Which Wi-Fi Flavor?

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IT decision-makers, at least for now, are forced to deal with multiple WLAN standards-not only those that are available today, but also those that have yet to be commercialized. The immediate problem relates to incompatibilities between the IEEE 802.11 networking specifications, e.g. 802.11b, 802.11a and 802.11g, all of which have their advocates.

We dive into the minute details behind the entire 802.11 suite of specifications in various chapters (e.g. Chapters 6, 7, and 10), but for some readers, such particulars won't be necessary for their decision-making process. So, in this chapter, we take a more myopic view of the 802.11 standards, looking at them only in the context of a corporate networking environment.

For those that don't yearn for the fast lane, 802.11b, which operates at 2.4 GHz and offers a top data transfer rate of 11 Mbps at the access point, has obvious benefits: an extremely low cost, a large installed base, and a relatively good range. The most common types of wireless LANs in operation today support the 802.11b standard.

802.1 la, however, can offer a fivefold increase in performance over 802.11b, it also operates on the less-crowded 5 GHz band (although you shouldn't put too much weight on this point), and has more channels (eight versus 11b's three). However, an 802.11a installation can be more costly than a network running 802.11b technology. And although 802.11a equipment has been available for some time, vendors of enterprise-class WLAN gear with sophisticated security and management options have only recently entered the market.

802.11g enthusiasts assert that this specification offers the best of both worlds-it runs like 802.1 la (i.e. 54 Mbps), but provides full backward compatibility with 802.11b, and more importantly provides better signal characteristics than either "a" or "b." But, because of political and technical conflicts, the 802.11g specification (the ruling document to which 802.11g products must adhere) wasn't finalized until mid-June 2003. Thus there is no installed base, which means that like all new technologies, the kinks haven't been worked out yet. Another drawback is that the specification was only newly published, thus the Wi-Fi Alliance has only recently added 802.11g as part of its certification suite.

Despite these constraints, several manufacturers (e.g. Apple, Belkin, Buffalo, and Linksys) have shipped a variety of wireless networking gear based on chipsets that use a draft version of 802.11g. But beware, any products appearing before the final 802.11g specification is ratified can only say that such products conform to a 802.11g draft specification of an underdetermined draft version. The 11g products shipped in early 2003 were designed using a mix of specification drafts that emerged from the IEEE Task Group g meetings in September 2002, November 2002, and January 2003, respectively. There are significant differences between those drafts, which can affect both 802.11b interoperability and throughput performance of draft-802.11g products.

Note 

The Wi-Fi Alliance is a nonprofit organization that tests equipment based on the 802.11 suite of specifications to ensure that the equipment is designed to work according to the specification and is interoperable with all other certified equipment. Only after the Wi-Fi Alliance's test labs give a piece of gear the "thumbs up" is the maker allowed to use the Wi-Fi logo. The great thing about the Wi-Fi certification is that interoperability of products built upon the same specification (e.g. a, b, and g) from different vendors is ensured if a product bears the "Wi-Fi" logo. Until 802.11g was finalized, however, the Wi-Fi Alliance had no way of guaranteeing that different 802.11g devices would work with one another, meaning that it will be take a bit of time after the IEEE's ratification before Wi-Fi certifified equipment hits the marketplace.

Implementing a WLAN requires that the deployment (or pilot project) team and IT department face many critical decisions, but the most important will be choosing the right wireless standard. The final decision will depend largely upon bandwidth needs and the current level of WLAN deployment within the organization.

"b" or "a"

Those struggling with the decision of whether to deploy 802.11b or 802.11a should concentrate on the value gained from the deployment, coupled with the bandwidth requirements of the applications that will run over the network. If the applications don't require bandwidth in excess of a shared 11 Mbps segment, and if it is predicted that there will be only a relatively small number of simultaneous WLAN users per access point (somewhere between 10 and 50 depending on usage patterns), 802.11b will do just fine. If more bandwidth is needed by a specific user group (e.g. marketing and its graphically intensive campaigns), the IT department can provide higher per-user throughput by reducing the number of users in each coverage area through the installation of more access points.

"b" or "a" Check List

Use this check list to help you in making a decision between an 802.11b or 802.1 la:

• An environment that has many 2.4 GHz interference sources, e.g. Bluetooth devices, wireless phones, or microwave ovens. 802.11a, which uses the 5 GHz band, may be the better choice.

• A deployment that requires more channels. A larger number of channels allows more users to share the network and protects against interference from neighboring access points. The 802.11b's 2.4 GHz band is relatively narrow, providing for just three non-overlapping frequency channels, while 802.11a offers eight channels. However, if designing an 802.11a network to harness all eight non-overlapping channels, be aware that deploying external antenna for access points is a non-option, since FCC limitations require attached antennae, fixed transmit powers, and antenna gain limits on 802.11a access points. Still, the choice to forgo some freedom in favor of all eight non-overlapping channels can be advantageous in certain deployment situations.

• Deploying a WLAN in an organization that already has an installed base of Wi-Fi equipment. The more 802.11b clients installed, the greater the need to have access points that support 802.11b.

