Network Design for the Digitalized Public Transport Bus
17 Nov, 2021

Optimizing the planning and deployment of vehicles begins with the availability of live data between the control center and the vehicle fleet. In short, digitization starts with the network design in the vehicles. This should meet the requirements of the transport operators. On the one hand, to ensure a high quality of service for passengers, and on the other hand, to optimize the effectiveness of internal operations.

In the following, we design step by step an IP network for digitalized public transport buses that ensures a high level of data transparency and thus the best conditions for efficient public transport operations.

Selecting IP Components

In a typical case, all or nearly all existing devices in the vehicle are connected into a network. In this example, we equip a solo bus with all the devices we consider important for efficient operation and an optimal passenger experience. This includes interior and exterior displays, ticketing systems, passenger counting systems, digital cameras or recorders, and passenger Wi-Fi. In the network design, we also consider the on-board computer, which plays a central role in network control, and the router, which sends network data to the control center.

All devices are components that have their own IP addresses and can be accessed remotely. The device configuration itself is not covered here.

All onboard devices that are to be installed are summarized in a list:

  • Board computer x1
  • Driver control unit x1
  • Ticket validator x2
  • Passenger counting system x2
  • Camera x3
  • Video recorder x1
  • Travel indicator x3
  • Passenger information system x2
  • Router x1
  • Managed Fast Ethernet Switch x2

We decide on the type of switches we will use to build our network at the end. We choose managed switches because they provide the visibility and control we need for our digitalized city bus. We make the number of switches and the number of ports per switch primarily dependent on the total number of peripherals. At least one port per switch is left free for maintenance access to the entire network as well as for future network expansion.

>> Read also: How to Choose the Right Switch for Public Transport Vehicles


Installation Conditions

Taking into account the function that each device performs in the bus as well as the space available, we determine the exact installation location for each device. We arrange the devices schematically as they will later be installed in the vehicle.

ℹ The power supply for the IP devices is also important for the installation and network planning. Therefore, when determining the installation location of switches, the cable routing must also be considered. The same applies to retrofits where cables are already routed. Devices that are supplied via Power over Ethernet (PoE) do not require a separate power supply cable and are supplied directly by the switch. For this, the Ethernet switch used should support the PoE function.


Practice shows that line topologies are most practical in buses and therefore make the most sense. For our solo city bus, we also decide on a simple line topology, which we implement with two Ethernet switches. Both switches have PoE and Gigabit ports (for connection between both switches and switch router). Thanks to 16+10 ports, all intended devices can be connected, leaving ports for future network expansion.

ℹ Leaving ports free is a common practice and is also recommended by the Public Transport Interoperability Organization ITxPT.

Communication Plan

In a network with many participants, it is often not absolutely necessary or even desirable for all of them to be able to communicate with each other. To prevent this, a precise communication plan is necessary. It schematically shows which devices in the bus should communicate with each other and which should not. This also results in the logical network infrastructure.

ℹ A limited communication capability of the devices within the network is essential in complex, digital IP networks. Managed switches make this possible by dividing the entire network into logical subnetworks. This ensures, for example, that the passenger Wi-Fi is separated from the rest of the systems (e.g. camera). Thus, unwanted intrusions are prevented and the security level of the data is increased.

Network Settings

After defining the logical network infrastructure, we implement it schematically using virtual LANS (VLANs). The network separation can be seen in the figure below. Thus, cameras and VTRs exchange data with each other, but they do so only within the virtual video network. Only network-critical IP participants such as the on-board computer and the router have access to all data or forward it.

Note: Typically, not all devices in a network are VLAN-capable. If necessary, the managed Ethernet switch takes over the separation, whereby a fixed VLAN is assigned to the respective switch port. Thus, the connected subscriber can only communicate within this VLAN.

ℹ Under certain circumstances, the problem of logical network separation can also be solved by the router. In some cases, the passenger Wi-Fi can be connected to the router or is already integrated into it.

The detection of the individual devices in the network is done via individual IP addresses, which are to be assigned at this point.


Node IP address VLAN Member
Vehicle Communication Gateway Management, journey data, video, Wi-Fi, ticket
Switch 1 Management, journey data, video, Wi-Fi, ticket
Switch 2 Management, journey data, video, Wi-Fi, ticket
Destination sign 1 Journey data
Destination sign 2 Journey data
Destination sign 3 Journey data
Camera 1 Video
Camera 2 Video
Camera 3 Video
Camera 4 Video
Video recorder Video
Passenger info 1 Journey data
Passenger info 2 Journey data
MADT Journey data
Ticket validator 1 Ticket
Ticket validator 2 Ticket
Passenger counting system 1 Journey data
Passenger counting system 2 Journey data
Passenger Wi-Fi Wi-Fi
Maintenance access Management, journey data, video, Wi-Fi, ticket



To ensure the smooth functionality of the digital IP network on board our city bus, we include permanent network monitoring in the network design. In some cases, this is made possible via the on-board computer. Since the switch has a physical connection to each node in the network, diagnostics using a managed Ethernet switch is more effective.

Permanent monitoring makes sense for two main reasons:

  1. For troubleshooting
  2. Control over the running operation.

Managed Ethernet Switches can provide information about the network status using special protocols:

  • ITxPT Inventory Service x-status: Monitoring is event-based: If an undesired event occurs, a message is sent to all nodes using DNS. The fault can be forwarded directly to the control center via the router. This function is suitable for maintaining an overview of the entire vehicle fleet. It is essential, functionally relevant monitoring.
  • Remote logging: All events that are logged in the switch are also forwarded to a remote server in the control center. Extensive monitoring and initial diagnostics are possible here.
  • SNMP Trap: Error messages can be sent using the Simple Network Management Protocol.

Please check in advance which of these protocols your Ethernet switch supports.

Final Design

To get a working network design for our line bus, we finally determine how to configure the whole IP network. The first thing to do is to clarify what mechanisms are available to make settings in the vehicle. The classic case of manually configuring each individual device or switch can be very time-consuming with regard to an entire fleet. A simpler option for this is offered by ROQSTAR Ethernet switches from TRONTEQ. A new solution allows all switches in a predefined network to configure each other. In practice this means that the configuration has to be done only once per bus and not per device.

In any case, when thinking about configuration, the entire fleet must be considered and not just a single vehicle.

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Our products are fundamental for the digitalization in public transport. ROQSTAR M12 Ethernet Switches provide the network infrastructure for e-ticketing, passenger counting systems (PCS), dynamic passenger information (DPI) and closed-circuit television (CCTV).


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