;tag=[pid]SIPpTag00[call_number] To: Contact: Expires: 15 Call-ID: [call_id] CSeq: 1 REGISTER Content-Length: 0 ]]> ;tag=[pid]SIPpTag00[call_number] To: Contact: Expires: 15 [authentication] Call-ID: [call_id] CSeq: 2 REGISTER Content-Length: 0 ]]>