%% You should probably cite rfc4964 instead of this I-D.
@techreport{allen-sipping-poc-p-answer-state-header-05,
    number =    {draft-allen-sipping-poc-p-answer-state-header-05},
    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-answer-state-header/05/},
    author =    {Jan Holm and Andrew Allen and Thomas Hallin},
    title =     {{The P-Answer-State Header Extension to the Session Initiation Protocol for the Open Mobile Alliance Push to Talk over Cellular}},
    pagetotal = 32,
    year =      2007,
    month =     mar,
    day =       5,
    abstract =  {This document describes a private Session Initiation Protocol (SIP) header (P-header) used by the Open Mobile Alliance (OMA) for Push to talk over Cellular (PoC) along with its applicability, which is limited to the OMA PoC application. The P-Answer-State header is used for indicating the answering mode of the handset, which is particular to the PoC application. This memo provides information for the Internet community.},
}