When we first started selling Milesight their NVRs could manage 3rd-party cameras that were on your network, but the Milesight NVRs could not provide PoE power to 3rd-party cameras. Now though, with the most recent NVR firmware update*, the NVRs will provide power but to get it to work is a...
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So you need to connect the Milesight camera(s) to your local network via a PoE injector/switch and using Milesight's Smart Tools you need to change the Milesight camera IP address and gateway address to match the subnet range of the Hikvision NVR (e.g. IP address 192.168.254.2/3/4/etc... [whichever channel is available] and Gateway 192.168.254.1) and once these details are set you can then connect the camera to the PoE ports on the NVR, make sure that the corresponding channel in the camera menu is set to manual, enter the details you just set the camera to and enter the password.
Once these details are saved the camera should be connected, but directly connecting 3rd-party cameras to a Hikvision NVR can limit your access to camera-specific features and settings, so we usually recommend that users add 3rd-party cameras to the NVR over their local network by activating each camera with its own local network IP address and manually adding as described above.