PROFINET can use a Best Buy Ethernet Switch, really? Yes, really.
At the Atlanta PROFINET one-day training class one of the attendees thought I was being “disingenuous” claiming that PROFINET can use an Ethernet switch from Best Buy. (I thought he meant I was lying, but the dictionary says that disingenuous is “lacking in candor; also, giving a false appearance of simple frankness.”) Nothing false here. But I did go to BestBuy.com to see if they really did carry Ethernet switches that could be used in a PROFINET application. The first one in the search results for “Ethernet switch” was “D-Link – Green Ethernet 5-Port 10/100/1000 Gigabit Ethernet Switch” for $34.99. It meets the minimum requirement for PROFINET use: it’s 100Mbit full duplex. Yes, that’s the only requirement. This switch also includes an optional feature we recommend: Quality of Service (QoS). This feature just allows Ethernet frames with higher priority to be sent first. Ethernet frames containing PROFINET real-time data have a higher priority than TCP/IP frames. Now this is an unmanaged switch meaning its only diagnostic feature is LEDs.
Just because you can use an unmanaged switch doesn’t mean you should use an unmanaged switch though. But I already ranted about that in “Switch Education.”
[Now to be fair, if I were using a switch between drives to carry motion control traffic, I would need a more expensive switch, but such usage is rare for two reasons. One, most PROFINET drives have built-in switches. Two, motion control applications are not that common compared to standard IO applications.]