OPTIONS sip:user@example.com SIP/2.0
To: sip:user@example.com
From: sip:caller@example.net;tag=3ghsd41
Call-ID: zeromf.jfasdlfnm2o2l43r5u0asdfas
CSeq: 39234321 OPTIONS
Via: SIP/2.0/UDP host1.example.com;branch=z9hG4bKkdjuw2349i
Max-Forwards: 0
Content-Length: 0
