IP Cam keeps disconnecting [SOLVED]

I have several IP cams, including some of the popular  Amcrest/Foscam FI8910Ws. They were working fine, till one day they were not. Power cycling brought them back online, but they dropped off after only an hour or two. I could not find any clues on the net as to what was happening. What was strange to me that this behavior was evident in more than one camera, so it most likely was not a single camera failure. There were reports of these cameras losing track of their MAC addresses, and a suggested fix. It did not help.

It occured to me that I had upgraded my internal wired network from 100Mb to gigabit. I took an old 10/100 ethernet switch and put it between the network and the camera, on the hope that no gigabit timing would make it through the old switch. Lo! (and also Behold!) the cameras are now all permanently back on line. My guess is that after a while, on a gigabit circuit, some timing event crashes the cameras’ network interface and they become unreachable.