802.11 Wireless Networks: The Definitive Guide, 2nd Edition

Chapter 14. 802.11g: The Extended-Rate PHY (ERP)

When wireless LANs first entered the mainstream computing consciousness, there was one practical choice. 802.11b had recently been standardized, and offered the prospect of near-Ethernet speed, which, to be fair, by that point was not very fast at all. As 802.11a emerged from the laboratory into commercially-available chipsets, users had a desire to obtain higher speeds than 802.11b, while retaining backwards compatibility with the installed base of 802.11b hardware. The result is 802.11g, which offers a headline bit rate comparable to 802.11a while still operating in the microwave band. By working at slightly less than half the frequency, 802.11g devices have better range than the 5 GHz 802.11a devices.

802.11g is not a revolutionary specification. In fact, if you read the new clauses added by the specification, it is clear that it uses much of the existing work done elsewhere. The new physical layers it specifies are built on existing work, and there are only slight modifications. Most of 802.11g is occupied with providing backwards compatibility.

802.11g Components

802.11g is really several physical layer specifications in one. It adds one umbrella clause for the Extended Rate PHY (ERP). However, there are several different “flavors” of ERP:

ERP-DSSS and ERP-CCK

These modes are backwards compatible with the original direct sequence specification (1 Mbps and 2 Mbps) described in Chapter 11, as well as the 802.11b enhancements (5.5 Mbps ...