IMS is the target of massive investment by network operators and looks set to become the de-facto standard for the delivery of next generation mobile services.

Value-added services have always been a feature of mobile networks. 2G GSM networks introduced SMS messaging and also allowed the user limited access to the Internet via WAP data calls. GPRS brought more advances, however it is only with the introduction of 3G that mobile networks have the opportunity to deliver bandwidth-hungry, internet-style applications and services.

IMS provides a framework that not only allows network operators to offer IP-based services, but also allows them to charge by content rather than byte count. This can be achieved because all user requests for IMS IP services are routed through the IMS core (as SIP messages) as opposed to going straight out onto the Internet. In addition, the application servers that provide these services are part of the IMS network and can provide charging information. IMS also offers tangible benefits for the user. As any user of free Internet VoIP can tell you, the quality of a VoIP call cannot be guaranteed and can be inferior to a conventional phone call, suffering from both delay and sound quality issues. To address these types of problems, the IMS architecture has a Quality of Service (QoS) mechanism built-in. IMS also allows new services to be added more quickly and allows applications to be combined together, leading to a richer user experience.

Architecture

The IMS architecture is best described in three elements: the access networks, the IMS Core, and the Application Servers.

A major benefit of the IMS architecture is its emphasis on access independence. As well as connections from 2.5G and 3G mobile networks, IMS also allows PCs to connect via the Internet (DSL / Broadband). Access for 2G mobile phones and landline phones (via PSTN) is achieved through the use of gateways.

In any mobile network, the user has to be able to roam. A consequence of IMS's access independence is that a user can roam, not just physically, but also between different connection methods. For example, if a user has a Wi-Fi enabled handset, they can dynamically switch between using Wi-Fi and GPRS as they go in and out of Wi-Fi hotspots, and continue to access the same services.

The IMS Core is responsible for authenticating users and setting up IMS sessions using the Session Initiation Protocol (SIP). A powerful aspect of SIP networks is that a user is globally addressable via their SIP URI (e.g. SIP:matt@sip.emccsoft.com). Once a session has been set-up, SIP hands over control, and the actual data transfer is handled via the appropriate media server. One of the most important functions of IMS is to ensure the Quality of Service of the connection through the media server.

Any number of Application Servers can be connected to the IMS Core to provide both telephony and non-telephony services. A number of generic services are available across all applications, such as presence and group management.

Applications

The main applications and services which are likely to play an important part in the uptake of IMS are:

Voice over IP (VoIP)
Standard voice call services delivered using IP rather than circuit switching.

Push To Talk over Cellular (PoC)
Walkie-talkie style voice communication.

Presence
Centralised service providing a user's presence status (busy / offline / do not disturb, etc).

Messaging (e.g. IM)
It is likely that many types of messaging services (SMS, e-mail, IM, voicemail) will merge.

Video Sharing and Conferencing
Traditional videoconferencing facilities, plus the ability to share a video stream during a voice call.

Multiparty Gaming
Presence information will allow gamers to see which other users are online and ready to play.

Combined or Blended Services
Applications will be designed to use multiple IMS services in one session, for example to allow gamers to see a video of their online opponent.

One of the key features of IMS is the ease of setting up and trialing new services, so the list of potential applications will grow as network operators search for the next "killer app".

Conclusion

IMS appeals to all the players in the mobile industry: Network operators can increase revenue by charging for new services, which are cheaper for them to deploy using standard IT equipment and open standards; Equipment vendors, handset manufacturers and third party application developers all get the chance to develop and sell the new services and infrastructure required.

The key question is whether end users will want to pay network operators for IMS services. However, the type of rich, blended services that can be provided, along with guaranteed Quality of Service, and almost universal adoption, will ensure that IMS has a significant impact on both the mobile and fixed communication industries.

About EMCC

EMCC Software is a leading provider of mobile solutions and development services. With comprehensive experience in open mobile OS development and enterprise solutions, EMCC Software has been working within the Symbian, Linux, Java and Windows Mobile communities since 1998. Our wide-ranging expertise includes platform development, communications, messaging and UI creation. Our clients include mobile industry leaders. EMCC Software specialises in consulting, development and training services and has developed a portfolio of leading-edge smartphone software solutions.

Further information about EMCC Software Ltd can be found at www.emccsoft.com. Provide feedback on this article by e-mailing article@emccsoft.com