Rapid Application Development with DIAMETER in IMS

By Arun Handa

The IP Multimedia Subsystem (IMS) defines a major milestone in the 3G wireless network evolution, paving the way to an all-IP network. IMS is not just a technology, but also a reference architecture that embodies the best-of-breed infrastructure from the IP world and principles from the traditional telecom domain. The
IMS concept leverages heavily on a SIP-based architecture that has been proven in VoIP networks. It also utilizes and extends the Authorization, Authentication, and Accounting (AAA) paradigm deployed in mobile-IP networks, including QoS capabilities, with DIAMETER.
Evolving from the RADIUS protocol, DIAMETER provides an extensible framework not just at the message and command-level, but also at the application-level that extends its utility from Mobile-IP, EAP, and NAS applications to the 3GPP framework. In this article, we examine the driving factors behind a need for rapid application development for DIAMETER applications that deliver these important functions. To put things in perspective, we need to understand the role of these applications and where IMS is headed.

The conversation about IMS is agog with buzz, with debating camps of supporters and disbelievers. With the return of industry momentum after the telecom downturn and excitement generated from new multimedia and Internet technologies, several top-tier operators are planning rollouts within the next 12–18 months.

However, the sluggish pace of 3G deployments coupled with overcapacity and underutilization in existing network infrastructure has created skepticism among the wireless community for further evolution. At the same time disruptive technologies ranging from 802.11x and IP phone service from Skype, Vonage, and cable companies continue to chip away at overall market share.

The most significant argument in favor of the converged multimedia services is the harmony through standards. The 3GPP in the wireless domain and TISPAN in the wireline domain have worked diligently towards the standardization of an end-to-end IP network embodied in the IMS reference design. Both groups concur that SIP and the underlying protocols from the IP community are to power IMS services. Furthermore, the 3GPP definition of IMS has also attracted interest from WiMAX and cable broadband equipment providers, promising to play a pivotal role in moving towards even broader convergence while increasing average-revenue-per-user through new multimedia offerings for all network operators. While convergence looks certain in the foreseeable future, the means to that end are still speculative.

IMS Solution Providers and Operators

IMS could very well be the final frontier for the telecom operators battling the freedom and speed of adoption of the Internet. There is urgency to either provide differentiated services or to be relegated to a bit-pipe provider. Telecom operators, are well known for their cautious approach to any new technology rollout. Given the high capital investment and customer expectations of high-quality service, operators generally plan new technology rollouts in four distinct phases:

• Definition — Is it technologically and economically viable (ROI)?

• Decision — Should we allocate resources and what are the risks?

• Deployment — How to plan a full service rollout?

• Commercial Realization — Launch and go to market.

From an operator’s view, today IMS is in the Decision phase. Operators are now looking to IMS solution providers to demonstrate the operational viability of IMS that goes beyond the proof-of-concept trials of push-to-talk over cellular and video sharing.

Telecom solution providers, for both infrastructure and services, are anxious for new sources of revenue and are trying to carefully time the market entry of their offerings and to position themselves solidly in this emerging market. The pressure is building up on IMS solution providers to rapidly build applications and services around the following:

• Carrier-grade reliability and security that have not been stringent in IP communications.

• New innovative services that will hopefully prove to be the next killer app.

• Interoperability with an ecosystem of solution providers in both the circuit switched and IP network domain.

• Interworking with and support of legacy services.

Solution providers coming from diverse network backgrounds face a dilemma in providing solutions in the IMS architecture. Can existing infrastructure provide a foundation to accelerate the deployment of new applications or does everything get built ground-up?

IMS was designed with best-practices of telecom networks, which includes both VoIP and Cellular networks. The product elements in the control and media plane, from the contemporary VoIP networks, can be leveraged to a fair extent. However, it must be kept in mind that IMS goes beyond the wireline-VoIP evolution. The innovative fixed mobile convergence (FMC) solutions are trying to provide an interim option.

VoIP evolved slowly. Early offerings were interesting, but quality of service was poor. VoIP ultimately became successful as the result of a combination of innovation and de-facto standards allowing low-cost service approaching the quality of circuit switched networks. The success of VoIP has impacted fixed line access to such an extent that “triple play” multimedia services and now “quad-play” with the addition of the wireless element, seems to be a competing point for wireline operators. After quad-play, only one piece of the puzzle remains — mobility.

To a large extent that is what IMS addresses — a juxtaposition of all these five elements, but achieved through a more harmonized industry standard. More important is the fact that each aspect gets broader treatment — take access for example. It is an access independent network. Like all previous network and service build-outs, it is crucial that offerings adhere to the standards. In the case of IMS, a divergence from standards exposes vulnerability to the operators in the form of service reliability and possible security breaches.

Rapid Application Development

IMS allows the delivery of a multimedia user-experience, and its architecture can be viewed in four distinct planes. The Control Plane provides the necessary signaling and coordination of events to establish, maintain and teardown multimedia sessions. The Media Plane provides for the processing and trans-coding of audio and video streams. The Service Plane provides the logic to enable multimedia applications. While these three planes have been a part of most communication networks, the new Policy Plane provides the ability to guarantee the required quality of service.

The media plane can be implemented with a rich set of mature products available from the VoIP industry today. This includes media gateways, controllers, and servers. The bigger challenge lies in implementing the remaining planes, although SIP building blocks can be used. Typically there are two approaches – ‘IMS-ification’ of existing infrastructure or deciding to build from scratch. Either approach calls for a rapid development framework to allow lower development costs, a driver for IMS.

Most top-tier equipment vendors have tried to leverage existing infrastructure in the traditional circuit-switched or VoIP networks by enabling these elements with IMS specific protocols and support. A well-designed HLR (Home Location Register) can be extended to an HSS (Home Subscriber Server) for multimedia profiles and enabled with DIAMETER to exchange this information with other IMS elements. Session Border Control providers are looking to move into evolving into the P-CSCF function. Application Providers in the charging, content, convergence, messaging, and location space, to name a few are looking to enter the IMS ecosystem rapidly as well.

Core network signaling has been transformed from SS7-based protocols to SIP, DIAMETER, MGCP, RTP, and COPS. While SIP drives the control-plane all the way from the user terminal to the IMS core network bringing in rich media services and presence, it is DIAMETER that truly enables some of the critical functions in the IMS core network.

DIAMETER provides the support for the essential functions of Subscription, Charging, and Policy in the network. Subscriber-related data that defines all the service-related parameters resides in the HSS. Access to this data from session controllers and application servers is made possible by the DIAMETER protocol. Mechanisms for both online and offline charging for multimedia services is enabled by the DIAMETER Ro/Rf interfaces. The function of obtaining resource reservation, QoS support at the edge of the network is provided by the Policy in the Gq interface. Evolving from the more ubiquitous RADIUS protocol providing the AAA support, DIAMETER has provided the 3GPP-IMS network with a more versatile and extensible mechanism to support these interfaces.

In summary, with the telecom operators affirming their commitment and urgency to IMS, the telecom solution providers must continue to position themselves with differentiated offerings rapidly. Enabling existing service infrastructure with DIAMETER application support for instance, using a rapid application development paradigm can bring products to market quickly that fit in the IMS architecture and meet the carrier-grade demands of the operators.

Arun Handa is chief technology officer at IntelliNet Technologies (news - alert), a provider of application development solutions for the converged network.

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