Wireless LANs: Assuring optimal performance

Gigabit Wi-Fi might solve some of your problems, but you can probably get more out of what you already have

You're undoubtedly already thinking about that next wireless LAN upgrade, partially because BYOD and accelerating demand for mobility is straining your current installation, but also because the advent of gigabit-class wireless LANs is motivating an examination of what's working -- and what's not -- in your shop.

So even as we look forward to the newest 802.11ac systems to help address our ever-expanding needs, now is an opportune time for tuning the existing enterprise WLAN. Getting this optimization right can make a huge difference between success -- and having to work nights and weekends.

As it turns out, none of what follows is difficult -- remember, we're looking for optimal, not perfect. And the declining costs and dramatically-improving price/performance of the required systems, coupled with a reduction in operating expense thanks to greater operations-staff productivity and an overall improvement in end-user productivity (the real bottom line in any network), can easily pay for any effort involved.

Standards are just the beginning

Given the degree of functionality defined in the 802.11 standard -- roughly 3,000 pages at present -- and the remarkable capabilities of chipsets based on the standard, it's easy to assume that most of the work required in optimizing a WLAN has already been done by the IEEE and chipset vendors. It's important, however, to consider two additional complicating factors:

First, radio communications of any form is a function of the laws of physics. Radio itself is a statistical medium -- not fundamentally unreliable, but indeed subject to significant swings in performance simply as a consequence of such elements as available spectrum (channel bandwidth), the type and orientation of antennas used on both ends of a given link, interference (unintentional and otherwise), client motion and a wide variety of other variables. It's easy to see how predicting WLAN performance can be somewhere between complex and impossible.

Second, specific WLAN system implementations can have an equally dramatic impact on performance. Most enterprise-class vendors have sophisticated and often-proprietary techniques for allocating traffic to channels, prioritizing traffic and otherwise optimizing their products. It's thus advisable to learn the details of these capabilities and apply any appropriate, even if specialized, optimizations.

Defining performance goals

While we tend to think of performance in terms of throughput alone, the shared nature of the WLAN medium places a much greater emphasis on capacity -- being able to serve a large, growing and diverse (in terms of both devices and applications) user base while maintaining the overall goal of boosting end-user productivity.

The basic philosophy of WLAN deployment has, however, historically been based on coverage. This is an artifact of the time when access points were expensive, applications were primarily vertical (think logistics, transportation, warehousing and data collection) and throughput requirements were low.

Today, however, the WLAN is the primary, default or even only access for many users. Couple that with increasing demand, time-bounded traffic (voice and streaming video), the need for pervasive coverage and the environmental and vendor-proprietary variables noted above, and performance optimization is often viewed as complex or even theoretical at best.

And it gets worse. Traditional performance evaluation usually takes the form of benchmarking, involving the analysis of throughput given a quantifiable synthetic workload. While this can and does work well on wire, the inherent variability of wireless can yield unreliable conclusions unless additional steps are taken during the benchmarking process -- such elements as multiple test runs and spectral analysis are vital, given the statistically varying medium that is radio.

Assuring optimal performance: Action items

While the task may seem daunting, achieving optimal performance isn't impossible or even necessarily time-consuming. A number of basic and essential steps that any IT shop can undertake will provide a firm footing for performance optimization, as follows:

* Make sure firmware and software are up-to-date. This might seem obvious, but WLAN system vendors are making constant improvements in their systems software feature sets, and especially in their radio resource management/airtime fairness/etc. capabilities that have the potential to boost overall performance enormously. So keeping up-to-date with new releases is vital. Ditto for client drivers -- 802.11ac products will likely see frequent software and even firmware enhancements as vendors quickly run up the experience curve.

* Understand tuning options. Enterprise-class Wi-Fi systems can have literally hundreds of options and parameters that can bias performance, both positively and negatively. While many can and do affect RF transmissions, many of these features have more to do with internal scheduling than directly impacting over-the-air radio performance. Such settings as class of service, quality of service, the application of RTS/CTS and/or fragmentation, airtime fairness, channel allocation and even (or, perhaps, especially) client behavior can affect overall system performance. Keep in mind, for example, that roaming and load balancing, among other related capabilities, are largely determined by client behavior. We expect to see vendors deliver a continuing stream of innovations that compensate for these fundamental limitations in 802.11 protocols.

