IMS (IP Multimedia Subsystem) is considered to be the core technology of the next generation network and an important way to address the unification of mobile and fixed networks and to introduce differentiated services such as voice, data and video.

IP = IP-based transport, IP-based session control IP-based service implementation
Multimedia = Combination of media such as voice, video, pictures, text, etc. Combination of terminals with different capabilities based on multiple accesses
Subsystem = a system that depends on existing network technologies and network equipment

The IP Multimedia Core subsystem is made up of a system of functional groups. The groups are linked by a set of standard interfaces to form an IMS management network. A functional group is not a node (i.e. a hardware entity): its implementation is open, allowing multiple functional groups to be deployed in a single node and allowing a functional group to be implemented by multiple nodes.

Network access
There are several ways for users to access IMS, most commonly using the Internet Protocol (IP), and IMS endpoints such as mobile phones, PDAs and computers can access IMS directly, terminals by simply using the IP protocol and running a Session Initiation Protocol (SIP) can have access to the IMS

IMS supports network access via

Fixed line access
e.g. digital subscriber line (DSL),Cable modem and Ethernet
Mobile access

e.g. WCDMA, CDMA2000, GSM and GPRS

Wireless access

e.g. WLAN and WiMAX

In addition telephone systems such as regular old telephone services, H.323 and non-IMS compatible VoIP systems can be accessed via New Rock MX series VoIP gateways to IMS.

IMS builds a layered, open and unified core network control architecture on top of the IP network and is an operational, manageable and billable system.