When an RTSP camera works 95% of the time and falls apart at the worst possible moment, you usually don't have a network problem — you have a session problem. Here is the checklist I run before I touch the camera config or the VMS.
1. Confirm the session actually opens
The first thing to check is whether DESCRIBE returns a valid SDP. If the server replies with a 401 before SDP, your credential realm is wrong; if it returns SDP with m=video 0, the server is advertising a track it cannot actually serve. Don't proceed until DESCRIBE returns something usable.
2. Read the SDP like a packet, not a string
Two things matter most:
