[Osip] [osip] Doubt regarding the messages sent by the callee in response to the Invite message

[prashant jain]

Hello

I have written a test application using eXosip2 library, to check the basic
call set up mechanism between two client. Following is the flow of messages
transferred between caller and callee in sequence:

1. CALLER snd a invite to CALLEE
2. CALLER rcv 100 trying from CALLEE
3. CALLER rcv 101 dialog establishment from CALLEE
4. CALLER rcv 180 ringing from CALLEE
5. CALLER rcv 200 ok from CALLEE
5. CALLEE rcv ack from CALLER

I am using stateless proxy registrar to register both of my client to make
the call. My point of concern is according to RFC3261 100 trying messages
are sent by the proxy to the caller not by the callee, callee simply send
180 ringing once it received the invite and after SDP confirmation it will
send 200 ok.  Than why I am getting 100 trying from callee, do I missing
some basic thing in this conversation.

Thanks and Regards
Amit