SIP/2.0 100 Trying
From: <sip:20@152.66.244.20>
To: <sip:10@152.66.244.10>
Via: SIP/2.0/UDP 152.66.244.20
Contact: <sip:10@152.66.244.10>
Call-ID: 6585CF47-7D22-4302-AD1D-E3F1BCC0E584
CSeq: 1 INVITE
Content-Type: application/sdp
Content-Length: 0
User-Agent: EXAMPLE UserAgent1.0