%% You should probably cite rfc3515 instead of this I-D.
@techreport{ietf-sip-refer-07,
    number =    {draft-ietf-sip-refer-07},
    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-refer/07/},
    author =    {Robert Sparks},
    title =     {{The Session Initiation Protocol (SIP) Refer Method}},
    pagetotal = 23,
    year =      2002,
    month =     dec,
    day =       4,
    abstract =  {This document defines the REFER method. This Session Initiation Protocol (SIP) extension requests that the recipient REFER to a resource provided in the request. It provides a mechanism allowing the party sending the REFER to be notified of the outcome of the referenced request. This can be used to enable many applications, including call transfer. In addition to the REFER method, this document defines the refer event package and the Refer-To request header. {[}STANDARDS-TRACK{]}},
}