P2P in this case probably means you would need an external server that handles the connection forwarding, that can be accessed by both camera and client.
A short pseudo-example of how i would imagine it has to work:
- Camera will be connecting to the proxy server to open the connection (since server cannot open the connection to the camera without port forwarding). Camera would also tell the proxy the unique ID which client needs to know for the connection.
- Client will be connecting to the proxy server, telling the unique ID it wants to connect to, and the proxy server connects the client to the existing camera connection.
- If the connection cannot be used, the proxy server must be able use something to get through the NAT, for example
UDP hole punching
Alternatively the camera would have to send the images to the server and client would then request them from the server, but i doubt you have the possibility to modify the camera to do this...
IMO all this for a single camera remote viewing is way too much work, either port forwarding or using a VPN would be the best solution.