The ability for VMS to work during a network outage depends on the scope of the outage.
If the internet or WAN connectivity goes down, the VMS system can continue processing video images on the NVRs and store the processed videos locally. When the Internet connectivity is restored, the processed videos can be uploaded to the cloud application for remote access to the video management software.
If there is a LAN outage, smart cameras can continue to record videos and upload them to the cloud when connectivity is restored. However, analog cameras and IP cameras may not remain functional.