%% You should probably cite draft-ietf-sip-199 instead of this I-D.
@techreport{holmberg-sipping-199-04,
    number =    {draft-holmberg-sipping-199-04},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-holmberg-sipping-199/04/},
    author =    {Christer Holmberg},
    title =     {{Response Code for Indication of Terminated Dialog}},
    pagetotal = 9,
    year =      2008,
    month =     feb,
    day =       21,
    abstract =  {This specification defines a new SIP response code, 199 Early Dialog Terminated, which a SIP entity can use to indicate upstream that an early dialog has been terminated. The response code can be used by a SIP entity, normally a forking SIP proxy, to allow the UAC to know that an early dialog has been terminated before it a final response is sent to the request.},
}