802.11 Alphabet Soup - Page 2

By Jim Geier

August 05, 2002

802.11g - Higher Rate Extensions in the 2.4GHz Band

The charter of the 802.11g task group is to develop a higher speed extension (up to 54Mbps) to the 802.11b PHY, while operating in the 2.4GHz band. 802.11g will implement all mandatory elements of the IEEE 802.11b PHY standard. For example, an 802.11b user will be able to associate with an 802.11b access point and operate at data rates up to 11Mbps. In early 2002, 802.11g decided to use OFDM instead of DSSS as the basis for providing the higher data rate extensions.

An issue is that the presence of an 802.11b user on an 802.11g network will require the use of RTS / CTS (request-to-send / clear-to-send), which generates substantial overhead and lowers throughput significantly for all 802.11b and 802.11g users. RTS / CTS ensures that the sending station first transmit a RTS frame and receive a CTS frame from the access point before sending data. A mixture of 802.11b and 802.11g requires RTS / CTS to avoid collisions because 802.11b stations can't hear 802.11g stations using OFDM.

It's unclear at this date when 802.11g will ratify the standard. In addition, the FCC (Federal Communications Commission) still needs to approve the use of OFDM in the 2.4GHz band, a generally necessary action when messing with the PHY. As a result, it will likely take a relatively long period of time before 802.11g products appear on the market.

There's been much debate over the use of 802.11g vs. 802.11a for satisfying needs for higher performance WLAN applications. For the foreseeable future, your only selection for data rates beyond 802.11b's 11Mbps is to use 802.11a. Because of the earlier time to market and superior performance capacity, 802.11a will likely dominate the high performance WLAN market in the near-term and distant future.

802.11h - Spectrum Managed 802.11a

802.11h addresses the requirements of the European regulatory bodies. It provide dynamic channel selection (DCS) and transmit power control (TPC) for devices operating in the 5GHz band (802.11a). In Europe, there's a strong potential for 802.11a interfering with satellite communications, which have "primary use" designations. Most countries authorize WLANs for "secondary use" only. Through the use of DCS and TPC, 802.11h will avoid interference in a way similar to HiperLAN/2, the European-based competitor to 802.11a. 802.11h hopes to have their standard finalized sometime before the end of 2003.

To implement DCS and TPC, 802.11h is developing associated practices that affect both the MAC and PHY Layers. The inclusion of DCS and TPC will likely enable 802.11h to become the successor to 802.11a. Fortunately, there shouldn't be any issues of non-interoperability between existing 802.11a and 802.11h users and access points. The good news is that 802.11h is enabling sales of 802.11a networks in Europe, which will eventually result in higher sales volumes and lower prices.

802.11i - MAC Enhancements for Enhanced Security

802.11i is actively defining enhancements to the MAC Layer to counter the issues related to wired equivalent privacy (WEP). The existing 802.11 standard specifies the use of relatively weak, static encryption keys without any form of key distribution management. This makes it possible for hackers to access and decipher WEP-encrypted data on your WLAN. 802.11i will incorporate 802.1x and stronger encryption techniques, such as AES (Advanced Encryption Standard). In a previous tutorial, I discuss more details of how 802.11i is beefing up security.

Don't expect 802.11i to be available in the near future. The standard will likely not have IEEE ratification before mid-2003. 802.11i updates the MAC Layer, so you should be able to upgrade existing access points with firmware upgrades. The implementation of AES, however, may require new hardware.

For now, you can obtain stronger forms of security that go well beyond WEP by implementing proprietary security mechanisms available from access points vendors. The problem is that you'll probably need to deploy network cards and access points from the same vendor. As a minimum, utilize WEP.

802.11 Next Generation

In addition to the above task groups, the 802.11 WG is studying new methods to increase performance and make better use of the radio spectrum. For example, the group is considering the use of ultrawideband modulation as a new mechanism for supporting higher speed applications and reducing the potential for RF interference. You won't see these newer, faster standards for a number of years, though.

Jim Geier provides independent consulting services to companies developing and deploying wireless network solutions. He is the author of the book, Wireless LANs (SAMs, 2001), and regularly instructs workshops on wireless LANs.

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