The 802.11g standard is still in draft form, but understanding its impact on the WLAN scene is a must for wireless administrators. Some feel that 802.11a will be obsolesced quickly by the backward-compatible 802.11g, while others say 802.11a's positive traits heavily outweigh 802.11g's pros. The debate has begun and won't be settled soon. Here's a primer for administrators in need of high-performance WLAN technologies.
To put it plainly, the advantage 802.11g affords is an increase in speed while maintaining backward compatibility with 802.11b. Operating in the same 2.4-GHz spectrum as 802.11b, 802.11g uses the OFDM (Orthogonal Frequency Division Multiplexing) transmission type that 802.11a uses, while also supporting the DSSS (Direct-Sequence Spread-Spectrum) transmission type 802.11b uses. Combining these two transmission types lets 802.11b and 802.11g clients co-exist on the same wireless network while theoretically enabling 802.11g to reach speeds equal to 802.11a.
By using the same transmission type and modulation as 802.11a, while remaining in the 2.4-GHz spectrum, 802.11g carries some range and performance characteristics from both 802.11b and 802.11a. Although 802.11g is capable of a theoretical 54-Mbps throughput, it likely will not reach the same speeds as 802.11a (we've seen averages around 16.5 Mbps in prestandard products) because of 2.4-GHz interference problems and the longer resend intervals required for backward compatibility with 802.11b. On the plus side, ranges well above 802.11a (but decidedly less than 802.11b) are expected because of wave characteristics at the 2.4-GHz spectrum.
The choice to deploy 802.11g is also not nearly as cut and dried as some may think. Administrators with 802.11a experience know that external antennas are a nonoption for APs that harness all eight nonoverlapping channels (FCC limitations require attached antennas, fixed transmit powers and antenna-gain limits on APs that allow use of the lower four nonoverlapping channels). The choice to forgo some freedom in favor of all eight nonoverlapping channels is to administrators' advantage with 802.11a because deployment is greatly eased as more nonoverlapping channels become available. 802.11g, however, continues to use the same three nonoverlapping channels characteristic of 802.11b, perpetuating the deployment issues extant with those installations.
802.11g circumvents some of the FCC restrictions levied on 802.11a, letting administrators use auxiliary antennas and adjust transmit power. Also, because of 802.11g's compatibility with 802.11b, the same antenna equipment may be used from current 802.11b deployments.
Those interested in supporting clients of both technologies should consider dual APs that, either off-the-shelf or through field upgrades, support both 802.11a and 802.11g, but choosing to deploy one or the other isn't as simple. While 802.11g's increased throughput and backward compatibility with 802.11b may be enticing, administrators interested in high-performance WLANs simply cannot ignore 802.11a's drastic difference in speed and the standard's five additional nonoverlapping channels. --Jesse Lindeman
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