%% You should probably cite draft-ietf-sipcore-199 instead of this I-D.
@techreport{ietf-sip-199-08,
    number =    {draft-ietf-sip-199-08},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-ietf-sip-199/08/},
    author =    {Christer Holmberg},
    title =     {{Response Code for Indication of Terminated Dialog}},
    pagetotal = 16,
    year =      2009,
    month =     apr,
    day =       9,
    abstract =  {This specification defines a new SIP response code, 199 Early Dialog Terminated, which a SIP forking proxy and a UAS can use to indicate upstream towards the UAC that an early dialog has been terminated, before a final response is sent towards the UAC.},
}