More on Network Topology

September 4, 2019

Since PROFINET is based on standard unmodified Ethernet, it gives users all topology options: cabled topologies and wireless connections(via Bluetooth or Wi-Fi). The table below summarizes the benefits and challenges of different PROFINET topology configurations.

Topology Description Benefits Challenges
Line Most PROFINET devices have at least two ports, with such ports being part of a built-in switch in the device. Built-in switches allow users to connect devices in a line topology without external switches.
  • Built-in switches in PROFINET devices are usually available. External switches are optional.
  • Fewer cables needed
  • If a node in the line fails, downstream nodes lose communication.
  • User must account for line depth limitations[1].
Star and Tree Built-in or standalone switches allow for star/tree topologies.
  • Efficient topology for multiple nodes nearby
  • If a central switch fails, communications to all connected nodes will be affected.
  • Additional cables and external switches
Ring PROFINET allows you to implement a ring topology by managing it with two defined media redundancy protocols: Media Redundancy Protocol (MRP)[2] and Media Redundancy for Planned Duplication (MRPD)[3].
  • Media Redundancy: In case of a failed cable or node within the ring, operations may continue.
  • Devices in the ring must support PROFINET media redundancy.
  • Additional cabling
  • Additional configuration of the devices that make up the ring.
Wireless Wi-Fi or Bluetooth can become part of a PROFINET network backbone.
  • No need for cables or additional hardware
  • Limited speed and determinism
  • Installation requires in-depth analysis of the wireless conditions (interference, signal decay, etc.)

Footnotes

[1] Each switch that is placed between a device and its controller introduces a delay in the data transfer. The number of switches between a controller and a device is called the line depth. A large line depth will add delay, which must be considered when planning the network topology.

[2], [3] MRP and MRPD enable the connection of devices based on ring topologies.

MRP: If the transmission link in the ring is interrupted, the ring manager immediately activates the alternative communication path. The recovery time is in the millisecond range.

MRPD: Each sender in the ring sends two equal frames to the receiver in opposite directions around the ring. In case of a network failure, one frame will still arrive at the receiver. MRPD ensures non-stop connectivity with a recovery time of zero.

Read the full Topology White Paper HERE:

Industrial Topology Options and PROFINET

-Nelly Ayllon