In Part One of this series, we discussed how PROFINET leverages IT protocols such as Simple Network Management Protocol (SNMP), File Transfer Protocol (FTP) and Hyper Text Transfer Protocol (HTTP) to provide easy configuration and diagnostics over the network. Now in part two, we’ll cover PROFINET device naming, PROFINET Discovery and Configuration Protocol (DCP), and Link Layer Discovery Protocol (LLDP). Finally, in part 3 we’ll cover PROFINET application protocol features. All of these features show the ‘simple’ side of network management and ease of network troubleshooting when using PROFINET to make it the best and most comprehensive industrial protocol suite around.
A distinctive feature of PROFINET is that all devices are configured with device names in the engineering tool and then the name is assigned to the device by using Discovery and Configuration Protocol (DCP). Using a name makes it much easier to manage the devices on the system and really it’s nothing new. Information Technology (IT) actually has used device names on computers and printers and network devices for years so they can be accessed when using Domain Name Services (DNS) instead of always trying to remember the Internet Protocol (IP) address. What was the IP address of the email server again please, the printer, etc.?
It really makes it easier when using descriptive device names such as “Filler-panel2”. Now we have a device name, location, and could even put more details into the name for easy device recognition. One might say that it is more to remember (you can also just shorten the name), but that’s where the PROFINET function ‘DCP identify all’ comes in and you can simply browse the network to find all of the available devices and get their related information (name, current IP Address, manufacturer info, and other info) at any time. The PROFINET IO controller (PLC) also uses DCP to automatically set the IP address on the devices at startup, making the device setup and startup process much faster.
LLDP is supported by default in all PROFINET devices. With LLDP, devices send a special “Hi neighbor” message out of each switch port on the device every few seconds to their neighbor stations. The message includes the device name, address info, port info, and more. This information gets stored and can be read out anytime with acyclic PROFINET read requests (mandatory) or optionally through standard SNMP (if supported) per our previous article. An advantage of this information being stored in the devices is that we can read the network topology and determine the health of the expected connections as well as network statistics like bandwidth utilization. This helps us quickly isolate and diagnose network faults. In conjunction with DCP, this gives us the ability to set station names automatically if needed via the PROFINET IO Controller.
DCP and LLDP also enable the use of “simple device replacement” without any engineering tools if desired for worry-free maintenance in case of a device failure and replacement. With this, an IO Controller can automatically set the names, if needed, upon initial power up or replacement device connections. Simple commissioning can thereby be achieved for quick and easy plant start up.
To describe how this works in layman’s terms, let’s say we had a device fail named “IO3” in our facility and we get a new one out of the box from the tool crib. The new device is going to come out of the box with an empty name and new Ethernet MAC address per the PROFINET standard. After connecting the device to the network the PROFINET IO controller can’t find “IO3”. However, in a few seconds, the neighboring station will send the new device an LLDP message. Again, let’s say the neighbor device is named “Switch” and the cable is connected to “Port 4”. So, the new device will then get what’s called an LLDP alias name (since it doesn’t have a valid name yet.) of “Switch.P4”. Now the IO controller can also try to find the device via the LLDP Alias name as another try. Once found the device is then issued its actual name “IO3”, the startup process completes and the device comes back online. Now that’s simple! No extra tools or configuration steps were needed for the replacement device.
Let’s step through that process:
In conclusion, PROFINET has the most collective and comprehensive diagnostics suite available of any Industrial Ethernet protocol and its focus is to be simple. This helps make it easy to manage your network, implement diagnostics in your applications, and keep downtime to a minimum.
We’ll cover more about the PROFINET application diagnostic side of things in part 3 of this series.
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