@misc{rfc7433,
    series =    {Request for Comments},
    number =    7433,
    howpublished =  {RFC 7433},
    publisher = {RFC Editor},
    doi =       {10.17487/RFC7433},
    url =       {https://www.rfc-editor.org/info/rfc7433},
    author =    {Alan Johnston and James Rafferty},
    title =     {{A Mechanism for Transporting User-to-User Call Control Information in SIP}},
    pagetotal = 19,
    year =      2015,
    month =     jan,
    abstract =  {There is a class of applications that benefit from using SIP to exchange User-to-User Information (UUI) data during session establishment. This information, known as call control UUI data, is a small piece of data inserted by an application initiating the session and utilized by an application accepting the session. The syntax and semantics for the UUI data used by a specific application are defined by a UUI package. This UUI data is opaque to SIP and its function is unrelated to any basic SIP function. This document defines a new SIP header field, User-to-User, to transport UUI data, along with an extension mechanism.},
}