Deciding What’s Important When Upgrading to 802.11n
The 802.11n specification has been ratified since 2009, but many of its capabilities remain an enigma, especially for those who don’t have the time or inclination for a semester-long course in RF. And let’s face it, that shouldn’t be required when deploying 802.11 equipment. So, let’s alleviate the mysteries, simplify the technologies, and determine what’s important when upgrading to 802.11n.
Greenfield Deployment or Mixed Upgrade?
First and foremost, you must consider your environment when contemplating a move or an upgrade to 11n. There are two overall environments to consider. The first is Greenfield, or an environment where there is currently no 802.11 wireless deployed. Here you are starting from scratch with your wireless deployment. This gives you more room to leverage the new capabilities of 11n without interfering with current equipment.
If you already have a wireless LAN in place utilizing 802.11a/b/g technology, you are working in a mixed environment, and need to carefully consider the impact that new equipment will have on existing equipment. And keep in mind that RF knows no boundaries, so evaluating how close you are to neighbors who may have a wireless LAN is part of the equation. Mixed environments introduce some additional variables, so what you deploy and upgrade will differ slightly from a Greenfield deployment.
However, if you’re deploying in a Greenfield environment, it’s safe to assume everyone is getting new gear, so go for the 3-stream. And don’t worry about the occasional visitor or remote employee who visits with a 2-stream device. The technology is backward compatible, so these users will still be able to connect to your network, albeit at the lower data rate.
One of the most obtrusive upgrades of 11n is channel bonding, the ability to combine existing channels in either the 2.4 or 5GHz band to double the RF bandwidth available to send signals (from 20 to 40MHz), thereby doubling the data rate for wireless users. Though obtrusive, this is an attractive option since it’s been available in most 11n equipment shipped since the draft 11n standard was in place, and all that’s required is a simple configuration change to enable the feature. The downside of channel bonding is that is reduces the number of available channels for legacy 802.11a/b/g equipment, so carefully consider its use in mixed environments. And again, you must keep your neighbors in mind. For example, if the company next door specifically tuned their closest AP to you to channel 11 because you had adjacent APs on channels 1 and 6, and you then decide to use channel bonding with channel 6 and a higher channel, you will most certainly create interference for your neighbor on channel 11, creating at least some degradation for their wireless users. To mitigate these effects, in anything but an absolutely clear Greenfield environment, we recommend that you use channel bonding in the 5GHz band only, where the channel spacing is greater than in the 2.4GHz band and the interference effects of channel bonding are therefore less severe.
Aggregation (AMPDU/AMSDU) and Short Guard Interval:
Aggregation, an option where the data is grouped together for more efficient transport, and short guard interval, a reduction in the amount of “dead” time between RF communications, only have an effect when both the AP and the client are compatible, with no impact on legacy a/b/g deployments. These features can and should be employed in both Greenfield and mixed environments, and they are often something you can’t control or configure in your AP anyway. While some APs may give you the ability to enable or disable these capabilities, most decide for themselves when it’s appropriate to use aggregation and which type of aggregation (AMPDU or AMSDU) to use.
Even if you have access points that can handle this, stay away. In our opinion this feature is not ready for primetime. Beam forming allows APs to determine the approximate location of a wireless client, and then actively tune the antennas to increase signal strength in the direction of that client. This is highly complex technology, and is optional for any 11n equipment. The only time beam forming is worth considering is if you are in an outdoor environment, and you have a lot of clients in the same general direction, but even in this case it’s better to consider an AP with an antenna design that always favors the direction of the clients and does not attempt active tuning for each individual client.
Hopefully some of the mysteries were revealed. If you are interested in learning more about the complexities of 11n, check out one of WildPackets’ webinars on 802.11n.
Many super web seminars here - http://www.wildpackets.com/news_events/web_seminars
Author Bio: Jay Botelho is the Director of Product Management at WildPackets, Inc., a leading network analysis solutions provider for networks of all sizes and topologies. Jay holds an MSEE, and is an industry veteran with over 25 years of experience in product management, product marketing, program management and complex analysis. From the first mobile computers developed by GRiD Systems to modern day network infrastructure systems, Jay has been instrumental in setting corporate direction, specifying requirements for industry-leading hardware and software products, and growing product sales through targeted product marketing.