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Wireless-N Road Map

Here are six tips for getting started with 802.11n.

All IT managers want the performance improvements of up to 600 megabits-per-second throughput and the increased coverage that the new 802.11n wireless standard promises. But with the IEEE standard still not fully resolved and pre-standard products on the market, it’s important to do your homework and consult with your network manufacturer before moving forward. Here are six points to consider when you plan that upgrade to 802.11n:

1. Look for modular access points: While all indications are that any final changes to the draft 2.0 standard will be upgradeable with software, there’s no guarantee that this will be the case for every change. This means you may need to replace your access points (APs) when the 802.11n standard is finally issued in early 2010.

Before buying, ask the manufacturer what kind of replacement policy they have and how easy or hard it is to swap out the gear. You may want to look for modular products that let you more easily swap out the networking cards. On the other hand, note that the current generation of 802.11n products don’t yet support the full theoretical potential of 600Mbps speeds. You may find yourself upgrading hardware in a few years anyway if the higher speeds are important to your organization.

2. Find site survey tools that can handle 802.11n: The 802.11n standard offers much greater coverage than the existing 802.11g and 802.11a standards. Because it achieves this through new technologies such as multiple input/multiple output (MIMO) and channel bonding, it’s important that your site survey tool understand 802.11n to get an accurate survey. Active survey products such as AirMagnet have been updated to communicate with 802.11n networks.

Many wireless manufacturers are in the process of upgrading their predictive survey tools to understand 802.11n, but you need to be sure — so ask. One workaround if you are using an older survey tool is to do a site survey for 802.11a, which will give you the access point density you need for 802.11n. This makes good sense, especially if you want to support legacy protocols. However, if you’re doing a greenfield installation and plan on supporting only 802.11n, you’ll be best served by a newer site survey tool.

3. Check to see if your wireless access points require more than 15.4 watts: Most Power over Ethernet (PoE) switches support the 802.3af standard and can supply a theoretical maximum of 15.4 watts of power to PoE-capable devices. After loss from cabling and power supplies, however, the real power output may be closer to 12 to 13 watts. A new standard, 802.3at, promises to supply up to 24 watts, but it’s not ready yet.

Power requirements of 802.11n access points are all over the map — some manufacturers require more than 15.4 watts, others claim to work within the current standard. For those that claim to work with standard 802.3af power, be sure you understand exactly how much power the access point requires and how it behaves if it doesn’t get that much. For example, some 802.11n APs start scaling back functionality if they don’t receive enough power. If your manufacturer’s access points require more power than 802.3af can deliver, your options include pre-standard 802.3at switches from manufacturers such as Cisco Systems, or midspan PoE injectors from companies such as PowerDsine. Whichever you choose, your best bet is to test the switches and APs in a real-world environment before you go live.

4. Consider how aesthetic concerns may affect performance: Wireless gear used to be fairly simple, with a single antenna, two at most. Today, some of the new products are downright cumbersome, with as many as six antennas. You may also have to hide APs in a drop ceiling, which could become an issue if it interferes with the wireless signal, putting a damper on performance. In some cases, you may need to plan to roll out a few extra APs to provide solid coverage and keep your users happy.

5. Understand potential network design issues: There has been a debate for the past few years on whether an 802.11x wireless network should be based on standalone “thick” APs or “thin” APs powered by a central controller. The earliest wireless networks were primarily thick, meaning that most of the intelligence resided in each access point. As wireless networks expanded, the industry moved toward a thin AP model; the access points were essentially dumb radios, and all the intelligence resided in centralized controllers.

There’s now some concern that with the increased throughput of 802.11n, the centralized controllers (and the uplinks to them) won’t be able to handle all the traffic. Whether or not this is an issue at your company will depend on your deployment size, the location of your controllers and the usage patterns on your network. While there’s no right or wrong answer, it’s an issue you should understand and monitor as you roll out 802.11n.

6. Focus on spectrum and channel planning: The growing consensus is that the 5 gigahertz spectrum is best for enterprise wireless because it is a much cleaner space than 2.4GHz. 802.11n complicates the issue by allowing you to run in either the 2.4GHz or 5GHz space. You’ll need to decide which frequencies to use, and whether you want to support the legacy 802.11a/b/g protocols.

Many of the 802.11n APs on the market feature dual radios, a good choice at least for the next couple of years because many of the notebooks you’ll support will work only with those legacy standards. If you haven’t deployed 802.11a widely, consider using one radio to run 802.11n in 5GHz and the other to run 802.11b/g in 2.4GHz. You could also add 802.11n to the mix in 2.4GHz, but keep in mind that it limits your ability to enable channel bonding, a performance-enhancing feature in 802.11n that lets you “bond” two 20 megahertz channels into one 40MHz channel. Because 2.4GHz allows for only three nonoverlapping channels, you’ll be able to run only one 40MHz bonded channel, which would severely limit your deployment options.

Dan McCarriar is director of network and production services at Carnegie Mellon University in Pittsburgh.

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May 21 2009 Spice IT

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