SIP/2.0 200 OK
Via: SIP/2.0/UDP nm;rport=26810;received=224.44.109.174;branch=foo
Call-ID: 50000
From: <sip:nm@nm>;tag=root
To: <sip:nm2@nm2>;tag=foo
CSeq: 42 OPTIONS
Allow: PRACK, INVITE, ACK, BYE, CANCEL, UPDATE, SUBSCRIBE, NOTIFY, REFER, OPTIONS
Accept: application/sdp, application/simple-message-summary, message/sipfrag;version=2.0
Supported: replaces, 100rel, timer, norefersub
Allow-Events: message-summary, refer
User-Agent: TP-Link SIP Stack V1.0.0
Content-Length:  0