%% You should probably cite rfc6809 instead of this I-D.
@techreport{ietf-sipcore-proxy-feature-03,
    number =    {draft-ietf-sipcore-proxy-feature-03},
    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-sipcore-proxy-feature/03/},
    author =    {Christer Holmberg and Ivo Sedlacek and Hadriel Kaplan},
    title =     {{Mechanism to indicate support of features and capabilities in the Session Initiation Protocol (SIP)}},
    pagetotal = 18,
    year =      2012,
    month =     jun,
    day =       11,
    abstract =  {This specification creates a new IANA registry, "Feature Cap Registry", for registering "feature caps", which are used by SIP entities not represented by the URI of the Contact header field to indicate support of features and capabilities, where media feature tags cannot be used to indicate the support. This specification also defines a new SIP header field, Feature-Caps, to convey feature caps in SIP messages.},
}