@techreport{ietf-sipping-call-flows-01,
    number =    {draft-ietf-sipping-call-flows-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-ietf-sipping-call-flows/01/},
    author =    {Chris Cunningham and Jonathan Rosenberg and Steve Donovan and Alan Johnston and Henning Schulzrinne and Robert Sparks and Kevin Summers and Dean Willis},
    title =     {{Session Initiation Protocol Call Flow Examples}},
    pagetotal = 218,
    year =      2002,
    month =     aug,
    day =       1,
    abstract =  {This informational document gives examples of Session Initiation Protocol (SIP) call flows. Elements in these call flows include SIP User Agents and Clients, SIP Proxy and Redirect Servers, and Gateways to the PSTN (Public Switch Telephone Network). Scenarios include SIP Registration, SIP to SIP calling, SIP to Gateway, Gateway to SIP, and Gateway to Gateway via SIP. Call flow diagrams and message details are shown. PSTN telephony protocols are illustrated using ISDN (Integrated Services Digital Network), ANSI ISUP (ISDN User Part), and FGB (Feature Group B) circuit associated signaling. PSTN calls are illustrated using global telephone numbers from the PSTN and private extensions served on by a PBX (Private Branch Exchange). Example SIP messages used for testing during SIP interoperability test events include SIP 'torture test' messages, and messages with invalid parameters, methods, and tags.},
}