IMS, IP Multimedia Subsystem tutorial

- a summary or tutorial of IMS, IP Multimedia Subsystem, providing the highlights of its operation and structure.

IMS, or IP Multimedia Subsystem is having a major impact on the telecommunications industry, both wired and wire-less.

Although IMS was originally created for mobile applications by 3GPP and 3GPP2, its use is more widespread as fixed line providers are also being forced to find ways of integrating mobile or mobile associated technologies into their portfolios.

As a result the use of IMS, IP multimedia subsystem is crossing the frontiers of mobile, wire-less and fixed line technologies. Indeed there is very little within IMS that is wireless or mobile specific, and as a result there are no barriers to its use in any telecommunications environment.


IMS basics

IMS, IP multimedia subsystem, itself is not a technology, but rather it is an architecture. It is based on Internet standards which are currently the major way to deliver services on new networks. However one of the key enablers for the architecture is the Session Initiation Protocol (SIP), a protocol that has been devised for establishing, managing and terminating sessions on IP networks. The overall IMS architecture uses a number of components to enable multimedia based sessions between two or more end devices.

One of the elements is a presence server that handles the user status, and this is a key element for applications such as Push to talk over Cellular (PoC) where the presence, or user status is key to enabling one user to be able to talk to another.

With users now needing to activate many sessions using different applications and often concurrently, IMS provides a common IP interface so that signalling, traffic, and application development are greatly simplified. In addition to this an IMS architecture means that subscribers can connect to a network using multiple mobile and fixed devices and technologies. With a variety of new applications from Push to talk over Cellular (PoC), gaming, video and more becoming available, it will be necessary to be able to integrate them seamlessly for users to be able to gain the most from these new applications.

It also has advantages for operators as well. Apart from enabling them to maximise their revenues, functions including billing, and "access approval" can be unified across the applications on the network, thereby considerably simplifying this area.


IMS development & history

IMS was developed by the cellular industry but to meet the growing needs across the mobile, fixed and IT / computing networks.

It was developed out of a need for the telecommunication industry, and in particular the cellular telecommunications industry to be able to allow for ubiquitous access to multimedia services from any terminal.

IMS grew out of the political landscape of the day. This shaped many elements of its design and architecture, and as a result, it needs to viewed with this in mind.

The IMS standards were developed by a group called 3G.IP which was formed in 1999. This group was soon taken under 3GPP where its work could be better harmonised with the work of the cellular industry who it appeared would be the main users.

Accordingly IMS is defined within the 3GPP standards and its development can be tracked within the different releases.


3GPP Release Approx Year Details
Rel-5 2001 First introduction of IMS
Rel-6 2003 IMS emergency services
Combinational services
Voice call continuity
Rel-7 2005 Single radio voice call continuity (SR-VCC)
Multimedia telephony
Rel-8 2007 IMS centralised services
IMS continuity services
Multimedia interworking between IMS and CS networks
IMS multimedia Telephony and supplementary services
Rel-9 2009 IMS emergency calls over GPRS and enhanced packet system, EPS
Enhancements of IMS customised alerting tone service
IMS restoration services
Rel-10 2010 IMS services continuity - inter-device transfer enhancements

One major push for its use came at Mobiel World Congress 2010, where GSMA announced they were supporting what was then termed the "One World" initiative for carrying Voice over LTE, VoLTE. As the system was based around the use of IMS, many operators then decided it was necessary to incorporate IMS capabilities within their networks.


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