IMS: The Importance of Testing

By Chad Hart

The IP Multimedia Subsystem (IMS) is steadily progressing from concept to reality. Despite these advances, interoperability, performance, scaling and security remain major challenges. Testing is not optional — it is absolutely crucial for success in IMS. All major equipment providers have committed to the IMS architecture and are implementing parts of it — not to mention a selection of major IT vendors and a variety of specialists. Many vendors and carriers now tout IMS as the single most significant technology change of the decade. A host of new product announcements, reports, newsletters, and articles are continually appearing. Yet it’s already clear that the conformance, interoperability, and performance challenges with IMS will be huge. How can vendors and service providers navigate these challenges as quickly and economically as possible, and realize the promise of IMS?

The Premise and Promise of IMS

IMS enables network convergence by utilizing a common IP-based core infrastructure to deliver a combination of new, content-rich multimedia services and legacy services to a variety of access networks, including both fixed and wireless. The basic idea behind IMS is to shift from “silos” to “layers” in delivering services across different access networks. There are a few premises in IMS that are now very well accepted:

• Decouple access from applications.

• Provide functions as modules.

• Use standardized interfaces, reusing as many existing standards as possible (e.g., SIP).

These may sound simple, but there are wide-ranging implications, many of which are already evident in early IMS products and trials.

Increased Complexity

While IMS ultimately aims to simplify service delivery through a common IP-based core infrastructure and application layer, migrating to this new model is an enormous undertaking. Old systems and architectures must be supported while the several dozen new IMS functions are implemented. Just keeping track of IMS is a huge headache — just the 3GPP specs for IMS require several rows of shelf space alone and there are many other standards groups involved.

Nebulous Standards

For an industry that took 12 years to standardize T1 and E1 and 15 years to standardize AIN, getting to the current IMS framework in five years is remarkable. However, many issues remain, and standards haven’t yet addressed several big areas like the definition of common security elements and security aspects such as: handing of denial of service, topology hiding, and overload protection. Legal requirements for “lawful intercept” aren’t dealt with yet, nor are the “transcoding” approaches that will be necessary when going between wireline and wireless networks. In addition to areas that are not yet addressed, there are areas that are not defined well or not addressed outside of the 3GPP including charging, OSS/BSS integration, user data management, fixed-mobile convergence, and provisions for peering.

At the end of the day, infrastructure vendors need to deliver cutting-edge products to drive sales, even when standards are not ready. As a result many vendors have differing interpretations and implementation approaches. While this is not a new problem, the new expectations for IMS have helped to accentuate these issues.
Delivering on the promise of interoperability is perhaps the foremost challenge of IMS.

Multi-Vendor Interoperability

Service providers want to mix and match network devices from multiple vendors according to their unique network needs. IMS further disaggregates network devices, creating a larger opportunity for multi-vendor deployments. In fact most end-to-end system vendors are finding they can not offer an end-to-end solution using only in-house products. This also means there is a need for multiple vendors’ equipment to interoperate in a much deeper, cleaner way than the industry has ever been accomplished in the past. Delivering on the promise of interoperability is perhaps the foremost challenge of IMS for vendors. To date, there haven’t been any “interoperability” events or conformance test suites beyond those that existed with the existing protocols IMS encompasses. However, the first real interoperability events are coming in mid 2006. Now vendors are scrambling to prepare for these tests and to avoid the negative consequences of not playing well with others.

Quality

IMS promises to accelerate convergence in many dimensions (technical, business-model, vendor and freedom-of-access) and make “anything over IP and IP over everything” a reality. However, stratification of the transport layer, control/session plane and applications create unique challenges from a service quality-assurance perspective. More network functions and interfaces means more failure points. IMS products are by definition new, which makes them particularly prone to bugs. Furthermore, while products may work in a vendor’s lab, new issues are often arise when they are attached to other vendors’ devices.

Blending fixed and mobile networks will introduce new and more complex quality challenges.

Addressing IMS Problems With Testing

The challenges of IMS can certainly be discouraging. The best way to overcome the new complexities, standards conformance, interoperability, and quality of experience issues associated with IMS is to test.

Fortunately the test market is introducing a new and improved set of test tools to help identify and resolve these issues and verify that IMS can to live up to its promise.

Start With a Test Plan

The industry is still in the early stage of development of test tools and processes that can reach across new IMS elements and converged networks. However, there are many key testing and deployment functions requirements already known for successful product development, interoperability, and deployment:

• Each component within the infrastructure must be tested for reliability, scalability, security/integrity, interoperability, and performance to ensure it meets both the vendor requirements and subsequently the service provider requirements.

• At each layer (access, control, and application) interoperability must be tested at the equipment, application, and underlying protocol level. Network equipment manufacturers will need to test their own equipment as well as other vendor equipment for interoperability and performance characteristics. Service providers will expect their vendors to provide pre-tested multi-vendor solutions as well as bring new equipment to the solution and expect their vendors to enable interoperability.

• Service providers will need to be able test across disparate internal networks as well as test across multiple external networks in order to provide the end user with a quality service and user experience. The end user will expect quality end-to-end performance regardless of device or network.

• All applications will need to be tested both separately and in conjunction with the other applications on the network to ensure compatibility, interoperability, and bandwidth availability.

• Since IMS deployments are a migration, both service providers and NEM will need to test interworking with existing network infrastructure and applications.

The variety of testing needs is broad (Figure 1). Each area includes verification under load, since scaling and performance (particularly latency) are essential aspects of testing.

Get the Right Test Tools for IMS

Proper testing tools and automation techniques can overcome this complexity and reduce development and deployment costs substantially. Looking across the many layers of IMS, is essential to successfully implement and maintain the IMS architecture. Focusing on end-to-end performance and interoperability is extremely important in order to find and resolve the issues that have the most impact on customer experience (and, hence, support cost and service revenue). Performance of IMS applications, especially latency for signaling and media, will also continue to be a focus area for quite some time. While different tools are often required for different tests, it is important for infrastructure vendors and service providers to be able to rely on as few test vendors as possible in order to quickly develop internal processes and minimize test costs. Chosen test tool vendors should be able to support the diverse IMS protocols, equipment, and applications, and offer testing tools that can perform a wide variety of testing functions. Conformance, interoperability, security, and performance remain key technical challenges for the industry.


In addition, there are a few “must have” capabilities for test automation in IMS:

• Ability to verify core elements of the IMS architecture including both positive and negative testing across signaling, media types, and applications, including vendor variants;

• Ability to verify interoperability and interworking, including legacy-to-IMS scenarios, multi-vendor situations, and effective interworking across layers;

• High-density stress and load testing capabilities, including both signaling and media;

• Diagnostics and troubleshooting insight.

Test for Success in IMS

IMS promises delivery of new applications across multiple devices, media types, and locations. Service providers of all types, as well as network equipment manufacturers, are actively progressing down the IMS path, in search of a more flexible, modular, access-independent application delivery platform. Yet conformance, interoperability, security, and performance remain key technical challenges for the industry. This is exacerbated by the sheer complexity of IMS and the fact that there are still “holes” in both standards and implementations.

Testing is always important, but it is even more crucial with IMS. Requirements for testing are shaping up to be substantially broader and deeper than the industry has seen before. Creating a test program that spans the layers, functions, applications, and lifespan of IMS deployment is challenging. But not creating a test program spells failure. Test tools and techniques for IMS are emerging, and there are significant resources — both knowledge and tools — you can bring to bear today to manage the IMS new challenges.

Chad Hart is product marketing manager at Empirix (news - alert). For more information, please visit the company online at www.empirix.com.

[Return To The Table Of Contents ]