%% You should probably cite draft-ietf-sipcore-content-id instead of this I-D.
@techreport{holmberg-sipcore-content-id-00,
    number =    {draft-holmberg-sipcore-content-id-00},
    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-sipcore-content-id/00/},
    author =    {Christer Holmberg and Ivo Sedlacek},
    title =     {{Content ID header field in Session Initiation Protocol (SIP)}},
    pagetotal = 8,
    year =      2016,
    month =     aug,
    day =       16,
    abstract =  {This document specifies the Content-ID header field for usage in the Session Initiation Protocol (SIP).},
}