%% You should probably cite draft-ietf-avt-rtp-gsm-hr instead of this I-D.
@techreport{westerlund-avt-rtp-gsm-hr-00,
    number =    {draft-westerlund-avt-rtp-gsm-hr-00},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-westerlund-avt-rtp-gsm-hr/00/},
    author =    {Magnus Westerlund and Karl Hellwig and Ingemar Johansson},
    title =     {{RTP Payload format for GSM-HR}},
    pagetotal = 18,
    year =      2008,
    month =     oct,
    day =       24,
    abstract =  {This document specifies the RTP payload format for packetization of the GSM Half-Rate speech codec.},
}