Wireless Infrastructure Support
WLAN networks use a shared, license-free, Radio Frequency (RF) medium for communications. The operational challenges of running a wireless network are unique and different from wired networks. Some common issues often affecting WLAN performance are:
Coverage and Capacity
WLANs typically consist of Access Points (APs) distributed across the enterprise. RF signal strength wanes as the distance from the transmitting source increases. Indoor RF propagation is strongly affected by scattering and multipath in the environment, which in turn depends on the obstacles and building characteristics. Careful site survey and planning is needed to optimize the placement of APs to assure robust coverage where needed.
Despite best efforts, most enterprise deployments still suffer from coverage holes. Apart from zones where consistent signal fading occurs, there may still be areas where the practical wireless throughput is lower than expected. Being unable to connect to the wireless network or having a poor connection can be frustrating and result in reduced productivity.
Sometimes, despite good signal strength, users experience reduced throughput from the WLAN. This often happens when other users are consuming excessive shared bandwidth or when the AP is overloaded. One slow connection can bring down the whole network. This often happens when a user on the periphery of an AP’s coverage (operating at lower data rates) is utilizing the network excessively. Since WLANs use a fair channel sharing algorithm, the slow user gets to access the channel as frequently as the fast user. The situation is similar to a fast car being stuck behind a slow truck on a single lane highway. Another common performance bottleneck is excessive clients connected to a single AP.
Noise and Interference
The RF medium used by WLANs has ambient thermal noise as well as interference introduced by other devices radiating energy in the same frequencies used by the WLAN. WLANs operate in the Industrial, Medical and Scientific (ISM) license free band (2.4 GHz and 5 GHz), shared by other wireless protocols and devices such as Bluetooth, cordless phones, microwave ovens, wireless cameras, etc. Excessive noise and interference will increase the packet error rate in the WLAN leading to reduced wireless throughput and potential loss of connectivity.
Since RF interference is hard to “see” and quantify without sophisticated spectrum analyzers and other costly RF equipment, IT is often left guessing at what the potential source of wireless performance degradation might be. Many interference sources are transient and only detected intermittently, exacerbating the complexity of wireless troubleshooting. For example, a microwave oven in the office might be on during lunch break, seriously degrading the WLAN in its vicinity during mid-day.
Co-channel interference is another common problem for WLANs. Since APs often limit coverage to provide wireless access over a large area, a frequency reuse pattern can be used to allow two adjacent APs to operate without collisions. The number of non-overlapping channels in the 2.4 GHz band is limited to three. This forces enterprises to re-use the same frequencies across the deployment. This creates co-channel interference where two APs and their associated devices are operating on one channel causing increased collisions resulting in higher packet error rates.
Even with proper coverage and reduced interference levels, enterprise IT often receives support calls associated with wireless connectivity issues. For example, the WLAN could be healthy but a user may have a wrong security key, a bad wireless driver, wireless supplicant issues or other tools preventing wireless connections. Alternatively, the user’s client might be fine, but the AP could be misconfigured, an antenna might have fallen off or the AP may have a hardware problem. Sometimes a wireless connectivity problem may not even be a wireless access issue – the problem may be on the wired side of the network (a bad gateway for example). Having to rule out coverage, capacity, noise and interference problems is daunting enough, not to mention user error, device/software misconfigurations and wired network issues.
Another common problem affecting mobile wireless clients is roaming. This particularly impacts Voice over WLAN (VoWLAN) clients with stringent jitter and latency requirements. When a mobile client roams, it may have to switch its AP connection. Roaming between APs efficiently and securely is a challenging requirement. Troubleshooting roaming problems is even more challenging. A static connection between a client and a fixed AP can be analyzed with a laptop analyzer. However, a mobile client associating with several APs makes laptop based analysis cumbersome. A distributed monitoring system can automatically lock onto a mobile client and provide a centralized, consolidated view of its behavior as the client roams, significantly simplifying troubleshooting.