authentication process, which reduces the switch-over time to 50 ms. High-standard security with WPA, WPA2, and 802.11i is provided to ensure secure network access.
Deployed at the OCC, each WAC-1001 can manage up to 200 APs on the same LAN. For larger-scale WLANs, inter-controller roaming can be used to support hundreds of APs. When a client roams from one WAC’s zone to another, the two controllers exchange security keys and the new controller copies the security key to the new AP. The client can thus continue to roam between APs at under 50 ms, while still maintaining network security.
On a WLAN, adjacent APs should work through different channels to avoid radio interference. Moxa provides three non-overlapping channels for roaming to avoid adjacent channel and co-channel interference.
A CBTC relies heavily on the WLAN to support continuous train-to-ground communications, and the safe way to avoid link failure on a WLAN is through redundancy. Moxa offers multi-redundancy technology that includes wireless redundancy using dual-RF design, Ethernet redundancy using RSTP, and power redundancy using dual DC inputs and PoE, which sufficiently guarantees secure transmissions for video, voice, and other demanding applications such as real-time PIS systems.