SIP/2.0 407 Proxy Authentication Required
Via: SIP/2.0/UDP nm;branch=foo;rport=26810;received=224.125.198.107
From: <sip:nm@nm>;tag=root
To: <sip:nm2@nm2>;tag=0fa172362cbd230ae60bf4daec3ebf61.1e840000
Call-ID: 50000
CSeq: 42 OPTIONS
Proxy-Authenticate: Digest realm="nm", nonce="Zgc1pWYHNHnqpiVU1UGGPDtIBKnxxQSA"
Server: VoipXpress Proxy 5.4.2
Content-Length: 0
