What is IP Multimedia Subsystem (IMS)

IMS or IP Multimedia Subsystem represents a 3GPP and 3GPP2 effort to define an all IP based wireless network as compared to the historically disparate voice, data, signaling, and control network elements. In plainspeak, IMS is supposed to make seamless multimedia (audio, video, live cast, etc.) experience practical to the mobile phone users.

Although there may be many potential IMS applications, key applications are:

• Video Calls
• Unified Messaging
• Push-to-Talk
• Wireless/Wireline Convergence
• Online Gaming
• Video-on-Demand
• Presence
• Consumer and Business VoIP
• IPTV
• Online Addressbook

IMS opens communication options that seamlessly combine ongoing voice sessions with multimedia elements (sharing video while talking, for example) or enrich shared applications with voice communication (for instance, talking while playing a multiplayer game). It will also be possible to change the communication mode smoothly during an ongoing session, in contrast to today’s more or less ‘fixed’ communication modes.

Jose Miguel Cansado gives a compelling use case

“Access from multiple devices and network access. Coupled with IPTV and Femto cells, as an example, you will be able to receive SMS, IM or calls on your TV screen or on your PC, even if you have been called on you cellular. With Femto cells, your presence info could be automatically updated when you reach home. Other services bundled with IPTV would include video conference from the TV, or having a voice, video or chat session open with friends on TV while watching the Super Bowl.”

IMS can provide new person-to-person multimedia communication services going beyond those available on today’s 3G networks. Because IMS is IP based, it will blend telecommunication and data services, keeping the best of both the circuit-switched and packet worlds.