 about which we have more poised for major commercial successes and widespread to say in section 5.1.3.8. Task group "F" is responsible for deployment. Sales volumes grew rapidly, and prices for providing the missing description of the distribution CHAPTER 5.1 Wireless local area networks system functions, SO that roaming between access points Let us first examine CCK. CCK is a block code: chunks can be supported across any compliant vendor's prod- of symbols of fixed size are used as code words, and the ucts; an IAPP specification was approved in June 2003. subset of allowed code words is much smaller than the Recall that the original Ethernet standard, and the total possible set of code words. Errors are detected and 802.11 MAC derived from it, deliver best-effort data corrected by comparing the received code word with the services, with no guarantees of how long the delivery possible code words: if the received code word is not an will take. Services such as voice or real-time video de- allowed word but is close to an allowed word, one may livery require not only that data be delivered but that it with good confidence assume that the nearby allowed arrive at the destination within a specified time window. code word is in fact what was transmitted. Block codes This requirement is commonly placed under the not- are relatively easy to implement. very-informative moniker of quality of service. Task We look at the high-rate 11 Mbps coding in detail. group "E" is defining quality of service standards for In the particular code used in the 802.11b CCK- time-sensitive traffic over 802.11 networks, although to 11 Mbps option, transmitted QPSK symbols are grouped some extent that effort has refocused on the 802.15 into blocks of eight to form code words. Because each work we describe in the next section. Task group "H" is symbol carries 2 bits, there are 48 = 65,536 possible defining two important additions to the 802.11 stan- code words. Of this large domain, only 256 code dard: dynamic frequency selection and transmit