April 9, 2010

802.11n Primer

In less than a decade, wireless LANs have evolved from a niche technology useable only by a few specialized applications to the default media of choice for millions of businesses and consumers. And WLANs continue to evolve. The latest generation of high-speed wireless LAN technology, based on the Institute of Electrical and Electronics Engineers (IEEE) Draft 802.11n standard, are now becoming available.

The technology behind 802.11n is projected to deliver as much as a six fold increase in effective bandwidth, as well as increased WLAN reliability compared to existing 802.11g and 802.11a deployments. The promise of 802.11n has led some to consider the wireless LAN as a viable alternative to the wired network.

At a minimum, the advances realized by 802.11n will cause many enterprises to reconsider the role of WLANs in their network, as well as the effect of such a deployment on their infrastructure. Before deploying 802.11n, however, organizations will need to understand the answers to some basic questions, including:
  • What do 802.11n technologies do differently than existing WLAN elements?
  • Is 802.11n backward-compatible with my existing wired and wireless network design?
  • What modes can the deployed?

While these questions are simple, the answers to them are not. 802.11n utilizes some very complex technologies, some more frequently used in the worlds of radio/broadcast than in networking. Indeed, there is no shortage of white papers claiming to "demystify" 802.11n but only succeeding in introducing a plethora of new four letter acronyms.

In this paper, we will look at the basic elements of 802.11n functionality, with an emphasis on how it differs from WLAN technologies in use today. Our primary focus will be on the major methods that 802.11n uses to deliver on the claim of large increases in throughput and reliability.

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This is a superb addition to our library. In particular, the paper does a fantastic job of comparing 802.11n with its predecessors and explaining why 11n is such a significant improvement.

I am especially impressed with the straight-forward explanations of MIMO and channel bonding and why these are such significant improvements.

It seems from the paper as if there are significant technical advantages to moving to an 11n-only environment. However, there are a lot of common devices still being manufactured (such as the iPod Touch and some netbooks) that only support 11b/g.

What do you see as a best compromise between maximum performance and support for the widest range of devices? Should one ever consider implementing two overly nets, one for legacy support and another for 11n?

Certainly 11n is always the best solution for APs. The simple answer to this is that 11n makes a better AP for a/b/g clients than a/b/g APs and given that 11n APs are the same cost as 11a/b/g APs, there is no reason to install a dedicated a/b/g network.

That said, what you say about an overlay network has some merit, and in fact is the recommended way to deploy. The vast majority of 11n APs sold are of the two radio type, with one radio operating in 2.4 GHz (b/g/n) and one operating in 5 GHz (a/n). A best practice for networks that have lots of legacy clients is to allow them to connect to 2.4 GHz and preserve 5GHz for 11n. This essentially gives you an overlay network for legacy clients without having to deploy 2 networks.

So, with any network, there's never enough speed and the demand grows exponentially.

What do you see beyond 11n? Should we make a big push in making everything 11n compatible, or should we do minimal 11n implementation while awaiting the next improvement?

Well, this is one of those lucky times you don't have to depend on my "vision." The industry has recognized this and has several new varieties of WiFi on the way.

The first is faster versions of 11n, this includes 3 and 4 spacial stream 11n (we currently use 2). This improves 11n's data rate per radio from 300 Mbps, to 450 or 600 Mbps. While this is not an exponential increase in throughput, it does provide for slight improvements based on existing technology. 3 spacial streams for enterprise products will be available in the coming year. 4 spacial streams may never make it to the enterprise because it may be preempted by the next wireless standard...

802.11ac is the next generation wireless standard which will offer gigabit level performance. This is still a few years out, but gives wireless networks the next kick in performance.

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