U <IP>:5060 -> <IP>:5060
INVITE sip:123456789@outbound.example.com SIP/2.0.
Record-Route: <sip:<IP>;ftag=A46BD3D8-1E92;lr=on>.
Via: SIP/2.0/UDP <IP>;branch=z9hG4bK81bc.ea8154e6.0.
Via: SIP/2.0/UDP  <IP>:5060.
From: "anonymous" <sip:<IP>>;tag=A46BD3D8-1E92.
To: <sip:123456789@n.e164.org.uk>.
Date: Thu, 21 Jun 2007 13:38:23 gmt.
Call-ID: 83D50DC1-1F3311DC-B3ABB8FE-F56123F3@<IP>.
Supported: timer.
Min-SE:  1800.
User-Agent: MSSGW.
Allow: INVITE, BYE, CANCEL, ACK.
CSeq: 101 INVITE.
Max-Forwards: 14.
Remote-Party-ID: <sip:<IP>>;party=calling;screen=yes;privacy=full.
Timestamp: 1182433103.
Contact: <sip:<IP>:5060>.
Expires: 180.
Allow-Events: telephone-event.
Content-Type: application/sdp.
Content-Length: 404.