In our last blog post, we reviewed the definitions and performance benefits of the new features in 802.11n. Even with the definitions and brief technical descriptions of these capabilities, there still remains a very important yet unanswered question:
Will these upgrades affect me negatively or positively?
Some of the upgrades can be very beneficial to your wireless service delivery, but it depends on what environment you are working in. If you are deploying in a Greenfield environment, meaning you are starting your wireless project from scratch, you can take advantage of more of these upgrades as compared to deploying in a mixed environment. In a mixed environment, you already have a wireless LAN in place and are utilizing 802.11a/b/g technology, which introduces the possibility of negative effects from some of these new features.
With this filter in mind, let’s dissect how employing each feature differs depending on your environment and what 11n equipment is available to you.
2-Stream, 3-Stream, or 4-Stream (MIMO):
802.11n allows the transmission of up to 4 unique streams of data simultaneously between APs and clients – but note, although the technology allows 4-streams, there are not many commercial APs on the market that can handle this, and even fewer wireless adapters for clients. Adding these data streams increases the overall throughput, but only between compatible APs and clients, and only up to the level of the less feature-rich device.
When working within a mixed environment it is essential to keep in mind the capabilities of all of your users. Since MIMO-enabled APs are backward compatible, it makes sense to deploy APs that will provide adequate performance both today and in the future – that’s 3-stream APs today. However, if you’re not planning on upgrading all of your clients to 3-stream, then be careful on how you “market” the new capability to the organization. Once users hear that the APs are capable of 450Mbps, they will expect that level of performance, but if they’re using a laptop that’s still 802.11g, or even 11n Draft v2.0 (2-stream at best) they will continue to see data rates far below the maximum 450Mbps data rate for 3-stream devices.
As for Greenfield environments, assuming everyone is getting new gear, a full 3-stream roll-out seems like the way to go. Occasionally, you might get a visitor or remote employee with a 2-stream device, but the technology is backward compatible so these users will still be able to connect to your network – they’ll just experience slower data rates.
The upside of channel bonding in 802.11n is that it’s been available in most 11n equipment shipped since the Draft v2.0 11n standard was in place, and requires only a simple configuration change to reap the benefits. However, if you are working in a mixed environment, channel bonding can reduce the number of available channels for legacy 802.11a/b/g equipment, and it can negatively affect your entire wireless LAN and overall data throughput. This is especially true in the 2.4GHz band (the b/g channels 1 – 11 in the US), where the channel spacing is only 5MHz and co-channel interference is already a problem. Channel bonding requires an additional 20MHz of bandwidth, essentially occupying an additional 4 channels, and using far more than 50% of the total available bandwidth in the entire 2.4Ghz range for a single AP. If channel bonding is to be used in a mixed environment, restrict its usage to the 5GHz band where the 10MHz channel spacing reduces the severity of the interference problem.
If you are deploying in a Greenfield environment, this option is more advantageous. Just keep in mind that you might be interfering with your neighbors who are using 802.11a/b/g equipment. The perfect place to use this technology is a large campus that has few or no neighbors, as opposed to an office with many neighbors. Also, this capability will see a huge advancement with the advent of 11ac, which allows for wider channel access and less interference.
Aggregation (A-MPDU/A-MSDU) and Short Guard Interval:
For both mixed and Greenfield environments, these technologies are definitely worth taking advantage of, and they are often something you can’t control or configure in your AP anyway.
As stated in our last post, this is something that should be avoided, as it is not quite ready for primetime. Even if you are in an outdoor environment and you have multiple clients in the same general direction, it is still better to use an AP with an antenna design that favors the direction of the clients and does not attempt active tuning for each individual client like in beam forming.
Current Commercially Available 11n Equipment:
There are a lot of 3×3 (three transmit antennas and three receive antennas) wireless adapters and APs on the market, however these devices do not necessarily provide 3-stream throughput. If the 3×3 device you are considering advertises a maximum data rate of 300MBps, it is not 3-stream capable, and cannot be made compatible with a simple firmware update. Be sure to look for wireless adapters and APs that have 3×3:3 capabilities (with the “:3” representing the number of streams), or, because this is often not listed on the packaging, look for devices that advertise 450Mbps of throughput. And keep in mind that 3-stream APs are more common than 3-stream wireless adapters in today’s market.
If you go to the WiFi alliance website, you can search for all the certified products that are 11n capable. You can’t do a specific search for 3-stream capabilities, so you’ll need to comb through the search results to see if the devices are 11n and 3-stream capable. To have the best chance of finding 3-stream devices on the website, look for devices that were certified in 2011, and look at the certificate for each device which clearly lists the number of streams tested.
If you want to learn more about what upgrades you should be looking at when deploying 11n, check out this short video clip that goes into details for each capability and outlines what is best for your company.