The wireless enterprise environment operates under very different conditions than wired networks. As a result, this environment requires a fresh outlook on testing. For wireless LANs (WLANs) to succeed in the enterprise, developers must rely on system-level test solutions. Such solutions must produce repeatable outcomes, scale beyond a single device to a network, and provide systems designers with an automated solution that will decrease the cost per test.

As discussed last month in the first of this series on 802.11 testing, traditional WLAN-system testing methods are inherently at odds. Examples of such testing methods include isolated screen rooms for controlling RF interference and large open spaces for testing mobility. The fact that these methods are at odds makes it difficult to test real-world conditions, such as mobility and roaming while controlling random RF emissions. In addition, such homegrown solutions are hindered by high costs and logistical issues.

Aside from having homegrown solutions at their disposal, wireless systems designers have had a variety of off-the-shelf test equipment. This equipment focuses on point-to-point tests at the physical layer, such as spectrum analyzers, signal generators, and multipath simulators. Such equipment can't efficiently test wireless networks as systems, however. An effective system-level test solution must scale beyond single devices (clients and access points) to the network itself. It must provide the ability to test the WLAN as a system. In other words, it has to precisely analyze Layer 2 performance and the interdependence of Layer 1 and Layer 2 under various mobility and load conditions.

Thankfully, there's good news for wireless systems designers. A new generation of wireless testing solutions has emerged in response to the limitations of homegrown and point-to-point testing solutions. These solutions provide the repeatable outcomes, system scalability, and test automation that will enable the enterprise adoption of WLAN technology.

Emerging wireless test solutions control RF by individually isolating the RF devices in the test. To achieve this isolation, they use a cabled RF medium and vary the RF signal strength using attenuators. This approach provides a completely controllable test bed. It also produces a more regulated test because of the following:

• Cabling the RF increases RF accuracy.
• Enhanced isolation techniques provide interference immunity.
• RF attenuation emulates RF mobility.

The result is a test solution that produces repeatable test outcomes.

Using cable-based solutions that provide a controlled-RF environment, wireless systems designers can test real-world conditions in a controlled setting. They can then scale tests beyond single devices to entire networks. Test outcomes are repeatable and more accurate. In addition, this type of solution can be digitally controlled. A programmable software engine can thus provide automation, which enhances scalability and lowers the cost per test.

The benefits of this approach are:

Repeatability: Consistent, repeatable outcomes and measurements are nearly impossible in open-air environments. The problem is that RF interference will vary in each iteration of multiple tests and in different locations. But a cabled, controlled-RF testing environment provides the same test setting every time. It offers the highest level of repeatability and efficiency, while still allowing the simulation of real-world conditions like mobility and roaming. In addition, test setup is easier because the complexity of controlling RF interference is removed. Organizations can save money, as the time spent retesting due to inconsistent results is minimized.

Testing can be further enhanced if the system uses device isolation instead of room isolation. The isolation of individual components allows testers to control inter-device interference and create controlled channel interference in the same test setup.

Scalability: If the controlled RF environment is properly architected, system designers can scale WLAN testing from a single device to the entire network (FIG. 1). Users can configure an entire WLAN network and provide system-level testing of actual access points (APs), clients, and other wireless devices. Networks can be tested under a variety of traffic and client load conditions. Problems can then be found in the laboratory instead of at a customer site.

Client and traffic load emulation enable the development of test setups that re-create a busy network environment for the devices under test. Each emulated client can be individually addressed on Layer 2 (MAC) and Layer 3 (IP). The simultaneous active clients that provide standard Wi-Fi functionality, such as security and quality of service (QoS), should each have the ability to send and receive wireless traffic. They will then provide an extremely flexible and diverse configuration.

Because the testing is conducted in the lab, test setups needn't be complicated and expensive. The ability to control RF in the lab increases testing efficiency. It allows system designers to easily design and conduct system-level stress-test scenarios for mobility, roaming, and other conditions. Previously, testing for such conditions could only be conducted in large open areas.

Automation: Another advantage of newer test platforms is their programmable test tools. These tools provide users with an automated method of configuration and traffic monitoring. To analyze the effect of mobility on both device and network performance, for example, users can automatically configure any network device and dynamically position any network node. Combined with the ability to control RF interference, the programmable software engine allows users to analyze real-world scenarios (i.e., hidden stations, overlapping basic service sets (BSSs), roaming, and rate adaptation) while simultaneously varying settings like security, QoS, and client load.

Automation saves money and time by standardizing tools, processes, and training across organizations, geographic boundaries, and the industry. Many test platforms in today's market are standardizing on Tool Control Language (TCL)—a simple-to-use and very flexible scripting language. In addition, an automated test method supports the simple, effective setup and reuse of test configurations, allowing for repeatable test execution over time. This repeatability greatly reduces the time spent on quality assurance and benchmark test processes. As a result, the programmable platforms that provide automated testing dramatically reduce time to market and the cost of test.

In the life cycle of a wireless product, vendors must continuously test and re-test the product. Each time the hardware or software is changed to add functionality, fix an anomaly, or support a new standard, the vendor must re-test to ensure that no adverse effects were caused by the change. Functional and regression testing are only the start of the testing cycle. Interoperability testing, certification testing, conformance testing, and—most importantly—performance testing are of great significance to the success of a product that's being deployed in live networks. In addition, vendors may want to conduct more in-depth tests, such as testing coexistence with other wireless technologies.

Thorough testing of a wireless device can be long and complex. But a controlled and managed test environment, such as the one described in this article, allows accuracy and automation. It also increases the efficiency of bringing products and product versions to market.

Functional testing: This type of testing qualifies standard and vendor-specific product features and functions. Some functional tests are simply a validation of the correct device behavior, such as the configuration and operation of features. Others—like security—have significant interoperability relevance. Features that have major performance implications also are important. An example is a roaming algorithm. Often, functional testing is tedious and labor intensive. Configuration automation and test-procedure automation save considerable time, as this test is repeated for every version of a product.

Interoperability testing: Such testing ensures that diverse pieces of equipment operate together. Interoperability is a major requirement for networks in the enterprise, public hot spots, and the home. Initially, interoperability testing validates compatibility with a vendor's own equipment. Next, compatibility with other vendors' equipment is tested. Most vendors rely on Wi-Fi Alliance Interoperability Certification to ensure inter-vendor compatibility.

Certification testing: In addition to standard safety and emissions certification, reputable wireless-LAN equipment is expected to pass the Wi-Fi Alliance certification tests. Wi-Fi certification allows vendors to use the alliance's coveted logo on the product. It also provides a capabilities certificate that attests to the different band, security, and QoS tests that the product has passed.