Glossary · Industrial communication
Bus topology
Also known as: Bus network, Multidrop topology
German: Bustopologie
In industrial communication, a bus topology is a network structure in which all nodes are connected to one shared transmission line. Only one node can transmit at a time, so access is controlled by the protocol, for example by master polling, token passing or arbitration.
- Industrial communication
In one sentence
A bus topology connects all nodes to one shared line; the protocol controls which node may transmit at any moment.
Example
A PROFIBUS DP segment runs as a single RS-485 bus from the PLC along ten drives, with an active terminating resistor at both ends.
How it applies
- Engineering: Classic fieldbuses such as PROFIBUS, CAN bus and Modbus RTU use a bus topology. Designers observe the maximum segment length, the number of nodes per segment, stub line limits and termination at both ends.
- Commissioning: Missing or doubled terminating resistors cause reflections and sporadic errors that are hard to find. Bus analyzers and oscilloscopes help to check signal quality.
- Maintenance: A short circuit on the shared line can take down the whole segment; a single removed device usually doesn't if it is connected via a stub or plug that keeps the bus closed.
- Documentation: The documentation team shows the bus layout in the network drawing, marks termination points and states the cable type and permissible lengths.
Bus topology vs. line topology
In a bus, all nodes share one passive medium. In a Line topology of industrial Ethernet, each device has two ports and forwards frames to the next one, so each link is a separate point-to-point connection. Both look similar in the drawing, but they fail differently.