%% You should probably cite rfc3398 instead of this I-D.
@techreport{ietf-sipping-isup-06,
    number =    {draft-ietf-sipping-isup-06},
    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-sipping-isup/06/},
    author =    {Jon Peterson and Gonzalo Camarillo and Adam Roach and Lyndon Ong},
    title =     {{Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping}},
    pagetotal = 68,
    year =      2002,
    month =     aug,
    day =       26,
    abstract =  {This document describes a way to perform the mapping between two signaling protocols: the Session Initiation Protocol (SIP) and the ISDN User Part (ISUP) of SS7. This mechanism might be implemented when using SIP in an environment where part of the call involves interworking with the Public Switched Telephone Network (PSTN).},
}