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While all the major enterprise-grade wireless LAN access providers now support 802.11n, one of the many stumbling blocks for enterprises interested in pursuing the technology is the current lack of adequate planning and troubleshooting tools to help ease the migration from legacy WLAN standards.
So far, portable and overlay wireless analysis tools have supported 802.11n only in a limited fashion.
These products have been able to detect the presence of devices operating in draft 802.11n or pre-N modes, and perhaps detect the use of 40MHz wide channels. However, these tools have not been able to take on the 11n data or management frame analysis required to actually troubleshoot 802.11n networks. What’s more, this generation of tools has not been able to locate accurately the position of 11n devices operating in HT (high throughput) mode.
eWEEK Labs evaluates wireless LAN tools. Read the review.
Fortunately, satisfactory 802.11n support for both portable analyzers and overlay analysis and security networks is on its way. I anticipate that several wireless networking players will announce full 802.11n analysis support for their products, starting at the Interop show in Las Vegas later this month and continuing throughout the rest of the second quarter.
With a herd of new 802.11n analysis tool product refreshes on the horizon, wireless administrators should begin to familiarize themselves with some of the more technical aspects of 802.11n to best compare these vendors’ offerings. After all, not every vendor will come out of the gate with the same features and functions.
How 802.11n Changes the Game
How 802.11n Changes the Game
For wireless analysis and planning tools, extending support to include 802.11n is not just a matter of tossing an N-enabled sensor into an overlay network or of supporting an N-enabled client driver for a portable analyzer. 802.11n introduces a number of profound technology changes to the WLAN standard that will require significant product overhauls.
As Chris Roeckl, AirMagnet’s vice president of marketing, explained it: “There is a huge delta between how the current technologies work and what will happen with 802.11n. 802.11n changes virtually all the rules. Our job is to solve that problem for people and make it simple to implement this new technology.”
The changes that 802.11n brings are reflected in both the PHY (physical) and MAC (media access control) layers, and while these changes combine to dramatically boost overall throughput performance of an 802.11n wireless network, they also put a kink in the planning and analysis schemes that these products employ.
For an excellent overview of the technology changes that 802.11n brings, check out the AirMagnet Web-inar, “802.11n Primer: What You Need to Know,” which is available at airmagnet.com/news/webinars/archived (registration required).
While there are numerous enhancements in 802.11n when compared with legacy standards, there are a handful of new features that most directly impact analysis tools. These new features include: the use of MIMO (multiple input, multiple output); the use of wide (40MHz) channels that boost the number of possible subcarriers and modulation rates; the introduction of beamforming for extending range and reducing interference and the use of frame aggregation techniques that maximize the amount of data frames transmitted while simultaneously reducing the amount of over-the-air management traffic.
Good 802.11n analysis tools should provide insight into each of these characteristics to help administrators troubleshoot their speedy new wireless networks.
Analysis Tools
MIMO, a technology that leverages multipath reflection to simultaneously send different data over multiple paths, will necessitate a broad set of changes in analysis tools. For instance, access point placement will likely be different for 802.11n networks as opposed to legacy APs, as 802.11n devices may experience better behavior in places legacy devices struggled.
“We are discovering some of the assumptions we have for 802.11abg don’t apply to 11n,” said Manish Rai, Motorola’s director of product marketing for enterprise WLANs. “11n works really well in multipath-rich environments because of the MIMO technology. You get more reflections that actually improve performance.”
In particular, survey tools are going to need much more flexibility in their predictive capabilities to deal with the changes in the 802.11n PHY that come with MIMO. The tools will need to take into account antenna configurations, for instance, allowing the administrator to simulate the effects of an 802.11n AP running with 2-by-2 (2 transmit with 2 receive), 2-by-3 or 3-by-3 modes.
Likewise, location-tracking analysis systems will require extensive changes to their predictive placement algorithms because multipath propagation will provide conflicting information to sensors on where a device may be.
Wider Range of Rates
Wider Range of Rates
The available data rates offered by 802.11n networks, which now extend all the way up to 300M bps (or up to 600M bps in future 4-by-4 antenna implementations), are determined by several factors: the number of simultaneous streams, the width of the WLAN channel and the length of the guard interval (a waiting period built into the standard to avoid echo effects, which has been shortened for 802.11n).
802.11n analysis tools will need to identify not only the data rates advertised for an 802.11n WLAN but also the reasons why those particular rates are available, in order to help administrators identify possible mis-configurations in the new standard’s wide variety of tunable knobs.
Beamforming
Beamforming-an optional feature of 802.11n under which APs dynamically switch antenna combinations to focus wireless transmissions on a particular wireless client to maximize reception for that station-will also cause headaches for wireless administrators.
Current models for overlay networks fail to provide accurate coverage information in a network using beamforming.
A stationary WLAN sensor will struggle to accurately predict client coverage in this sort of network because the AP’s antennae are not pointing at the sensor. Combating this problem will be tough, as vendors will need to include either client-side analysis (requiring some kind of agent on all WLAN
clients) or denser wireless sensor deployments. The latter scenario seems untenable because 802.11n is often billed as a way to lessen the number of sensors deployed in an enterprise due to the technology’s improved performance at longer distances.
Frame Aggregation
Normal WLAN activity includes a lot of management frames, and this is why throughput totals reported in tests are significantly less than the advertised data rate. 802.11n introduces two flavors of frame aggregation-8KB MAC Service Data Unit Aggregation and the 65KB MAC Protocol Data Unit Aggregation-both of which allow for more data to be sent over the air with less management overhead.
802.11n-enabled analysis tools should be able to clearly identify when frame aggregation is in use and which type is being employed-as each type has different rules surrounding re-transmits if the packets are damaged. ??
eWEEK Labs Senior Analyst Andrew Garcia can be reached at [email protected].