Since their commercial debut in 1999, wireless LANs based on the IEEE 802.11 or Wi-Fi standards have become a mainstay in enterprise networking. As the business has grown, both the applications and the technology have developed in ways that were not foreseen. Where they originally supported convenient e-mail and Web access in meeting rooms and other public areas, WLANs are increasingly being called upon to support real-time voice, video and high-bandwidth data applications with vastly different capacity, performance and security requirements.
On the technology front, WLANs have developed from simple configurations using stand-alone access points (APs) to sophisticated solutions based on a central controller that supports a network of specially designed APs providing RF management, integrated diagnostics, and rapid handoffs for mobile users. One of the most important developments impacting the entire space is the high capacity 802.11n radio link. Where the earlier WLAN radio technologies supported data rates up to 54 Mbps, 802.11n theoretically could top out at 600mbps or up to 300mbps from current 802.11n APs.
While greater capacity is good news for users, it also puts greater strain on the infrastructure. That 802.11n-enabled network must be capable of supporting the full range of applications, including large file transfers, voice and video for teleconferencing and medical consultation applications. A higher capacity wireless network will attract more users. However, if the infrastructure components are not scaled to support that additional traffic, the users will not reap the full benefit.
WLAN Architectures: Centralized or Distributed
The earliest wireless LANs were built using stand-alone APs, which differed little from the models that were used for home networks. However, enterprise wireless LANs might require hundreds of APs, each of which would provide coverage in a different part of the facility in a configuration similar to a cellular telephone network.
The limitations of stand-alone APs became painfully obvious as users spent weeks positioning the APs, selecting the channels to be used in each area and tuning the transmit power to ensure adequate coverage. That process had to be repeated on a smaller scale each time a new AP was added to the network. The solution to this problem came with the introduction of centrally-controlled WLAN switching systems where the controller selects the channels, adjusts the power and adjusts the settings to provide good coverage and to compensate for changing radio conditions.
