SIP/2.0 200 OK
Via: SIP/2.0/UDP nm;branch=foo;received=224.245.4.16;rport=26810
From: <sip:nm@nm>;tag=root
To: <sip:nm2@nm2>;tag=as4eeb82dd
Call-ID: 50000
CSeq: 42 OPTIONS
User-Agent: PBX 
Allow: INVITE, ACK, CANCEL, OPTIONS, PRACK, UPDATE, BYE, REFER, SUBSCRIBE, NOTIFY
Supported: replaces,timer,in-band-dtmf,100rel
Contact: <sip:123.160.173.169>
Accept: application/sdp
Content-Length: 0