[Sip-implementors] Question regarding Sending CANCEL

[Ravishankar]

Hi,   I have a question about sending CANCEL message.   The situation is like this.   UserA sends an INVITE to UserB through proxy. UserA Sends a CANCEL before receiving any response to the INVITE sent.   Is it valid to send a CANCEL before receiving any response for an INVITE. Should UserA wait for either a provisional response or final response before deciding to send a CANCEL or BYE Should UserA keep retransmitting the INVITE till it receives a response and then send either CANCEL or BYE.   I would appreciate if someone can clarify this for me.   Thanks   Ravi