SIP/2.0 200 OK
From: <sip:nm@nm>;tag=root
To: <sip:nm2@nm2>;tag=6ebaa9da-c4388a3f50340-b50e79a8-6564a8c0-0500046
Call-ID: 50000
CSeq: 42 OPTIONS
Via: SIP/2.0/UDP nm;received=224.97.81.197;rport=26810;branch=foo
Allow-Events: message-summary, dialog, presence
Accept-Language: en
Accept: application/sdp
User-Agent: MATRIX SARVAM UCS SOHO V1R6.5.0
Supported: replaces
Allow: INVITE,ACK,CANCEL,BYE,REFER,SUBSCRIBE,NOTIFY,PUBLISH,MESSAGE,OPTIONS,UPDATE,INFO
Content-Length: 0

HTTP/1.1 401 Unauthorized
Connection: Keep-Alive
WWW-Authenticate: Digest realm="HuaweiHomeGateway",nonce="fc89df074640da9a2c192638708edb12", qop="auth", algorithm="MD5"
Content-Length: 0