%% You should probably cite draft-allen-sipping-poc-p-answer-state-header instead of this I-D.
@techreport{allen-sipping-poc-p-headers-01,
    number =    {draft-allen-sipping-poc-p-headers-01},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-allen-sipping-poc-p-headers/01/},
    author =    {Andrew Allen},
    title =     {{Private Header (P-Header) Extensions to the Session Initiation Protocol (SIP) for the Open Mobile Alliance (OMA) Push to talk over Cellular (PoC)}},
    pagetotal = 20,
    year =      2005,
    month =     feb,
    day =       8,
    abstract =  {This document describes a set of private Session Initiation Protocol(SIP) headers (P-headers) used by the Open Mobile Alliance (OMA),For Push to talk over Cellular (PoC) along with their applicability, which is limited to the OMA PoC application. The P-headers are used for requesting and indicating the alerting mode of the handset which is particular to the PoC application.},
}