    OPTIONS sip:user@example.com SIP/2.0
Via: SIP/2.0/UDP host5.example.net;branch=z9hG4bK293423
To: sip:user@example.com
From: sip:other@example.net;tag=3923942
Call-ID: mcl01.fhn2323orihawfdoa3o4r52o3irsdf
CSeq: 15932 OPTIONS
Content-Length: 13
Max-Forwards: 60
Content-Length: 5
Content-Type: text/plain
