1. http://en.wikipedia.org/wiki/IP Multimedia Subsystem 2010
2. http://www.metaswitch.com/sbc-session-border-controller/ims-architecture.aspx 2010
3. http://www.iec.org/newsletter/may07 2/analyst corner.pdf 2010
4. 3GPP TS 24.229 IP Multimedia Call Control Protocol Based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP)
5. 3GPP TS 23.228 Technical Specification Group Services and System Aspects IP Multimedia Subsystem (IMS)