Wireless-local-area-network (WLAN) technology first became prevalent in the small-office/home-office (SOHO) market. In that forgiving environment, convenience often outweighs performance concerns. But as 802.11 technology extends to the enterprise, wireless-system designers and developers must face the enterprise market's performance-based realities. Enterprise WLAN networks are evolving to support business-critical data and voice applications, large numbers of network users, and diverse network elements. All of these elements have historically been part of the wired-Ethernet LAN. Because network managers and end users have long been accustomed to the high performance of the Ethernet, they increasingly expect uncompromised service quality and data throughput.

Despite the fast adoption rate of WLAN technology, comprehensive test metrics and methodologies for benchmarking wireless equipment are only now beginning to emerge. The traditional testing methods that were developed for Ethernet-based hardware and networks aren't applicable. They can't handle the increased complexity and differences in WLAN devices and end-user requirements.

Currently, there are no generally accepted test methods or metrics for evaluating the performance of wireless networks. This issue has led wireless-network designers and vendors to rely primarily on custom-built testing solutions. Such solutions attempt to mimic the conditions of a wireless network.

However, recent developments in WLAN testing promise to hasten the acceptance of 802.11 technology in the enterprise. In a series of three articles, we will delve into metrics and measurement techniques that have been specifically developed and defined for wireless networks. We'll also present a practical example of an enterprise application—voice over WLAN—and the metrics related to it. This first article reviews the end-user and network requirements that are unique to wireless networks. It also examines common types of WLAN tests while describing traditional WLAN-testing solutions.

Ethernet-device performance is essentially a measure of the packet-forwarding rate. In a wireless network, however, the performance measurement has to take into account several other factors. These factors include automatic data-rate adaptation, roaming, security, and quality of service (QoS). Most of the differences between wired and wireless protocols spring from the innate mobility of wireless users and the associated physical-layer dynamics.

Unlike wired LANs, which have a stable physical layer, wireless networks rely on an inherently erratic physical layer: air. Air is subject to random interference from the radio frequency (RF) that's emitted by 2.4-GHz phones, microwave ovens, radar, adjacent channels, and objects in motion. In addition, protocols that deal with mobility and open-air transmission simply don't exist in the wired world.

Compared to wired networks, WLANs are subject to a completely different set of end-user and network needs. What conditions define a real-world wireless environment in an enterprise? Network managers must guarantee network stability and performance for the end users' business-critical, bandwidth-intensive applications. Those applications require:

• Mobility and roaming: The mobility of the WLAN end user has a major impact on WLAN networks and the complexity of the 802.11 protocols. Mobility can result in throughput loss and service disruptions. For example, the position of a client device with respect to an access point (AP) is critical for maintaining throughput. As users move between access points (roam), they create random demand and location spikes. The roaming process is complicated. It requires the completion of multiple steps while the end user is in motion. At the same time, the network connection must be kept transparently available to the user.
• Scalability: Unpredictable user and traffic loads are the result of users joining and leaving the network randomly. For example, wireless airport networks carry unpredictable traffic loads. Three hours before flight departure, an AP in an airport waiting area might have one user. Three hours later, 1 to 200 users might all be trying to use the same AP.

In addition to the end-user characteristics, certain network aspects become increasingly important to measure in the wireless paradigm:

• Interoperability: Large enterprise networks often consist of thousands of access points and tens of thousands of clients. The diversity and widespread nature of wireless technology requires multiple vendors to work in a single network. Single users must work in multiple public and private networks. The need to test interoperability is therefore critical to ensuring the successful deployment of Wi-Fi equipment.
• Performance: Mission-critical applications must deliver reliable performance and QoS. Although 802.11 technology is progressing in terms of capacity, it still relies on a shared medium to provide connectivity. Wireless solutions must perform well. They also must implement and deliver sound QoS features, which support applications that require guaranteed service levels.
• * Security: Security requirements are more stringent for WLANs than for their wired counterparts. After all, wireless networks are susceptible to intruders, who can easily tap into the network with an antenna. If they're improperly implemented, 802.11i encryption and authentication protocols can be a significant drain on the performance of wireless networks. A client that has been authenticated in one place in the network must maintain authentication while roaming. The authentication process is lengthy and can disrupt a session if it isn't conducted properly. As a result, the security process can affect network performance, roaming times, and association times. Testing must characterize the effectiveness and efficiency of security implementations.

A variety of tests must be performed to make sure that wireless equipment meets the complicated requirements of wireless networks and end users. The complexity of the 802.11 protocol requires testing to verify network and device functionality, capacity, interoperability, and conformance prior to deployment. As vendors strive to deliver WLAN products that meet the diverse needs of both users and wireless networks, they usually perform the following test categories:

• Certification testing ensures that wireless equipment meets industry- or government-established minimum requirements like interoperability, safety, and emissions. In 802.11, this testing is driven by the Wi-Fi Alliance (WFA). The WFA is a vendor-based industry forum that is focused on testing and certifying product interoperability for the good of the consumers. The WFA has defined industry-accepted interoperability test suites. It also has contracted labs to perform certification worldwide. Once certified, a product is allowed to bear the Wi-Fi label.
• Performance testing ensures that the product meets expected network results. Performance characteristics are universal. But the mobility, roaming, and scalability factors are unique to the wireless world. Performance testing must measure the range of the wireless device and its throughput capability. In addition, it must account for unique wireless phenomena like the number and mobility of users, security schemes, and QoS. Devices must perform appropriately under fault conditions, such as a sudden surge in throughput or other unexpected event.
• Co-existence testing verifies that the product is versatile and robust in diverse environments. Performance is tested in the presence of interference to prove that a system can intelligently avoid interfering with other wireless systems. Examples of such other systems include analog wireless phones and wireless technologies like Bluetooth, Ultra Wideband (UWB), WiMAX, and ZigBee.
• Conformance testing validates that the product completely adheres to the specifications of the 802.11 standard. Complete conformance testing and protocol analysis is needed to verify that a device is compliant with the IEEE 802.11 specification. This development-level test is usually performed using sophisticated and expensive signal-generation and analysis tools.