(IP Multimedia Subsystem)
IMS is a general-purpose, open industry standard for voice and multimedia communications over packet-based IP networks. It is a core network technology, that can serve as a low-level foundation for technologies like Voice over IP (VoIP), Push-To-Talk (PTT), Push-To-View, Video Calling, and Video Sharing. IMS is based primarily on SIP (session initiation protocol).
For users, IMS-based services enable person-to-person and person-to-content
communications in a variety of modes – including voice, text, pictures and
video, or any combination of these – in a highly personalized and controlled
IMS is a back-end, foundational technology that enables other services, not something a user would interact with directly.
For carriers, benefits of IMS include increased flexibility for carriers to offer new 3G services, and lower costs.
The idea behind IMS is to eventually move all voice and multimedia communication (mobile and fixed) to flexible, packet-based technologies derived from Internet protocols. It is intended to eventually replace all circuit-based technologies currently used in mobile networks, although it can easily be phased in, in a piecemeal fashion, integrating with circuit-based technologies and existing billing systems, etc.