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Optoelectronics & Communications

IMS and the next generation of mobile networks

Third-generation IP-based services' cutting-edge architecture promises multimedia convergence for mobile network technology.
19 April 2006, SPIE Newsroom. DOI: 10.1117/2.1200603.0133

Most cellular networks are based on 2G (second generation) or 2.5G technology. However, carriers around the world are upgrading to third generation wideband code-division multiple access (WCDMA) and universal mobile telecommunications system (UMTS) to support multimedia services such as music and video downloads. To this end they are keeping close watch on a new addition to 3G technology: the IP multimedia subsystem (IMS).

IMS uses an architecture that is based solely on IP (internet protocol), and expands from the core of the network (the infrastructure) to its edge (connected devices like cellular phones). In the context of cellular networks, IMS brings real-time and pre-processed multimedia services to a mobile environment. Examples of supported multimedia services include voice-over IP (VoIP), video conferencing, video sharing, and push-to-talk (PoC).

In brief, IMS means convergence between mobile, fixed, and broadband services. As an open architecture, it facilitates the art of creative communication via new services, some of which are still being developed and so are unknown. At the very least, it will replace the so-called ‘intelligent’ networks of classical telephony with truly intelligent networks that can fully support a future that includes internet-based communications.

For product developers and manufacturers, this represents a huge opportunity. Respected market researchers estimate that the required core infrastructure for IMS will cost several billion dollars per year. Currently the technology is in the trial stage: major mobile and classical circuit switch operators are investigating the prospects of migration to packet-based networks. For many, IMS presents the path to fixed mobile convergence. There is no doubt that, as this migration proceeds, we will witness the rise and fall of new types of service providers and virtual operators.

IMS uses a SIP (session initiation protocol) signaling-based architecture that addresses the needs of mobile operators for session management, security, mobility, quality of service (QoS) and charges for usage. In addition, SIP allows applications for mobile communications to be combined with Internet services in a modular and extensible way. Specified by the Third Generation Partnership Project, IMS supports multiple access cellular technologies, including the global system for mobile communications (GSM) and general packet radio service (GPRS) technologies, WCDMA, wireline broadband, wireless local-area network, and so forth. In the long run, IMS will facilitate migration to a pure IP architecture that will include the radio access network. Ultimately, therefore, IMS will mean seamless multimedia applications across different types of networks, whether wireless or wired.

The technology will be implemented with three-layered architecture as indicated in Figure 1. The application-service layer contains applications and content servers that provide the logic and value-added services for end users. It includes standard service enablers such as presence information, telephony services, and group management, using SIP application servers.

Figure 1. The IMS architechture has three layers, as shown.

The session control layer contains servers for managing calls or sessions over the network. The SIP server that implements the call session control function provides registration of endpoints, information on roaming, and routing of SIP signaling messages to appropriate application servers. Other functions include provisioning, charging, and operation and management. Interfacing with other non SIP-based networks is handled by media gateways.

Finally, the transport and endpoint layer includes the peer devices that initiate and terminate SIP signaling, as well as the backbone and access routers that carry bearer services such as voice and video telephony. This connectivity later also provides the media gateways to convert classical voice services into VoIP.

At SKY Mobile Media, our Technology and System Engineering Group is designing and extending our SKY-MAP Platform to support IMS clients. Work is already under way with SIP-based PoC, and VoIP is next. SKY's Engineering Group in Bangalore is implementing IMS from block diagrams into C++ code.

Our initial implementation of PoC is designed to conform with Open Mobile Alliance (OMA) 1.0; conformance was tested at the OMA Test Fest in Seoul, South Korea. We also envisage support of presence and group information features. Our clients include the main building blocks: SIP, SDP (Session Description Protocol), SIMPLE (Session Initiation Protocol for Instant Messaging and Presence Leveraging Extensions), XCAP (XML Configuration Access Protocol), and specific applications such as VoIP and video conferencing.

Naser Partovi and Amnon Ptashek
SKY Mobile Media
San Diego, CA
Naser Partovi is President and CEO of SKY, which provides a stands-based, open, portable, multimedia platform for handsets and converged multimedia devices. Prior to joining the company, Mr. Partovi worked at Nortel and was Managing Director of Enterprise Partners, the largest venture capital organization in Southern California.
Amnon Ptashek, CTO of SKY Mobile Media, is responsible for leading the system architecture team, defining the technology roadmap, establishing corporate IP, and identifying and managing technology partners.