• An organization that has a large percentage of WLAN users who also must tap into wireless networks outside the organization where 802.11b is more likely to be predominant (e.g. HotSpots, a home wireless network, or wireless access outside the U.S.). An 802.11b or a dual-mode 802.11b/a network would be the best bet.

• 802.11b is better for transaction-intensive applications; 802.11a is better for bandwidth-hungry applications.

• Budget versus costs. Provisioning an 802.1 la network usually costs 20 to 30 percent more than using 802.11b products. In addition, deploying an 802.1 la network may incur additional costs due to different RF characteristics of the 5 GHz frequency.

• Data rates and signal range. Access points offer their clients multiple data rates. For 802.11b the range is from 1 to 11 Mbps in four increments, and for 802.1 la the range is 6 to 54 Mbps in seven increments. A mobile computing device's wireless networking card will automatically switch to the fastest possible rate offered by the access point (although how different cards do it varies from vendor to vendor). Each data rate has its own unique cell of coverage (the higher the data rate, the smaller the cell), thus the minimum data rate for any given cell must be determined at the design stage. If the organization requires the WLAN to consistently provide only the highest data rate, the deployment will require a greater number of access points to cover a given area. Most network designs, however, will be a compromise between required aggregate data rate and overall system cost.

In the final analysis, the main reasons to consider deploying a WLAN based on 802.11b standards are:

• 802.11b products were the first to market, thus it is more likely to provide platform stability.

• The standard has been widely adopted by vendors and organizations alike so there is more experience with its deployment and maintenance.

• Interoperability between many of the 11b products on the market is ensured through the Wi-Fi Alliance's certification program.

• 11b's relatively high speed is more than adequate for many organizations' networking needs.

• If one of the WLAN requirements is to support a wide variety of devices from different vendors, 802.11b is probably the best choice.

• An 802.11b WLAN can be easily upgraded, usually through firmware updates, to 802.11g when advisable.

802.11a products are relatively new to the marketplace, so careful consideration should be given to their platform stability and performance. However, there are some instances when 802.1 la will win out over an 802.11b installation:

• When deploying a WLAN in a multi-story corporate environment, 11a may be the best choice because it uses smaller cells and may encounter less interference from other installations within the building.

• When higher per-user throughput is needed. 802.11a offers eight non-overlapping usable channels per access point (versus three for 11b), so when an 11a network is properly provisioned, it can provide a shared medium that offers higher per-user throughput.

The downside is that since 1 la operates at a higher frequency, it has a shorter range and requires more access points (APs) for a given coverage area than 11b. Thus, a network based on the 802.11a specification may be more expensive and may be unnecessary, especially for applications such as warehouse data entry and the typical corporate office-related applications that don't need the extra bandwidth.

"g"

Let's now look at the impact of the new 802.11g standard on the WLAN scene.

The advantage 802.11g affords is a top data rate of 54 Mbps, while maintaining full backward compatibility with 802.11b via complementary code keying (CCK) modulation. However, since 11g uses the same transmission type and modulation technique as 802.11a (i.e. OFDM) while remaining in the same 2.4 GHz spectrum as 11b, the 802.11g standard carries some range and performance characteristics from both 11b and 11a. Some of these features can limit 11g's effectiveness. Here is an example:

While 11g, like 11a, boasts a top data rate of 54 Mbps, it operates in the unlicensed portion of the 2.4 GHz spectrum, which means that the 802.11g transmissions are limited to the same three channels and crowded 2.4 GHz band as 802.11b, creating possible scalability and interference issues. Thus, although 802.11g is capable of a theoretical 54 Mbps throughput, it probably will not reach the same speeds as 11a, because of 2.4 GHz interference problems and the longer resend intervals required for backward compatibility with 11b. But, while 802.11g offers less range than 11b, it does provide greater range than 11a because of wave characteristics at the 2.4 GHz spectrum.

Furthermore, 802.11g circumvents some of 11a's FCC restrictions on auxiliary antennae and transmit power. Thus, there is more leeway in the use of creative antenna technology and deployment. Also, since 11g is compatible with 11b, the same antenna equipment from current 802.11b deployments may be used.

Organizations with a significant investment in 802.11b, but needing a performance boost without going the 802.1 la route, may want to consider 802.11g technology as long as it bears a Wi-Fi certification label. However, even though 11g's increased throughput and backward compatibility with 11b may be enticing, don't ignore the five additional non-overlapping channels you get with 11a.

As WLANs become an increasingly integral adjunct to the corporate wired network, the higher speed standards-802.11a and 802.11g-will become the logical choice because of the projected needs of future bandwidth-intensive applications (e.g. wireless videoconferencing, voice-over-wireless IP, and the like). Yet, even when 802.11b is the standard used to implement a new WLAN, you may still want to give consideration to designing the WLAN around dual-band a/b or a/g access points. By installing dual-band access points, you can not only protect existing wireless investments, but also provide a migration path to the dual-band wireless world of the future.

When taking the dual-band approach, however, a comprehensive site survey must be conducted for each specification to guarantee adequate network coverage. This is due to 802.11b's and 802.11a's different signal strength, and requirements to adjust for interference and reflection characteristics.

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