Three techniques are employed to give PROFINET its speed boost to a 31.25 microsecond cycle time: fast forwarding, Dynamic Frame Packing, and fragmentation.
Every microsecond counts. When a PROFINET frame passes through an Ethernet switch in a linear topology, the switch examines the frame to see if it should forward it or use it. So we moved the ID closer to the beginning of the frame. Now it can examine it sooner and know what to do with it sooner.
Dynamic Frame Packing
What if I could drop off a message for device 1 and not have it stay in the traveling PROFINET frame? That’s what Dynamic Frame Packing does. It’s like a delivery truck. The truck drops off a package at my office and its load is a little lighter as it drives to the next stop.
Unlike fragmentation of a disk drive, this fragmentation is good fragmentation! A full size Ethernet Frame will take 125 microseconds on a 100Mbit/sec network. If we did not fragment, we could not achieve 31.25 microseconds. So fragmentation is just chopping up Ethernet frames at the beginning of a string of PROFINET devices and reassembling them at the end.
All this to benefit the one percent of the market that needs it. Why is it that the one percent always gets special treatment? But at least with PROFINET the 99 percent are not penalized. (But we still want you to occupy PROFINET.)
Here is an animated presentation of Fast Forwarding, Dynamic Frame Packing, and Fragmentation:
More news from Hanover Fair is still to come.