Caught as follows:
(omit the TCP three-way handshake)
The OPTIONS RTSP://192.168.1.206:554/profile2/media. SMP RTSP/1.0
CSeq: 2
The user-agent: LibVLC/2.2.2 (LIVE555 Streaming Media v2016.02.09)

Why do the CSeq here is 2?