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The Power of 802.11N

One can barely open a trade rag these days without reading about the arrival of the next generation of wireless standards -- 802.11n. It’s always exciting when new technology hits the market, especially when that new technology truly lives up to the hype. Of course, as with anything new there’s always a bit of misinformation that exists before folks have made it through the learning curve. As I follow the comments of various industry pundits, I’m starting to see a reoccuring theme -- misinformation on how to power 802.11n access points.Power over Ethernet (PoE) has helped many an IT shop save money and improve application availability. Its value extends beyond wireless to include other peripherals, including IP Phones. But arguably, PoE’s true calling is in obviating the need for AC power in the ceiling and by default, simplifying and reducing the cost of wireless deployments. However, with the emergence of 802.11n, a new power paradigm is emerging. Here are the facts:The 802.3af standard provides up to 12.95 watts at the remote end of the Ethernet cable to power a variety of devices.To perform at full capacity, dual radio 802.11n access points require greater than 12.95 watts. Thus, our conclusion:Currently, 802.3af is not adequate to fully power dual radio 802.11n access points. That is, without some trade offs.Despite these facts, a number of industry players are claiming to power their dual radio 802.11n access points with standard 802.3af power. While at face value the statement is true, the devil is in the details. The truth is simple. Powering dual radio 802.11n access points with standard 802.3af power will result in a reduction in performance. Here are some different ways in which performance will be impacted:1. Up to 60% reduction in coverage area (requiring additional access points to cover the same facility)2. Reduction in throughput (disable transmitters, reduce CPU clock rate, etc.)3. A loss of services (e.g. security)4. Limiting to a single radioWhat does this mean for the business deploying 802.11n? To realize the full value of their investment, the business must invest in power options that deliver full power to the access point. Options that promise support for standard 802.3af PoE for dual radio 802.11n access points don’t come without significant performance implications. IT must assess whether investment in these suboptimal solutions is worth it. Cisco offers four alternatives that each deliver complete power:1. Enhanced Power over Ethernet - Cisco has innovated beyond the 802.3af standard to deliver up to 20 watts of power from a single Ethernet port across select members of the Catalyst switch family. This option offers the greatest performance with the lowest operational impact.2. Power Injector - The Aironet 1250 Series supports power injectors that can deliver adequate power to support full operation.3. Local AC Power - Access points within proximity of a power outlet can deliver full performance with AC power.4. Standard 802.3af -- The Aironet 1250 Series can fully power a single 802.11n radio with standard 802.3af power. This is ideal for businesses that chose to only deploy on a single frequency (2.4GHz or 5GHz).Other options such as the nascent 802.3at PoE standard will emerge over the next several quarters.The next several months promise to be exciting as businesses start to experience the true power of 802.11n. The inadequate power alternatives offered by other providers will leave IT questioning the true performance of 802.11n. Only by treating next generation wireless as an integrated wired and wireless decision can businesses truly unleash the power of business mobility.

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1 Comments.


  1. Can the power injector work on 110 v and /or 220 V? This is an important consideration for the design and deployment… propoer provisioning of power source.

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