%% You should probably cite rfc5039 instead of this I-D.
@techreport{ietf-sipping-spam-05,
    number =    {draft-ietf-sipping-spam-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-ietf-sipping-spam/05/},
    author =    {Jonathan Rosenberg and Cullen Fluffy Jennings},
    title =     {{The Session Initiation Protocol (SIP) and Spam}},
    pagetotal = 28,
    year =      2007,
    month =     jul,
    day =       9,
    abstract =  {Spam, defined as the transmission of bulk unsolicited messages, has plagued Internet email. Unfortunately, spam is not limited to email. It can affect any system that enables user-to-user communications. The Session Initiation Protocol (SIP) defines a system for user-to- user multimedia communications. Therefore, it is susceptible to spam, just as email is. In this document, we analyze the problem of spam in SIP. We first identify the ways in which the problem is the same and the ways in which it is different from email. We then examine the various possible solutions that have been discussed for email and consider their applicability to SIP. This memo provides information for the Internet community.},
}