What is the IP Multimedia Subsystem?

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  • Written By: Kurt Inman
  • Edited By: Lauren Fritsky
  • Last Modified Date: 09 November 2019
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The IP Multimedia Subsystem, also known by the acronym IMS, is an architecture for multimedia delivery. Originally designed for mobile phones, it can enable multimedia sessions between fixed or wireless telecommunication devices. It also utilizes the Internet Protocol (IP) infrastructure to transport multimedia data to and from connected devices. IMS can be used by service providers to enable video teleconferencing, messaging and web browsing for all of their subscribers. It can also be used to provide multi-user gaming, Voice over IP (VoIP) and streaming video.

In 1999, a telecommunications industry group named 3G.IP created the first IP Multimedia Subsystem specification. It was later adopted by the Third Generation (3G) Partnership Project as part of their 3G wireless phone standard. Its goal was the delivery of Internet services through General Packet Radio Service (GPRS) technology. Several features were added to IMS and published in 3G Partnership Project (3GPP) releases throughout the 2000s. These included service centralization, connection to fixed broadband devices and non-GPRS network support.

A rich communication suite is provided by the IP Multimedia Subsystem for both service providers and end users. It offers a common and reusable platform for efficient development with open standards. It can also maintain network bandwidth to provide high-quality service. Providers can utilize IMS to deliver and charge for distributed interactive applications and real-time services. At the same time, users may benefit from seamless text, voice and video regardless of their location or the device being used.


The complex multimedia enabled by IMS can require several sessions of multiple applications to be active at once. The IP Multimedia Subsystem manages these with the Session Initiation Protocol (SIP) and other Internet protocols. Controlling connections, sessions and services with common Internet protocols simplifies signaling and software development. It also increases compatibility and cooperation since all providers utilize a proven standard communications backbone.

To facilitate the smooth interaction of many types of applications and devices, the IP Multimedia Subsystem is divided into three layers. The transport layer handles all communication with devices such as computers, 3G phones and Personal Digital Assistants (PDAs). It also interfaces with SIP mobile phones and legacy wire-line phones, composing packets from analog and digital data as needed. Session initiation and signaling are also performed by this layer.

The control layer of the IP Multimedia Subsystem manages packet movement between the transport layer and the application layer. It also manages calls, service charges and all user profiles. The presence server, critical for push-to-talk and other services, is also found in the control layer. The application layer isolates application servers from user devices and network control issues. Many servers are supported in this layer, allowing IMS to handle several types of applications and users simultaneously.


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