1. Rosenberg J, Schulzrinne H, Camarillo G, Johnston A, Peterson J, Sparks R, Handley M, Schooler E: SIP: Session initiation protocol. RFC 3261. Internet Engineering Task Force 2002.
2. Rigney C, Willens S, Rubens A, Simpson W: Remote Authentication Dial In User Service (RADIUS). RFC 2865 (Draft Standard). Internet Engineering Task Force 2000.
3. Calhoun P, Loughney J, Guttman E, Zorn G, Arkko J: Diameter base protocol. RFC 3588 (Proposed Standard). Internet Engineering Task Force 2003.
4. Tsakountakis A, Kambourakis G, Gritzalis S: SIPA: generic and secure accounting for SIP. Security and Communication Networks 2011. [ http://onlinelibrary.wiley.com/doi/10.1002/sec.387/abstract ]
5. Fischl J, Tschofenig H: Making SIP make cents. Queue 2007, 5(2):42-49. 10.1145/1229899.1229911