2.11g 802.11g also uses the 2.4 GHz band, but uses a robust transmission scheme called Orthogonal Frequency-Division Multiplexing (OFDM). OFDM is also used in 802.11a, but since 802.11g uses the 2.4GHz band, it has better range. 802.11g has a maximum rate of 54 Mbps, though with error correction and overhead, the aver- age speed comes out to be about 22 Mbps. There can be problems with 802.11g, since it is backward compatible with 802.11a/b. When an 802.11l device operates with an 802.11g device, the 802.11g device may slow to 802.11b speeds. 802.11n The 802.11n standard was ratified in October 2009. Yet many vendors were selling 802.11n wireless devices before then. These vendors would take what was pro- posed and sell the devices with a big 802. 11n sticker on the box. Why? Because consortium of wireless vendors got together, called themselves the WiFi Alliance, and certified devices to be 802.11n-compliant based on the 2007 draft of the 802.11n proposal. The WiFi Alliance would test devices to ensure that they would interoperate properly, hopefully saving consumers from buying wireless devices from multiple vendors that wouldn't work together. 802.1 works within both the 2.4 GHz band and the 5 GHz band. 802.11n supports 40 MHz bandwidth, which is double that of 802.11a/b/g. 802.11n also supports something called multiinput multioutput (MIMO), which supports multiplexing multiple streams to multiple antennas. These features combine to make 802.11n capable of a theoretical maximum speed of 600 Mbps, though the average Chapter 29: Wireless consumer equipment will get nowhere near that for a variety of reasons, especially in congested signal environments. In my own house, I had a wireless access point that worked fine for me, but my wife complained that the connection was slow and that her ses- sions would drop. After a year or so, I decided to take a look and see what the problem was. Hey, I'm a busy guy. Anyway, everything seemed fine configuration-wise, and I wasn't having any problems. I finally decided to fur