What is Wi-Fi?
Modern networking has slowly come of age, replacing wired interfaces with wireless connections governed by IEEE 802.11 standards. 802.11 communications function the same as wired connections, with the OSI physical layer moving from a hard wired connection to wireless broadcast and the OSI data link layer using the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol to regulate the transmissions of data. CSMA/CA, to prevent packet collision, listens to a channel for a predetermined amount of time to see if the channel is in use. If the channel is determined to be idle, the node is allowed to start broadcasting.
Some of the early 802.11 standards, 802.11a, set forth rules of wireless operation in the 5GHz range supporting data transmission upwards of 54Mbit/second. (With error correction, maximum practical attainable data transmission was around 27Mbit/s). 802.11a used OFDM, Orthogonal Frequency Division Multiplexing, dividing the data to be transmitted up over 52 subcarriers in the 5GHz range. This broadcast method is called broadcasting in parallel. One of 802.11a major drawback was range when compared to 802.11b; maximum transmission distances reaching 60 feet.
802.11b, ratified in 1999, operates in the 2.4GHz radio frequency band. It can attain data transmission speeds of up to 11Mbit/s and has a theoretical range of 300 feet. Unlike the OFDM of the 802.11a, the broadcast of 802.11b was controlled by DSSS or Direct Sequence Spread Spectrum. DSSS, OSI layer 1, sequences the data across any one or multiple 22MHz band in the 2.4GHz set.
In June of 2003, 802.11g was ratified. 802.11g was the third Wi-Fi standard ratified after 802.11a and b. It functions on the 2.4GHz range like 802.11b but uses ODFM like 802.11a to attain speeds of 54Mbit/s. 802.11g can optionally use DSSS for backwards compatibility with 802.11b. The range of 802.11g is slightly less than that of 802.11b, theoretically broadcasting upwards of 300 feet.
Used in draft form since 2007 and becoming a standard in 2009, 802.11n uses a little from all of the above. 802.11n operates in both the 2.4GHz and 5.0GHz ranges. For higher throughput it added MIMO (Multiple-Input Multiple-Output) antennas to the package. The theoretical transmission rate with 802.11n was up to 600Mbit/s, 150Mbit/s across 4 channels. It, too, uses OFDM to distribute data across multiple carrier frequencies.