Scalable network intelligence
Lütze Transportation GmbH presents a new and innovative family of Ethernet switches that can cover all complexity and hierarchy levels on rail vehicles and combines key factors of size, durability, price and flexibility in one.
Ethernet as a communication bus in rail vehicles – has now become a reality
It is now a reality! Ethernet is now used in rail vehicles across the globe, initially in the passenger information and infotainment level and now at the control level. According to the definition of Train Communication Network (TCN) in the standards IEC61375-2-5 and IEC61375-3-4, the so-called Ethernet Train Backbone (ETB) replaces the soon-to-be-obsolete train bus WTB and the Ethernet Consist Network replaces the previous MVB or CAN field bus networks. The communication protocol between the bus participants is implemented with the Train Real Time Data Protocol (TRDP). This network protocol is IP-based and, thanks to the new structure, allows direct communication between all network participants. However, this development goes hand-in-hand with a fundamental paradigm shift: a new network topology.
What are the special features of the new topology?
Managed Ethernet switches are required for implementation; these not only need to satisfy the feature set known in industrial automation, but also requirements from the rail industry.
Bus participants (End Devices [ED]) are connected to the ECN via managed Ethernet switches (Consist Switches [CS]) within a train segment to secure the communication between all participants, for instance, control units or decentral I/O nodes. The topology within an Ethernet Consist Network is not specified by any specific standard, typically ring topologies are used. Due to the fact that a train can have several train segments (ECNs), these are also connected via the cross-vehicle ETB by means of intelligent Layer-3 switches.
How can individual shielded vehicle segments (ECN) communicate with other segments?
Using a network address translation (NAT) function, the network participants of the Consist are invisible to the outside. This is achieved by masking incoming IP addresses and translating them internally. This is how data from the vehicle (ETB) with the IP address 10.10.1.0 and 255.255.255.0 arrives; the NAT router translates this into a local IP address, e.g. 192.168.10.0/ 255.255.255.0, that is assigned to a vehicle control unit. As soon as the processed data is available in the control unit, it is sent to the NAT router. The router translates the network address of the control unit and sends the data with the IP address 10.10.1.0 to the counter-point, e.g. decentral I/O nodes.
As a result of the continuous translation of the IP addresses, the ECN network participants become invisible for participants outside the ECN. Consequently, outside third parties cannot access the control level of the vehicle.
The address translation function has positive secondary effects on the availability and configuration of IP addresses. In a multi-section vehicle with duplicated ECNs, network configurations need to be made manually without a 1:1 NAT. This is time-consuming and cost-intensive. If all networks are managed centrally, steps must be taken to ensure that the IP addresses have only been issued once. Networking and user-friendliness are important criteria for cost-effective installation when configuring the network.
What requirement profile does an Ethernet switch for rail vehicles need to meet?
An Ethernet switch that is to be installed in a rail vehicle network needs to fulfil the requirements from the EN50155 norm, demonstrating durability in harsh environments.
An important characteristic of an Ethernet switch is excellent reliability. Unscheduled maintenance work and poor availability can become very expensive for the train operator.
If individual network segments fail due to defects, it is important to keep the network operational via a redundant path, e.g. via ring redundancies such as RSTP (Rapid Spanning Tree Protocol).
The design, integration and maintenance of Ethernet-based networks must be carried out quickly, securely and reliably. During the commissioning phase or scheduled maintenance work, it is important that the configuration can be made without the need for any special software; ideally it should be possible to clone a configuration from one device to the other.
A firewall can screen and protect the network from external influences, such as unintentional installation mistakes and any resulting connection to the infotainment level which could initiate criminal attacks e.g. cyber attacks. It is essential that the control level in the vehicle is shielded.