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802.11n Ratification: The IT Checklist

September 9, 2009 - 0 Comments

In September the IEEE will close the final chapter on a standards ratification process that will have lasted almost exactly seven years. The IEEE will ratify the 802.11n standard for high-speed wireless, removing the final hurdle for adoption by even the most conservative of organization. Of course, many organizations have already developed quite a kinship with the standard that delivers wireless performance on par with wired networks. However, questions remain as to how to proceed now that the standard is approaching ratification. Since the introduction of the first enterprise-class Wi-Fi certified access point two years ago, Cisco has partnered with over 6,000 companies to deliver 802.11n solutions. From this experience, Cisco has developed a checklist of best practices to help companies navigate the path forward with a final, ratified 802.11n standard.

1.)           Don’t worry!  If you’ve deployed 802.11n draft 2.0 equipment today, your investment is protected.  Draft 2.0-certified equipment is fully compliant with the final 802.11n standard and will be grandfathered in to receive final standard certification for interoperability from the Wi-Fi Alliance. Client devices that are draft 2.0 certified are also fully compatible with the final standard.

2.)           Check your switching infrastructure.  Leading 802.11n access points can provide 200 Mbps of useable throughput per radio, enough to overwhelm a Fast Ethernet connection.  Access points should connect to a Gigabit Ethernet connection for the best performance. Additionally, ensure that your switches have an adequate power budget to support your access points. The good news is that leading access points can be powered by standard 802.3af Power over Ethernet.  

3.)           Phased deployments are okay.  802.11n access points can coexist with 802.11a/g access points.  If budget is a concern, look to add 802.11n access points in high-traffic areas such as conference rooms and common areas, and then add 802.11n access points to the rest of your network over time.  802.11n access points will also support legacy clients and will actually provide an enhanced, more reliable link for 802.11a/g devices.

4.)           Develop a 5-GHz strategy.  With more devices entering the network, it’s important to deploy access points for capacity. The 5-GHz spectrum is the best band to deploy in: this spectrum is less congested and offers eight times the number of channels as the 2.4-GHz band. If you haven’t site-surveyed for 5 GHz, now is the time to do so.  Use features like Cisco BandSelect to help ensure your wireless clients connect with preference to the 5-GHz frequency. What’s more, ensure your access points are Dynamic Frequency Selection (DFS)-compliant to make use of the entire 5-GHz frequency band.   

5.)           Deploy 40-MHz channels in 5 GHz.  To get the best performance, 802.11n uses double-wide, 40-MHz channels.  You’ll want to ensure that your network is configured to support 40-MHz channels in the 5-GHz spectrum. With limited frequency available in the 2.4-GHz band, you’ll want to leave these set for 20-MHz channels.

6.)           Turn on high-throughput data rates.  It may seem obvious, but troubleshooting often reveals that clients can’t connect at high-throughput data rates (those above 54 Mbps) because the access point has not been configured to advertise at those rates. Double-check these settings and turn on high-throughput data rates when you install your 802.11n infrastructure.

7.)           Select devices that support 802.11n, when possible.  Your existing installed base of 802.11a- and 802.11g-based wireless clients will continue to interoperate with your 802.11n network.  802.11n clients will achieve superior performance in the presence of 802.11a/g clients.  However, migrating to newer 802.11n-based clients will improve the overall performance of the network.  Use beam forming features like Cisco ClientLink to optimize the performance of legacy 802.11a/g wireless clients, which increases network efficiency.

8.)           Recognize that not all 802.11n adapters are the same.  There are many different types of 802.11n client adapters on the market.  While the majority is Wi-Fi-certified to the 802.11n draft 2.0 specification, many adapters use different combinations of antenna technology, which yields varying degrees of performance.  Look for 2×2 and 3×3 multiple-input multiple-output (MIMO) chipsets that will yield better performance on your network than 1×2 multiple-input single-output (MISO) or 1×1 single-input single-output (SISO) 802.11n chips. 

9.)           Improve legacy coexistence by disabling legacy data rates.  To improve capacity on your network, disable legacy data rates such as 1, 2, 5.5, 6 and 9 Mbps.  This will ensure that 802.11 protocol “overhead” takes up the least amount of time on your network.  As you increase access point density and migrate more clients to 802.11n technology, you can continue to disable legacy data rates such as 12 and 18 Mbps. Cisco recommends that wherever possible, IT should disable the use of 802.11b.

10.)         Evaluate your security posture.  802.11n requires the use of Wi-Fi Protected Access 2 (WPA2) with Advanced Encryption Standard (AES) encryption for high-throughput data rates.  Ensure that AES is turned on in your network and that your clients are set to prefer AES if an option is available. 

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