One from Column A, One from Column G

A guide to making sense of wireless LAN upgrade options.

Coverage, capacity and cost - these are the three main variables when deciding which version of 802.11 wireless LAN technology is right for your network. While 802.11b currently dominates the Wi-Fi market, accounting for as much as 90% of the installed base, the industry is quickly moving toward two faster standards, 802.11a and 802.11g.

Both offer nearly five times the theoretical throughput of 802.11b (54M bit/sec vs. 11M bit/sec), while promising to deliver cleaner signals with fewer dropped packets, in part because of a more advanced modulation technology, Orthogonal Frequency Division Multiplexing (OFDM). That is where the similarities end. The major benefit of 802.11g is that it operates in the same 2.4-GHz frequency band as 802.11b and has been designed for backward-compatibility. The chief benefit of 802.11a is that it operates in the relatively uncluttered 5-GHz band and offers many more channels than 802.11b/g.

To further complicate the issue, vendors are developing multi-band products that include 802.11a, b and g technology. Paul DeBeasi, vice president of marketing at Legra Systems, says, "The industry is moving toward multi-band solutions. Customers are worried about the future of their networks, and they don't want to be locked into any one standard. Especially in the enterprise, customers want multi-band flexibility, and chip vendors are beginning to deliver the silicon to meet that demand. In the near future, [network interface cards], chips and access points will all be shipping with multi-band capabilities."

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Coverage, capacity and cost - these are the three main variables when deciding which version of 802.11 wireless LAN technology is right for your network. While 802.11b currently dominates the Wi-Fi market, accounting for as much as 90% of the installed base, the industry is quickly moving toward two faster standards, 802.11a and 802.11g.

Both offer nearly five times the theoretical throughput of 802.11b (54M bit/sec vs. 11M bit/sec), while promising to deliver cleaner signals with fewer dropped packets, in part because of a more advanced modulation technology, Orthogonal Frequency Division Multiplexing (OFDM). That is where the similarities end. The major benefit of 802.11g is that it operates in the same 2.4-GHz frequency band as 802.11b and has been designed for backward-compatibility. The chief benefit of 802.11a is that it operates in the relatively uncluttered 5-GHz band and offers many more channels than 802.11b/g.

To further complicate the issue, vendors are developing multi-band products that include 802.11a, b and g technology. Paul DeBeasi, vice president of marketing at Legra Systems, says, "The industry is moving toward multi-band solutions. Customers are worried about the future of their networks, and they don't want to be locked into any one standard. Especially in the enterprise, customers want multi-band flexibility, and chip vendors are beginning to deliver the silicon to meet that demand. In the near future, [network interface cards], chips and access points will all be shipping with multi-band capabilities."

So does that mean companies don't have to make the tough choices between 802.11a and 802.11g? Not so fast, DeBeasi says. "The question then becomes one of network design. Are you designing your network for an 802.11b/g infrastructure or an 802.11a infrastructure? Or, should you design for a multi-band deployment?"

In other words, even if your network has de facto multi-mode capability, this doesn't mean it automatically supports both types of clients at once. Because a multi-band network is the most expensive option and most complicated to deploy and manage, most companies will settle on a single-band design. And that leads us back to our original question: What's best, 802.11b/g or 802.11a?

The case for G: Goes with B, gets widest coverage, great cost advantage

If cost is your main decision point, then 802.11b/g is your best bet. While 802.11b has lost market share in recent quarters, it has mostly been to 802.11g. This mean that the lower prices that result from volume productions should be shifting to 802.11g's favor.

According to Greg Collins, senior director at Dell'Oro Group, the migration from 802.11b to 802.11g accelerated in the third quarter of last year, especially in the small office/home office market. Dell'Oro found that while 60% of the access points shipped in the quarter were 802.11b, 802.11g grew from nothing a year ago to capture 39% of the market. Over time, Dell'Oro expects to see more dual-band units shipped, especially to large companies.

Operating in the lower-frequency band of 2.4 GHz, 802.11g provides a range of up to 300 feet, which is significantly better than 802.11a. The greater range translates into fewer access points for a given coverage area. Moreover, 802.11g's backward-compatibility with 802.11b protects past investments in 802.11b-only laptops and handhelds.

The fact that 802.11g operates in the same 2.4-GHz band as 802.11b is at once its greatest strength and its most glaring weakness. Sharing the 2.4-GHz band makes backward-compatibility possible, but this is a crowded band. Everything from microwave ovens to cordless phones and Bluetooth devices can interfere with an 802.11b/g signal. Worse, because 802.11b/g provides only three non-overlapping channels, when interference is encountered on one channel, there isn't much room to move.

Another key drawback of 802.11g is that supporting legacy 802.11b clients comes with a steep cost: performance degradation. To handle slower clients, 802.11g networks decrease their data rates when an 802.11b client is present, limiting access point throughput to the 11M bit/sec of 802.11b.

There is also some concern that 802.11g won't be as backward-compatible as promised. The 802.11g standard contains a protection mechanism that prevents 802.11g clients from receiving preferential treatment over slower 802.11b clients. The mechanism is bulky, adding overhead to packets, and while 802.11g uses the high-speed OFDM modulation scheme, it must also support the legacy Complementary Code Keying of 802.11b, which further degrades throughput.

To address this problem, several infrastructure vendors have begun offering the Turbo G mode in their 802.11g products. To do this, they use a technique called channel bonding, while also turning off the 802.11b protection mechanism. In essence, Turbo G leaves 802.11b clients out in the cold, while having the unintended effect of generating interference that can affect the performance of nearby access points.

Judging from these problems, you might assume that 802.11g doesn't stand a chance against 802.11a in the long term. "That's not true," DeBeasi says. "If you emphasize coverage over performance and you place a premium on good legacy support, then 802.11g will serve you well."

Insert G here

Certain environments are well suited to 802.11g. DeBeasi's company has been working with a large hotel. Serving a diverse customer base is the hotel's greatest need, and an 802.11b/g infrastructure will cost-effectively accept the broadest range of devices.

"Keep in mind," DeBeasi says, "even though from an infrastructure standpoint you typically want to choose between 802.11a and/or 802.11b/g, clients don't have that problem." With multi-mode capabilities rapidly becoming the norm on the client side, there won't be that many, if any, 802.11a-only devices entering most networks, and, thus, 802.11b/g lets you serve the broadest possible client base.

Other scenarios where 802.11g makes sense are in conference rooms or corporate lobbies. In both situations, it's impossible to know which clients will need access. Low-bandwidth applications are also good candidates for 802.11b/g, such as retail point-of-sale or inventory tracking.

According to Jeff Abramowitz, senior director of marketing for Broadcom's wireless LAN products, 802.11g is driving the Wi-Fi market. "Infrastructure is now being upgraded to 802.11g, and going forward the question becomes whether the capacity gains of 802.11a justify the additional cost." Abramowitz argues that network professionals are familiar with the 2.4-GHz band, they are looking to lower-cost products whenever possible, and they are drawn to the backward-compatibility of 802.11g.