Multimode Chips Advance Seamless Roaming

By Jim Geier

March 25, 2002

Find out how wireless roaming is being advanced by 802.11 chip set design.

One of the primary benefits of standardization is interoperability. With common standards, you can purchase a product and feel assured that it will work with other components based on the same standard. With 802.11, however, there are several flavors of the standard that are not interoperable, namely 802.11b and 802.11a.

As most of you know, 802.11b and 802.11g both operate in the 2.4GHz band; whereas, 802.11a functions in the 5GHz band. In addition, these two versions of the standard use different modulation and frame headers. As a result, 802.11b and 802.11a are not interoperable. An end user equipped with an 802.11b radio NIC can't associate with an 802.11a access point.

This is a big problem with public wireless LANs, which depend upon open connectivity to attract the widest possible number of subscribers. It's likely that some hotspots will deploy 802.11b and some will install 802.11a. In order to operate on both types of networks, users need to change their radio NIC to match the network they want to communicate with. As an example, a user may use 802.11a in their office and then need to switch to 802.11b in order to check emails at an airport. A replacement of the radio NIC such as this is too cumbersome for typical users.

A similar interoperability problem exists if a company implements 802.11b throughout a facility for general wireless connectivity and installs 802.11a in conference rooms for higher performing multimedia applications. In this case, users also need to replace their radio NIC from time-to-time in order to operate on all parts of the network. This certainly kills the idea of seamless roaming. In fact today, most IT managers are reluctant to deploy both 802.11b and 802.11a in the same facility because of the inherent lack of interoperability.

The solution: multimode 802.11
Semiconductor companies, such as Atheros and Synad, are solving the interoperability problem by including both 802.11a and 802.11b on the same chip, with mechanisms to automatically detect and change to the applicable version of the standard. This enables radio NIC and access point suppliers to feasibly implement 802.11b and 802.11a (referred to as "dual-mode") within the same radio NIC and access point. Some companies, such as Atheros, are even offering "tri-mode," which includes 802.11g in addition to 802.11a and 802.11b. Chipsets are just now being released, and the corresponding radio NICs and access points should hit the market by the end of 2002.

Multimode 802.11 will dramatically improve interoperability. A user equipped with a dual-mode radio NIC can roam freely among wireless LANs having both 802.11a and 802.11b access points. With this technology, users don't need to worry over which radio NIC to have for public access before leaving on a business trip. They'll be assured access no matter what version of the standard the wireless hotspots implement. Likewise, users within a corporation can access their email from their desk through an 802.11b network and later, without changing their radio NIC, participate in a multimedia presentation over an 802.11a connection within the conference room.

Of course multimode 802.11 doesn't totally satisfy interoperability for some of the installed base of 802.11 networks. For example, a public wireless LAN hotspot may deploy 802.11a access points, and users with the traditional 802.11b radio NICs will still not associate. Over time, however, it will be commonplace to use multimode radio NICs, similar to the use of 10/100 Mbps Ethernet NICs are today. This will get us much closer to the ubiquitous communications that everyone is talking about.

Author Biography: Jim Geier provides independent consulting services to companies developing and deploying wireless networks. He is the author of the book, Wireless LANs (2nd Edition), and regularly instructs workshops on wireless LANs.

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