September 15, 2009

How Reliable Is Your Wireless Local Area Network?

Recently, I was trying to purchase a few books from Amazon.com, however, the site was inaccessible. *Gasp* I actually went to Barnes & Noble Online to make my purchase, even though I strongly prefer Amazon. The whole experience made me think about the importance of system reliability.

Because Wi-Fi is both a job and a hobby, my thoughts quickly turned to wireless networking. Which prompts me to ask, "Is your Wireless Local Area Network (WLAN) reliable?"

What resiliency options are available on enterprise class wireless gear? I suggest looking for the following features:

* Access Point (AP) Power: APs should be able to be powered via a standard AC power outlet or through Power over Ethernet (POE). Ideally, these would be on two different circuits.
* WLAN Controller Power: If you have WLAN controllers in your IDF/MDF, they should have two power supplies that are dual homed to two different power sources. Power supplies should be "server grade" with a mean time between failures (MTBF) of at least 100,000 hours. The power feed should be conditioned. WLAN controllers should also be connected to a battery back-up.
* Multiple Uplink Ports: Each AP should have multiple uplink ports. This allows the AP to be connected to different switches, which gives the WLAN not only port level resiliency, but switch level resiliency. The uplink ports should be capable of many different modes, including failover, link aggregation, and port mirroring. The WLAN controllers should also have multiple uplinks into the core of your network.
* Multiple Radios: At a bare minimum, each Access Point should have two separate radios. Beyond redundancy, multiple radios in a single platform allow for a dedicated wireless threat sensor providing intrusion detection & prevention functions. This form of threat management can maximize the uptime of your WLAN.
* Automated Channel Selection: Enterprise class access points should have the ability to scan the wireless environment and automatically select channels that are not in use in a given area. This minimizes the chance of what's called "co-channel interference", which could severely degrade the performance (and therefore the usability) of your WLAN.
* Automated Cell Sizing: Similarly, enterprise APs should have the ability to automatically adjust their power level so that neighboring adjacent access points have just enough overlap for seamless roaming. Too much overlap can also cause co-channel interference and wreck havoc on the overall stability of the WLAN.
* Meshing Capability: Some vendors call these Wireless Distribution System (WDS) links, or wireless bridges. While not absolutely critical in today's WLANs, a meshing capability allows the system additional flexibility if one portion of the WLAN is cut off from the rest of the network. In those scenarios, mesh links may be able to provide an alternative backhaul link or some self-healing capability.

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