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Scalable load testing targets multi-service RF network gear

Posted: 01 Mar 2005 ?? ?Print Version ?Bookmark and Share

Keywords:tektronix? tool? design lab? 3g? 3g radio?

In the mushrooming world of 3G (third generation) mobile RF connectivity, simulating the real-world environment can be tough during deployment of today's multi-service audio/video/Internet products. The goal, of course, is to ensure QoS (quality of service).

Whether you're a wireless device maker, or a network operator, it's imperative that you verify the performance of your products and components before they're released, or placed on your network. But, making valid checks of a network that might be called upon to handle video, audio and Internet access can be a formidable task.

When I discussed this situation with Tektronix product marketing director for monitoring and protocol test Othar Kyas, he confirmed there's been a "glaring need" for tools that can easily simulate real world traffic conditions in design labs, manufacturing plants, and within operations facilities. "About 70 percent of emerging 3G radio access network problems are related to radio interface issues," says Kyas.

Volume, protocols and distribution
Tektronix's new LTS21, priced between about $300,000 and $1.5 million, shapes us as a configurable load test system. Addressing the needs defined above, it's capable of actually emulating a wireless traffic environment.

In use it can help you verify mobile network elements and component performanceunder realistic conditions. To do that, it generates and analyzes both control-plane (where call set-up procedures are handled) and user-plane traffic (even moving users), simulating busy networks with variable traffic volumes, protocol types and distributions.

Using the LTS21, you can establish load test conditions, and hopefully shorten your product's development cycle.

Look Ma, no code
With traffic modeling tools and a pre-defined library of test scenarios, you can create real world wireless conditionswithout any manual code writing.

Even complex test set-ups can be streamlined, using the LTS21's call generation model and intelligent drag-and-drop interface. It makes use of automated objects instead of manual scripting. Once set up, the LTS21 can make wireless load measurements such as capacity, and perform performance and stability tests.

Capacity tests enable you to verify the maximum number of subscribers, sessions, or adjacent network elements that your wireless system's RNC (radio network controller) can support. Capacity testing can also help determine the effect of various configurations on memory usage per subscriber or session.

Similarly, performance tests let you verify the maximum processing rates at which an RNC can handle external requests. Performance tests can also gauge system capacity by sending external requests above supported rates. Finally, stability tests validate RNC stability and robustness over time, under various load and stress conditions.

Call and session management, handovers, integrity protection, ciphering and compression are all supported by the LTS21. It also automatically simulates distinct protocol layers, easing standards compliance testing.

A distributed system
As a distributed system, the LTS21 runs on a central Linux-based server, with Windows-based clients. It also uses rack-mounted so-called probes. The system's probe plug-ins are CompactPCI-based, letting you easily plug in new test modules as needed.

You can also add chasses to an LTS21 system. There are a dozen cPCI slots per chassis. Thanks to these modularity hooks, an LTS21 is quite scalable, and can support in excess of 20 concurrent users, each user defining and programming test cases, configuring them, and executing them.

From days to hours

As Tek's press release notes, the LTS21 uses a graphical human interface. The GUI's intelligent objects can be combined into user-defined traffic profiles. Kyas says that that approach lets program generation be cut from days to hourseven in the hands of semi-skilled operators. "It can dramatically shorten the time to first test," he says. "No tedious and error prone command line interface is used."

Kyas says that the LTS21's automatic protocol emulation also lowers risk, as there are fewer errors, and you can conduct more tests, too. No test design personnel are required. Network elements can be stressed, and that can reduce the impact of unexpected errors, too, especially during acceptance test phases of a product's development. "In a network," says Kyas, "you can stress it to the point that it will break or be impaired."

That kind of capability is just what's needed, regardless of whether you're a communications equipment manufacturer or a network operator. In fact, as a piece of equipment goes from field trials and installation and commissioning, there are acceptance tests that network operators usually make. Manufacturers must prove to operators that the proposed equipment works!

The LTS21 bridges that gap. Once the equipment is on the network, the network operator can then use the LTS21 during network maintenance and optimization phases, as well as for QoS management and resource provisioning.

Along with its LTS21, the company is also rolling out a network and service analyzer. For operators, it targets so-called UTRAN (Universal Mobile Telecommunications System Terrestrial Radio Access Networks). The new NSA (Network and Service Analyzer) is a 3G software application for the company's existing K15 monitoring platform.

The portable K15 protocol test platform can troubleshoot live and trial 3G, 2.5G and 2G mobile networks. It uses the cPCI architecture to host several boards to connect to multiple interfaces, including E1, T1, J1, STM-1 (optical) and 10/100-Mbit/s Fast Ethernet.

For its part, Tek's new NSA for UTRAN is based on automated analysis algorithms. These let operators identify service problems and map them to root causes. Tek contends the system will reduce test time, letting you focus on problems rather than data acquisition.

The system minimizes manual effort, too, yet maximizes the information available to you when monitoring UTRAN interfaces. To do that the NSA for UTRAN provides automated instrument configuration for Iub, Iur, Iu-CS, and Iu-PS interfaces. This automation reduces the time required to obtain and analyze data.

Network topology discovery
The new application also provides automated network topology discovery. This enables effective troubleshooting of live 3G networks. KPIs (key performance indicators) also give you the ability to relate breakdowns per service (i.e. voice, video, or packet), per network element (cell, NodeB, RNC, SGSN, MSC), per call and per subscriber (IMSI, MSISDN) to communication protocol events in the network infrastructure.

This built-in intelligence lets you navigate through data results, narrowing the scope of a problem to isolate its root cause. According to Kyas, without these applications, it would take technicians hours to identify the proper network parameters (such as VPI, VCI, CID) for configuration before starting to perform troubleshooting.

Cell overlapping matrix
Also, because UMTS cell coverage areas overlap one another, network operators face challenges to prepare reliable cell planning to guarantee high QoS. When a UMTS handset reaches the boundary of the coverage area of a cell, you have to guarantee that interference coming from adjacent cells won't interfere with RF link quality.

If interference is too strong, service deteriorates, reliable handover operations to adjacent cells can be impeded, and user connections can be terminated. "Enabling reliable handovers, and managing the levels of interference between cells requires careful balancing," says Kyas.

Displaying interference
Using NSA for UTRAN, Kyas says operators will be able to display interference levels between any two cells. Using the product's Cell Overlapping Matrix application, network operators will be able to actually see the influence of adjacent cells on the cell under analysis.

The Cell Overlapping Matrix will therefore reduce time for network reconfiguration tasks, such as populating the RNC cell neighboring list, or creating a cell scrambling code plan.

You get multi-user support, too. The NSA for UTRAN lets you cut costs by sharing the use of one protocol analyzer in a server environment. Additionally, the user interfaces are automated, reducing the time your technicians might spend configuring the system and collecting data.

What's more, the approach enables senior technicians to focus on critical tasks, increasing productivity of test teams.

Okay, what will such a system cost? Tek says the NSA for UTRAN package is priced from about $30,000 to $100,000, depending on the number of lines you wish to monitor. A K15 host typically goes for about $70,000 to $100,000.

- Alex Mendelsohn

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