Why use a public address?

When an access client, such as XProtect Smart Client, connects to a surveillance system, an amount of initial data communication, including the exchange of contact addresses, is shared in the background. This happens automatically, and is completely transparent to the users.

Clients may connect from the local network as well as from the Internet, and in both cases the surveillance system must provide suitable addresses so the clients can get access to live and recorded video from the recording servers:

When clients connect locally, the surveillance system should reply with local addresses and port numbers.
When clients connect from the Internet, the surveillance system should reply with the recording server's public address. This is the address of the firewall or NAT (Network Address Translation) router, and often also a different port number. The address and the port can then be forwarded to the server's local address and port.
To provide access to the surveillance system from outside a NAT (Network Address Translation) firewall, you can use public addresses and port forwarding. This allows clients from outside the firewall to connect to recording servers without using VPN (Virtual Private Network). Each recording server can be mapped to a specific port and the port can be forwarded through the firewall to the server's internal address.