* Talk with your vendor. Yes, even if this means signing a confidential disclosure agreement, it's a very good idea to find out what's coming from your vendor so you can get any required resources in place in advance of installing new WLAN equipment or features. Even though over-the-air interoperability is seldom a problem in wireless LANs anymore, differentiation in system-level products has never been greater. The vendor community, without exception, continues to innovate across the board. Understanding the requirements and impacts of the next generation of these innovations -- before they go into service -- is critical to both operational success and cost control.

* Learn the management console. Surprisingly, many operations professionals are often unfamiliar with feature sets of their management console. Granted, the complexity of these facilities has multiplied over the years, and with management features today often a key competitive differentiator, even vendor vocabularies can be confusing. It is, however, absolutely critical that operations staff learn every feature of the product they are using -- seconds can count when there's a problem, and the productivity benefits of completing any action the easy way are also clear. Vendor training materials are a good place to start, but (carefully, of course) just poking around can yield an understanding that is an optimization in itself.

* Consider unified management. Speaking of management functionality, it is really no longer productive to think of, and manage, wired and wireless LANs as separate entities. While we have a wireless bias and tend to think of the wired LAN as largely serving a supporting role in the interconnection of access points, such really isn't fair. Each domain has its own set of policies and optimizations, and these must operate in concert for optimal network performance. We're starting to see much more capable unified management platforms today, and, depending upon your equipment base, these are more than worth exploring. Again, this is a subject for a discussion with your vendor. Multivendor operations and especially software-defined networking (SDN) might also be on the agenda for this conversation as well -- we're expecting SDN to be a major influence on network architecture, design, implementation and management going forward -- again, wired and wireless.

* Optimize for capacity, not coverage. Given the high cost and very limited performance of pre-standard WLAN gear, the early days of wireless LANs almost always involved a site survey to determine the "best" location for each access point. Give the high performance and low cost of today's systems, however, far too many organizations are still doing expensive, labor-intensive pre-installation site surveys. A better approach is to examine where capacity is needed, deploy appropriate AP density (keep in mind that WLAN performance is all about rate vs. range, with rate improving as range decreases), and then do a quick post-installation site survey verifying performance and locating any holes in coverage or capacity that can be easily remedied at minimal cost via the installation of additional APs. Given the non-linearities of RF propagation and shifting location-based demand patterns over time, we have another good reason to learn the performance-related capabilities of the management console, with frequent checks on actual performance.

A pre-installation site survey may be indicated in unusual environments (we once did one in a nuclear power plant), and an RF sweep with a spectrum analyzer is also a good idea from time to time to ferret out potential interferers.

* Establish an assurance strategy. Ultimately, optimal WLAN services are dependent upon continual monitoring and performance analysis -- in other words, being proactive rather than reactive. This is the domain of WLAN assurance systems, which, depending upon implementation, can include such diverse functions as intrusion detection and prevention (IDS/IPS), rogue AP detection and mitigation, compliance reporting, automated diagnostics, and much more.

Assurance systems are based on a network of sensors that can cover significant range, as they are receivers only. The big question is whether to install an assurance system separate from the wireless LAN, or to obtain this functionality from a WLAN system vendor. An excellent argument can be made for a separate, independent system if full-time monitoring is required or multiple WLAN vendors are involved, and such assurance products tends to have a broader range of function regardless. Laptop-based and even handheld tools are also available here -- assurance products that address every need from small shop to global are broadly available.

Given the high degree of variability, again based in the fundamental laws of physics and inherent in wireless communications of any form, there will always be the occasional performance or related challenge interrupting the day of network operations professionals. As we've discussed above, however, a few simple steps can, to a very great degree, yield optimal productivity for operations staff and, especially, end users alike.

The Farpoint Group is an advisory firm specializing in wireless networking and mobile computing. Founded in 1991, Farpoint Group works with technology developers, manufacturers, carriers and operators, enterprises and the financial community. Craig is an internationally recognized industry and technology analyst, consultant, conference speaker and author, and is the writer of the Nearpoints blog. He is also the chairman of the Mobility track at the Interop conferences. Craig holds a bachelor's degree in computer science from Brown University, and is a member of the IEEE and the Society of Sigma Xi.

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