Cameras going down on network

[dorlow 0]

It all started about 3 months ago. I'm not sure what changed on the network, but every few days, 50 out of the 56 cameras will just go blank and I think pretty much at the same time. If I pull up the camera in a web browser with an IP address, I get a pop-up saying "connection failed" except it still pulls up the vivotek page and all the options are there to make adjustments to the camera, just where thre should be video on the page, it's a black box and says "connecting..." in the corner. The only cameras that seem to stay up stable are the cameras that physically plug into the MDF where the server is at. Any cameras traversing a fiber backbone seems to have this problem.