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The "G" Versus "A" WLAN Conundrum


Lower prices and killer apps such as voice-over-WLAN (VoWLAN) are the main reasons wireless networks are proliferating in enterprises. VoWLANs, for instance can save enterprises loads of money while enabling mobile telephony throughout a facility.

But these applications beg the question: Is use of 802.11g, by far the most widely-deployed WLAN standard, sufficient or should IT managers add 802.11a as well?

Many companies automatically choose 802.11g because it's compatible with the older 802.11b equipment. But if you take a close look, you may find that 802.11a may make the most sense to deploy either alone or in tandem with 802.11g.

How They Are They Similar

Both 802.11a and 802.11g operate at up to 54Mbps data rates, which is actually the speed that the bits of an 802.11 frame, such as a beacon, data, and acknowledgement, are sent over the air. Because of similar data rates, they appear to have equal performance. However, keep in mind that data rate isn't necessarily a good measure of the performance that users will actually experience.

With 802.11 systems, transmission delays are created because of other user traffic is sharing the same channel, the presence of RF interference and the enabling of various configuration settings, such as power management and fragmentation. For example, a wireless mobile device may transmit frames at 48Mbps, but very poor throughput may prevail if the user is operating close to a microwave oven that uses the same chunk of spectrum or if the immediate area is full of wireless users operating VoWLAN phones associated with the same access point.

802.11a and 802.11g use common 802.11 medium access control (MAC) layer functions. As a result, protocols responsible for operation of the network, including security, power management and fragmentation, are essentially the same. 802.11a and 802.11g only implement physical layer functions, such as modulation and demodulation, not the higher layer stuff.

Generally, 802.11a and 802.11g are sold as separate adapters. Some adapters are available, however, that vendors refer to as multi-mode or multi-band, which implements 802.11a and 802.11g together in the same card. Most user devices today are not equipped with multi-band cards, but they will likely become commonplace in the future.