@banosr While sure you can send your camera feeds over the wire to some other site.. But 20 feeds with constant record is going to add up to some bandwidth.. Depending on what resolution your recording.
But If I call up the 3 feeds all at once, in 4k mode and only at 15fps.. Maybe your only like 720 and the streams use much less bandwidth?
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Lets call it 10Mbps each, time 20 cameras - your looking at 200Mbps.. That is over half of your site 2 bandwidth.. Is that something you want to do?
And then site 3 15 would be 150mbps that is like 1/2 of your upload there..
Now your main site would have 350 coming in.. Like half of your 750mbps..
I would want the NVRs to be local to where the cameras are - and sure if you want to view a feed or keep an eye on them and display the video, but at a lower res, etc. at your site 1..
I mean it can be done sure - but I don't think I would do it.. Also so what if your connection is down, now you have no video of what went on..
I would put in NVRs at the site(s) where the cameras actually exist to be honest.