IMS: IP MULTIMEDIA SUBSYSTEM
Internet Protocol (IP) Multimedia Subsystem (IMS)1,2 was defined in 1999 by 3GPP (3rd Generation Partnership Project). e first IMS specifications from 3GPP appeared in Release 5 (evolution from 2G to 3G), when SIP-based multimedia was added. Several releases have been edited by 3GPP, such as Release 6 in September 2005, Release 7 in late 2006, and Releases 8, 9, and 10. ese releases provide the following features:
• Release 5: Session registration, initiation, modification, teardown and deregistration; SIP compression between UE (User Equipment) and IMS network; Data transfer between user information storage (i.e., HSS (Home Subscription Server)) and call session control function (CSCF) entities; Data transfer between user information storage (i.e., HSS); and Application Servers (AS), etc.