Session Initiation Protocol
    Request-Line: INVITE sip:5001@sip.softiphone.net SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 192.168.1.100;branch=z9hG4bK52ffa6c1cda5b285
        From: "5003" <sip:5003@sip.softiphone.net>;tag=81ee9e99dc30cc34
            SIP Display info: "5003"
            SIP from address: sip:5003@sip.softiphone.net
            SIP tag: 81ee9e99dc30cc34
        To: <sip:5001@sip.softiphone.net>
            SIP to address: sip:5001@sip.softiphone.net
        Contact: <sip:5003@192.168.1.100>
        Supported: replaces, timer
        Call-ID: b2d776f6e99851a4@192.168.1.100
        CSeq: 44559 INVITE
        User-Agent: Grandstream GXP2000 1.0.1.9
        Max-Forwards: 70
        Allow: INVITE,ACK,CANCEL,BYE,NOTIFY,REFER,OPTIONS,INFO,SUBSCRIBE,UPDATE,PRACK
        Content-Type: application/sdp
        Content-Length: 310
    Message body
        Session Description Protocol
            Session Description Protocol Version (v): 0
            Owner/Creator, Session Id (o): 5003 8000 8000 IN IP4 192.168.1.100
            Session Name (s): SIP Call
            Connection Information (c): IN IP4 192.168.1.100
            Time Description, active time (t): 0 0
            Media Description, name and address (m): audio 5004 RTP/AVP 0 8 18 3 4 101
            Media Attribute (a): sendrecv
            Media Attribute (a): rtpmap:0 PCMU/8000
            Media Attribute (a): rtpmap:8 PCMA/8000
            Media Attribute (a): rtpmap:18 G729/8000
            Media Attribute (a): rtpmap:3 GSM/8000
            Media Attribute (a): rtpmap:4 G723/8000
            Media Attribute (a): ptime:20
            Media Attribute (a): rtpmap:101 telephone-event/8000
            Media Attribute (a): fmtp:101 0-11