IMS — From Network Deployment to Service Delivery

By Andy Huckridge
IMS has transitioned from a concept to a “here and now” architecture. The impact IMS stands to have on revenue streams is forcing service providers and equipment manufacturers to look closely at combining existing service offerings and to pay close attention to the quality of experience (QoE) these combined services deliver. As a delivery system, IMS provides subscribers with widespread access to new and existing services independent of location or device. The architecture comprises evolving protocols and interface specifications to make possible voice, video and data services over fixed and mobile environments. IMS also offers high scalability for network expansion along with system redundancy for improved reliability.

IMS is expected to work with any wireless or fixed network that uses packet switching, including older gateway-supported telephone systems. Operators and service providers seeking to employ IMS will be able to use a variety of network architectures including their existing systems to offer services such as Voice-over-Internet Protocol (VoIP), gaming, messaging, content sharing and presence information among other applications.

One of the most important promises of IMS is the rapid introduction of new multimedia services. By separating the Application/Services Layer from the control and transport planes, new individual applications can be developed faster at lower cost. Also, service providers can use third parties for application development. Subscribers will enjoy greater service selection from just about any device. They will have broader access from workstations, cell phones, PDAs, fixed and mobile viewing devices, and the latest devices presently in development. Subscribers are expected to use many additional services, generating revenue potential for the operators and providers.

While IMS is not distinctly about developing new services, it certainly enables the introduction of new services by using InternetProtocol (IP) and the IETF-designated Session Initiation Protocol (SIP). Described in RFC 3261, SIP is an application-layer signaling protocol that starts, changes and stops sessions between participants. The 3rd Generation Partnership Project (3GPP) standardized the SIP variant used in IMS, but other protocols and functions also contribute to the viability of IMS across a variety of networks and devices.

A New Service Architecture

Properly set up, IMS core networks will interwork with 2G/2.5G and 3G cellular networks, public switched telephone networks (PSTN) and other existing VoIP networks. And while IMS network and device performance standards have not yet been fully adopted, which leaves open-ended questions as to how IMS goodness metrics will be achieved and measured. One thing is certain, however: The pressure is on to create new services despite the need to solidify standards and measurements.

Fixed and mobile convergence (FMC) paves the way for merging wireless and traditional wireline technologies. The dissimilarity of fixed networks and mobile networks is clear; they were invented and implemented at different times and for different services. Mobile networks enhance many exciting, customer appealing services while fixed services offer mainly caller ID, call back, second line and call block. Yet the two types must now come together. They need to be delivered with a single technology in such a way to provide operating benefits and costs benefits. Carriers will be able to save money by merging the cores of fixed and mobile networks, and NEMs will realize savings by offering a common architecture to service providers.

This new architecture will benefit landline providers as they stave off mobile subscriber churn. Capital expenditures will decrease significantly after some increased operating expenditures. Ultimately, a win-win situation can be expected as providers and operators offer more compelling IMS services, but the steps leading to such success will have to be assured through proper testing of equipment and systems.

Delivering IMS Based Services

Service providers and network operators are independent businesses. None is likely to use IMS and protocols in the same manner. However, all will utilize combinations of protocols depending on their family of offerings and individual strategies. To succeed, providers and operators will have to understand how and where to test their system if they want the best network performance and maximum revenue generation. The first step is getting to know how FMC relates to IMS, and the next step is to begin comprehensive testing.

Until the industry fully implements IMS networks that provide IMS services, FMC and FMC-based services must be linked to IMS. Providers and operators who do not understand this concept may lose service revenue. For the time being, IMS will carry FMC services to subscribers over FMC-capable networks that will essentially be IMS-based. IMS is expected to carry FMC-based services such as call swapping between a landline and a mobile, as well as swapping between the Radio Access Network (RAN controls transmission/reception of cellular radio signals) and the WiFi network at home. Eventually, new IMS-based services will be rolled-out on IMS-based networks. Underlying network topology, whether mobile or fixed, will be irrelevant. At that time, IMS will be in full operating mode with the transition finalized.

