1. Siddiqui, K., Kamran, M., Tajammul, S.: Comparison of H.323 and Sip for Ip Telephony Signaling. In: IEEE 4th International Multioptics Conference, Lahore, Pakistan (2001)
2. Franks, J., Northwestern, U., Hallam-Baker, P., Hostetler, J., AbiSource, I., Lawrence, S., Agranat Systems, I., Leach, P., Microsoft, C., Luotonen, A., Netscape, C.C., Stewart, L., Open Market, I.: Http Authentication: Basic and Digest Access Authentication. IETF RFC2617 (June 1999)
3. Salsano, S., Veltri, L., Papalilo, D.: Sip Security Issues: The Sip Authentication Procedure and Its Processing Load. Network 16, 38–44 (2002)
4. Andreas, S., Daniel, K.: Sip Security,Sip Group, CH-8401 (2004)
5. Geneiatakis, D., Dagiuklas, T., Kambourakis, G., Lambrinoudakis, C.: Survey of Security Vulnerabilities in Session Initial Protocol. IEEE Communications Surveys & Tutorials 8(3), 68–81 (2006)