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Burning Questions on Network Design

Last year we hosted a PROFINET Installation webinar. After an interactive Q&A section, we got several comments expressing interest in Network Design. This year we were able to put together an hour-long webinar on PROFINET Network Design. Due to time limitations, we were not able to answer all the questions that came in through the presentation, but we would like to answer them here:

Q&A

What is the difference between managed and unmanaged switches?

An unmanaged switch has no built-in intelligence except to send incoming Ethernet frames out the right port – the port that the destination device is connected to. Managed switches can offer several advantages, including user option selection based on a Command Line Interface (CLI) or Graphical User Interface (GUI), and provide diagnostics capabilities. Managed switches can also be PROFINET devices, with a respective General Station Description (GSD) file. With PROFINET it is truly your decision since you can use either a managed or an unmanaged Ethernet switch.

Does PROFINET require special switches?

With PROFINET there is no need for “special” Ethernet switches. The only requirement for Ethernet switches in a PROFINET network is 100 Mbps full duplex transmission. Most Commercial Off-The-Shelf (COTS) switches can work in a PROFINET network.

If there is a built-in switch in the device, what would it normally be? cut through or store and forward?

This is dependent on the device and the PROFINET conformance class.  Class A/B PROFINET RT devices could support a cut through switch as an option, but typically would be store and forward as this works fine for RT applications. Conformance class C, PROFINET IRT devices have a cut through switch built into the hardware to help avoid delays and minimize jitter for motion control applications.

How do you achieve media redundancy?

PROFINET allows you to create network media redundancy with a ring topology. Ethernet should never be connected in a ring without being managed. Packets may go in circles infinitely and many issues can arise. But, PROFINET offers a solution by managing a ring topology with two defined media redundancy classes: Media Redundancy Protocol (MRP) and Media Redundancy for Planned Duplication (MRPD) or ‘bumpless’ redundancy. The devices that make up the ring must be MRP or MRPD capable, respectively. More information here=> https://us.profinet.com/switches-and-ring-topology/

You mentioned MRP and MRPD, but what about HRP?

HiPER-Ring protocol (HRP) was a predecessor to MRP. HRP only considered the network components (switches) as part of the ring topology and not the devices or controllers.  With PROFINET MRP and MRPD, you can do a ring with controllers, devices, and switches.

Can devices have a slower update time (for example 50 ms)?

Yes, the update time can be set based on your application requirements.

Is there any limitation on cable lengths?

Yes, there are some cable length limitations. The limitations depend on the media type. As in standard Ethernet applications, the maximum distance between two endpoints of communication is 100 m when using copper cabling. For fiber optics cables, length limitations can vary. The table below shows typical transmission paths based on fiber classes.

Can you mix Ethernet/IP devices and PROFINET devices on the same network?

Yes, you can mix PROFINET with Ethernet/IP in the same network infrastructure. But, PROFINET devices will be communicating with PROFINET Controllers and Ethernet/IP devices with Ethernet/IP controllers. They may be able to share the cabling and general network infrastructure, but they won’t be able to communicate. Only a proxy or a gateway would allow devices from different protocols to communicate.

Is there any vision system available with the PROFINET standard?

Yes, there are actually many device manufacturers that have embedded PROFINET in their vision systems. To find these products, you can start searching in our Product Finder (https://www.profinet.com/products/product-finder/), but ultimately searching the web or your preferred vendor website may be your best bet.

Webinar Recording

We hope these answers shine some light into some common PROFINET network design questions. If you would like to follow up with further questions, feel free to contact us directly. Also, the complete webinar recording and slide deck are available for download HERE=>

PROFINET Network Design