licensed frequency bands. These competing devices can cause interference for one another. Standards 802.11a and 802.11g have eight data rates: 6Mbps, 9Mbps, 12Mbps, 18Mbps, 24Mbps, 36Mbps, 48Mbps, and 54Mbps. The 6Mbps and 9Mbps modes use the BPSK modulation technique. The 12Mbps and 18Mbps modes use QPSK. The 24Mbps and 36Mbps modes use 16-QAM, and 48Mbps and 54Mbps use 64-QAM. The 802.11 systems divide the spectrum into channels, enabling multiple WAPs to operate close to each other without interference because each one can be set to a different channel. However, 802.11b and 802.11g use overlapping chan- nels. This means that in the United States and Asia, only 3 channels can be used, effectively allowing only 3 WAPs to operate without interference. In Europe, 4 channels are available. With 802.11a, the channels do not overlap, so in the United States, 12 channels are available, allowing 12 WAPs to operate in the same vicinity. In Asia, 4 channels can be used, and in Europe, 15 channels are available. Two modes of operation are specified in 802.11: infrastructure and ad hoc. In the infrastructure mode, the laptops or other wireless devices transmit to a base station, the WAP, which then connects to a wired LAN. Each WAP with its wireless devices is known as a basic service set (BSS). When there are two or more BSSs in the same subnet, it is called an extended service set (ESS). In the ad hoc mode, also called peer-to-peer mode, laptops and other wireless devices communicate directly with one another in a peer-to-peer fashion; no WAP is used. This is called an inde- pendent BSS (IBSS). Emerging 802.11 Standards: 802.11e, 802.11i, and 802.11n Three emerging standards-802.11e, 802.11i, and 802.11n-show promise in terms of addressing the deficiencies of current WLANs. The objective of IEEE 802.11e is to provide for QoS extensions to the 802.11 protocol in support of LAN applications that have QoS requirements. The 802.11e standard allows for real-time audio and video streams to be given a higher priority Chapter 15