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.
[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.]
–Carl Henning
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