|
|
 |
|||||||||||||||
|
|
|||||||||||||||
|
|||||||||||||||
|
 
|
 Making the Choice: 802.11a or 802.11g By Jim Geier
April 15, 2002
If your wireless LAN applications require high performance, then you're probably facing a decision on whether to use 802.11a or wait for 802.11g. Before making the choice, you need to fully understand what both of these standards have to offer. Let's compare and contrast these two competing technologies and then see which one best fits your needs. 802.11g 802.11g is an extension to 802.11b, the basis of the majority of wireless LANs in existence today. 802.11g will broaden 802.11b's data rates to 54 Mbps within the 2.4 GHz band using OFDM (orthogonal frequency division multiplexing) technology. Because of backward compatibility, an 802.11b radio card will interface directly with an 802.11g access point (and vice versa) at 11 Mbps or lower depending on range. You should be able to upgrade the newer 802.11b access points to be 802.11g compliant via relatively easy firmware upgrades. Range at 54 Mbps will likely be less than existing 802.11b access points operating at 11 Mbps. As a result, don't count on upgrading your existing access points that currently provide 11 Mbps throughout all areas. You'll probably need to move the access points closer together and include additional ones to accommodate higher data rates. Similar to 802.11b, 802.11g operates in the 2.4GHz band, and the transmitted signal uses approximately 30MHz, which is one third of the band. This limits the number of non-overlapping 802.11g access points to three, which is the same as 802.11b. This means that you'll have the same difficulty with 802.11g channel assignment as you do with 802.11b when covering a large area where there is a high density of users. The solution of course is to lower the power of each access point, which enables you to place access points closer. A big issue with 802.11g, which also applies to 802.11b, is considerable RF interference from other 2.4 GHz devices, such as the newer cordless phones. Companies often complain about limited wireless LAN performance when people in the facility operate cordless telephones. It possible to manage the problem by limiting sources of RF interference; however, you can't always eliminate the problem. 802.11a A big difference with 802.11a is that it operates in the 5GHz frequency band with twelve separate non-overlapping channels. As a result, you can have up to twelve access points set to different channels in the same area without them interfering with each other. This makes access point channel assignment much easier and significantly increases the throughput the wireless LAN can deliver within a given area. In addition, RF interference is much less likely because of the less-crowded 5 GHz band. Similar to 802.11g, 802.11a delivers up to 54 Mbps, with extensions to even higher data rates possible by combining channels. Due to higher frequency, however, range (around 80 feet) is somewhat less than lower frequency systems (i.e., 802.11b and 802.11g). This increases the cost of the overall system because it requires a greater number of access points, but the shorter range enables a much greater capacity in smaller areas via a higher degree of channel reuse. A huge problem with 802.11a is that it's not directly compatible with 802.11b or 802.11g networks. In other words, a user equipped with an 802.11b or 802.11g radio card will not be able to interface directly to an 802.11a access point. In applications where you have little or not control over what radio NICs, you'll run into interoperability issues. The cure for this will come eventually, however, as multimode NICs become the norm. Recommendations
To help you through this quandary, here're some tips you should consider:
Author Biography: Jim Geier provides independent consulting services to companies developing and deploying wireless network solutions. He is the author of the book, Wireless LANs (2nd Edition), and regularly instructs workshops on wireless LANs.
|
|||||||||||||||||||||||||||||||||
| Solutions | ||||||
|
||||||
|
||||||
|
||||||
|
||||||
eBook Library
IE 7
Firefox 2.0
