Although the advanced carrier service IP Multimedia Subsystem (News - Alert), or IMS, has been a buzzword within the industry for some time now, there are many compelling reasons for carriers to move to this architecture. Some of these include: a single common platform for delivering voice and multimedia services to both fixed and mobile endpoints, lower network operational costs through managing just a single infrastructure, and a platform capable of rapid innovative service deployment.

For a better understanding of this architecture and its benefits to carriers, MetaSwitch’s white paper, titled “An Introduction to IMS: The Technology and The Motivation,” gives a good introduction to IMS and explores some common reasons for adopting IMS as an advanced carrier service.

According to the MetaSwitch (News - Alert) white paper, one of the most compelling reasons to deploy IMS is that it can provide a common platform for delivering voice and multimedia services to a mix of fixed and mobile endpoints. Service providers who today offer both mobile and fixed line services may use a common shared transport infrastructure, but are typically not able to achieve convergence at the services layer. Class 5 switches deliver services to fixed lines, while Mobile Switching Centers deliver services to mobile phones, and these are completely separate network elements.

Enhanced services may be provided by Intelligent Network (IN) techniques, but fixed and mobile networks use different and incompatible IN protocols (AIN, WIN and CAMEL), thus they cannot share the same enhanced services platform either. It is possible to develop advanced carrier services that bridge both worlds, but such solutions are expensive to develop since they need to talk to two sets of protocols.

IMS addresses this problem by providing unification of fixed and mobile voice and multimedia services, according to the white paper. Unlike physical access network technologies that are used by fixed and mobile endpoints, IMS is essentially independent of the type of network access used. Because IMS is 100 percent IP, with all signaling based on SIP, a common set of infrastructure components including HSS and Application Servers can serve any mix of fixed and mobile endpoints.

With IMS, it is possible to deploy rich, high-value advanced carrier services such as hosted business voice to both fixed endpoints and mobile endpoints without having to make any service-related distinction between them, the white paper states.

Furthermore, the paper highlights the special capabilities of SIP, such as forking, which allows a user to have a fixed phone and mobile phone with the same phone number without having to do anything special to support this in the network. Also, SIP signaling in the IMS network could provide a means to converge SMS and Instant Messaging services with the integration of presence information across any mix of fixed and mobile phones.

Another motivation for IMS is that it can provide a unifying architecture that supports all of the different strands of VoIP based network modernization with a single, consistent approach. The HSS provides a single repository of data about all subscribers, so there is only one place in the network to go to add new subscribers and to define what services a subscriber gets.

Finally, IMS provides a comprehensive blueprint for voice and multimedia telephony in 4G mobile networks, addressing all of the key issues such as roaming and the management of Quality of Service (QoS) and bandwidth allocation in the access network, concludes the MetaSwitch paper.