Because 802.11b and 802.11g share the same range, it is not necessary to perform another site survey to locate the new APs. They can be installed in the same locations that existing 802.11b APs were placed.
Although the advantage of compatibility between 802.11b and 802.11g cannot be denied, the fact that both technologies use the 2.4-GHz band poses some problems. As noted throughout this book, the 2.4-GHz band is unlicensed and is crowded. Interference can come from cordless phones, microwave ovens, and Bluetooth devices. Interference from these devices can be mitigated, but if it persists, serious problems for Wi-Fi networks can result. Because 802.11b/g networks offer only three nonoverlapping channels, there are few places to run.
Performance also takes a hit, due to the commingling of 802.11b and 802.11g. When 802.11b legacy devices use an 802.11g network, the 802.11g clients suffer from AP congestion.
Consider a conference room full of people using an AP at 54 Mbps. When the guy down the hall with the legacy 802.11b client adapter logs on to the AP, not only will the client experience 1 or 2 Mbps of throughput (simply because of the distance from the AP), but it will also absorb more of the radio's time, robbing it from other users.
In addition, to prevent 802.11g clients from getting preferential treatment over 802.11b clients, a mechanism is in place that adds bulky overhead to packets.
802.11g also uses the speedy OFDM modulation scheme; however, to support its older brother 802.11b, it must also support Complementary Code Keying, which takes a bite out of throughput.
Does this mean that 802.11b has no place in today's Wi-Fi networks? This is not the case. If you have 802.11b equipment, it can be put into low-powered devices, such as scanners or cameras. In addition, you might find some clients or groups of clients that simply don't need 54-Mbps access, and you can give them all the legacy 802.11b devices. It keeps them wirelessly connected, but you don't have to buy new equipmentat least not for a while. That said, 802.11b has a place in the network only if you have legacy 802.11b equipment sitting around and need a home for it. If you buy wireless gear, you are better off getting the 802.11g equipment, assuming you can find it for sale.
The pros of 802.11b are:
The cons of 802.11b are:
It's easy to see why 802.11g is so popular. Both the price of this high-speed, Wi-Fi solution and its compatibility with 802.11b devices make it a desirable choice, especially in environments in which both technologies are deployed.
Deploying an 802.11g solution not only makes sense for the environments over which you have control (that is, you've selected the clients and know what to expect in your WLAN), but it's also a safe way to hedge your bets in environments in which you don't know what the client adapters will use. For instance, if you offer up a hotspot at a local restaurant, 802.11g is a good choice because it's more likely that 802.11b or 802.11g will be used.
In addition, there's a comfort level for network professionals who have already lived and worked with the 2.4-GHz band. Upgrading to 802.11g is the same, easy graduation as the move from 10-Mbps Ethernet to Fast Ethernet.
Ideally, if you upgrade from 802.11b to 802.11g, your best bet is to also upgrade your clients. Although it's best to make this upgrade, it's not necessary.
The pros of 802.11g are:
The cons of 802.11g are: