Feature The Network Computing Masterclass Series From Network Computing Magazine Vol 17 No 2 - March/April 2008 … going beyond technology and product.
The Wireless Networking Masterclass series - in association with Extricom. Enterprise Wi-Fi; avoiding the pain Wireless LAN (WLAN) has progressed from the humble, standalone, 802.11 wireless access point (AP) - a technology created for individual users - to ubiquity in the enterprise; APs are as common to the boardroom as the home. However, enterprise Wi-Fi quality has not kept pace. Prevailing vendor architectures comprise an element manager (controller) and multiple, individually configured APs. These systems essentially operate like a constellation of hot-spots, meaning that in the enterprise environment, Wi-Fi performance may be worse than a simple SOHO implementation, with users competing for AP access. "So What?" Wi-Fi
IT managers might be inclined to say, "So what?" For some, WLAN represents a cheap extension of the wired network, offering convenient, ad-hoc connectivity, rather than for business-critical applications. But anything more than consumer-class Wi-Fi, is overkill.
This minimalist approach is increasingly outmoded, as organisations look to leverage the full capabilities of wireless, data, voice, video, and RFID. WLAN must raise its game to match these increased expectations. Unfortunately, cell-planned networks, the most common Wi-Fi architecture, may be unable to deliver. Inconvenient Truths
When considering your WLAN options, you must bear in mind that the 802.11 wireless specification was originated for consumers. That is, it defines the interaction between a single AP and a small number of users. So when large numbers of users access multiple APs for bandwidth intensive applications, they run into the limitations of 802.11, including:
Channels are scarce - WLANs operate in a limited set of channels in two frequency bands. The 2.4 GHz band (the popular choice) has just three non-overlapping channels, requiring careful balancing to avoid co-channel, inter-AP interference. Without efficient use of the available channels, available WLAN capacity and bandwidth is unlikely to meet user needs.
Mileage will vary - The farther you are from an AP, the slower the communication rate of your wireless client. Such users consume more network bandwidth for each communication, while experiencing a reduced grade of service. The challenge, then, is to achieve an AP layout that provides a steady and consistent connection rate to all users across the entire service area. Easier said than done, since traditional cell-planned architectures are either designed for coverage (the signal is widely available) or for capacity (maximum number of connected users) but not both. Optimising WLAN performance in such systems can be a difficult trade-off.
Wireless, but not Mobile - The great irony. 802.11 is designed for portability (static users), not for mobility (users on the move). In a Wi-Fi network, the client device is normally expected to make the decision to "roam". Poor handoff decisions cause real-time applications (e.g. voice, VPN security sessions) to suffer degraded operation. To avoid disappointment, be certain to understand what "seamless" mobility delivers. Building an enterprise grade WLAN
It's clear that new approaches are required so that corporate WLANs can meet the demands of the entire enterprise. Any architecture has to be flexible enough to deal with environmental and application challenges, maximising coverage, capacity and mobility, without compromise; it must deliver guaranteed service throughout the deployment area.
The wireless industry has fielded a number of technological innovations to achieve these goals. One such is the Channel Blanket, in which all APs transmit and receive on the same channels, and the wireless signal of multiple APs is aggregated into blankets of coverage. Wireless clients associate directly to the switch rather than an individual AP, ensuring a uniform grade of service, robust connectivity through AP path diversity, and maximum performance across key areas, including coverage, capacity, mobility, security, and quality of service. APs can be placed in any density to achieve a targeted throughput, without the channelisation constraints of cell-based solutions.
Whichever architecture you choose, the goal is clear. Benefit from the consumer grade price points of Wi-Fi clients, but achieve business class WLAN infrastructure. NC In the next issue of Network Computing, this Master Class series will discuss the truths and myths of 802.11n. Network Computing and Extricom (www.extricom.com/wirelessfundamentals) invite reader comments and questions, relating to items discussed in this series. email: Ray.Smyth@BTC.co.uk
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