IMS testing over mobility and FMC should be approached by isolating packets and security gateway devices by emulating WLAN access points, millions of mobile nodes and the entire 3G mobile packet core. A test methodology is required that covers all aspects of IMS service delivery — conformance, functional and performance. As the FMC transition approaches and IMS evolves, special attention must be paid to billing systems and security threats.

IMS is a paradigm shift and has a significant impact on testing strategies. Historically, 18 months or more are required to introduce a new service. IMS can potentially reduce time to a few months, even weeks. To do so, testing strategies must be nimble which they have not been traditionally. Testers must be capable of allowing quick prototyping of new services in the lab prior to deployment. As service providers and NEMs evaluate IMS test solutions, they should consider testers that are designed to be inherently flexible to quickly craft new call flows for specific applications. These test systems should allow users to isolate individual application servers (AS) or test applications as a system, including the control plane and the AS. The IMS test systems should analyze and validate functionality, error handling, or tune an application server for performance. Furthermore, they should test most IMS applications such as Presence, Push-to-Talk, Instant Messaging, and Share List Servers.

Taking Care of Billing

The implementation of IMS is a business decision, as payment systems are an integral part of IMS architecture. Standards-based interfaces and network elements have been defined to facilitate billing. IMS changes the rules on unique/customized billing schemes to maximize average revenue per user (ARPU). These billing schemes will permit subscribers to choose from a large selection of services and products by adding or deleting offerings in real-time.

Unlike in the past when testing billing in an IMS service environment, service providers need to consider several important aspects, such as validating the billing criteria and process when adding new services, identifying and testing new billing schemes that are not limited per minute charges and ensuring that systems can handle content-sensitive billing, such as billing different type content in the same service at different rates.

Seizing Security by the Horns

Dedicated testing for threats conducted before and after deployment will keep IMS systems functioning properly, or this new technology will suffer like many unprotected enterprises. While IMS promises easy access across multiple providers, the reality of implementation still faces interoperability hurdles between legacy and next-generation networks. This implementation issue is especially true for not only security but billing accuracy as well.

Vendors and operators must carefully evaluate and verify their IMS strategies prior to full-scale deployment. IMS networks must be able to interoperate with today’s existing networks, which is why thorough network and device testing is vital every step of the way—from before deployment and throughout the deployment process.

IMS security must be managed at two separate levels — Network-to-Network Interconnection (NNI) and User-to-Network Interconnection (UNI). Service providers must ensure that when connecting to other service provider networks, traffic passes securely between the networks and that the billing information transfers in a secure manner. Currently, for service providers there are a major set of issues surrounding the users’ ability to access the network, in terms of authenticating the user and making sure they can access only the services they have been granted.

Services are the Future

IMS is a business decision that involves technology modification and creation. When a common architecture is implemented, the gate opens wide for the introduction of innovative new services to subscribers. Such new services are expected to drive the adoption of IMS and the global implementation of Next Generation Networks.

It is important to remember that the IMS architecture is for delivering services and not necessarily for advocating an inherent service. For the first time in telecom history, an architecture separates the service layer from the network’s signaling and bearer layers. IMS allows NEMs and operators to focus on a “service architecture/service delivery” approach to enhance time-to-market for new products — boosting their ability to compete in an already highly competitive marketplace.

Our new columnist, Andy Huckridge (news - alert), is Director, NGN Solutions at Spirent Communications, where he leads Spirent’s strategy for the Multimedia Application Solutions division. His responsibilities include product management, strategic business planning & market development. Andy has worked in the Silicon Valley Telecommunications industry for 12 years and has a broad background in defining and marketing products in the Semiconductor, VoIP and IMS/NGN space. He holds Bachelor’s and Master’s degrees in Telecommunication Engineering from the University of Surrey, England. Andy is active in various Forums including the Multi-Service Forum, where he is Chairperson of the Interoperability Working Group & NGN Certification Committee. Andy is a VoIP patent holder, an IETF RFC co-author and inaugural member of the “Top 100 Voices of IP Communications” list. Andy can be reached at [email protected].

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