• 12/11/2008
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802.11n: Wireless Rookies Need Not Apply

New standard is complex, and even with careful planning, it may not pan out for everyone.
Before 11n networks can be installed (or current 11a/g networks can be upgraded to 11n), organizations will need to survey the spaces to be covered or resurvey areas where current WLANs live. This is because 802.11n works in the same frequency slices (2.4 and 5 GHz) as 802.11a/g networks.

For most of us, the site survey has become an exercise in merging the virtual with the physical, using a modeling tool like AirMagnet Surveyor or Ekahau Site Survey to virtually plan WLANs, followed by feet-on-the-ground verification.

Post-installation support means monitoring the airspace to find competing or offending signals and packet analysis with commercial or open source tools to reveal connectivity or application issues.

These basic premises don't change with 802.11n, but the underlying mechanics can take on a whole new feel, depending on which of the many options and operational modes are invoked.

802.11a/g spectrum analyzer tools from AirMagnet, Cisco, Fluke Networks, MetaGeek, and others will still find noise and interference. It's logical to expect that analyzers will eventually detect 802.11n devices along with everything they can classify today.

For survey products, 802.11n really raises the bar. Cells tend to have increased data rates at farther distances, so you'll need to relearn the fundamentals of survey procedures. The new standard can use multiple channel bonding that doubles spectrum width to achieve higher data rates, so survey tool providers need to accommodate the new options in their various allowed combinations for 11n cells. MIMO antennas in various configurations can drastically alter a given cell shape and size. Again, survey and modeling tools must address all 802.11n variables to be as effective as possible.

In addition, because one goal of the survey process is to predict and ensure (as much as possible) minimum data rates, 11n-oriented survey products must deliver graphical "what-if" reporting abilities that reflect hundreds of potential scenarios for each access point that's being considered.

Wireless packet analysis is already complex in 11a/g networks, and it gets even more so with 11n. Because of MIMO, the location of the client becomes critical in attempting to get an accurate read on the traffic. Ideally, the capture happens at one or both endpoints. Although the wireless payload will remain the same in 11a/g and 802.11n networks, traffic headers and how traffic is fragmented may differ, which may be a concern to those who like to go deep on packet analysis.

802.11n's channel bonding, different "guard intervals" that manipulate interframe spacing, frame aggregation options, and the number of antennas, will redefine what wireless traffic looks like. Analysis tools must support the full suite of options in the draft standard in order to be effective when the final version is approved.

For WLAN administrators who've been in the game for a while, 802.11n brings a whole new bag of intricacies to be reconciled, both before and after installation. Some existing tools--mainly spectrum analyzers--are still relevant in their current incarnations. But for packet analysis and survey work, make sure your tools are tuned to 802.11n, or you'll be missing a lot.

Evolution Of 802.11n
2004 2007 2008 2009/2010
Work begins on 802.11n standard Draft 2 of 802.11n completed; Wi-Fi Alliance starts interoperability testing Finalization of Draft 7 of 802.11n base standard and some features Additional options for 802.11n to be finalized next year; ratification expected in early 2010

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