The IP multimedia subsystem (IMS) as specified by the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), has been adopted, and will be adapted as required, to support session-based services, and other services based on session initiation protocol (SIP). This Recommendation describes how the IMS can be used in the NGN context following the fundamental principles described in [ITU-T Y.2001] and [ITU-T Y.2011]. This Recommendation identifies the IMS for use in NGN and describes the use of the IMS in providing the IP multimedia service component of the NGN functional architecture and describes its relationships to other service components. It further identifies those IMS architecture documents that are relevant in the context of NGN. For more detail refer to [ITU-T Y.2012].