[OpenSER-Users] CANCEL generated by openser after SIP/SDP Status: 200 OK

Hello, I have problems calling from my phones connected to openser to grandstream phones on another university to ser. Problem is, that my openser generates a "CANCEL" SIP packet sent to grandstream phone, but no CANCEL received from my phone. Wireshark shows something like this: 1189587144.843962 158.195.15.100 -> 158.197.16.77 SIP/SDP Status: 200 OK, with session description 1189587144.845528 158.197.16.77 -> 158.195.15.100 SIP Request: CANCEL sip:+421xxxx44903@domain.sk 1189587144.853654 158.195.15.100 -> 158.197.16.77 SIP Status: 200 canceling Communication before is OK. 158.197.16.77 is my openser server and 158.195.15.100 is peers phone. Any idea, why openser can generate this packet? Can openser generate a SIP packet not received from client? Calling from my phone to another phone on same university works well. Thank you. SAL