-Fi consumes far more power than cellular. The Wi-Fi standards define a power-saving mode, but using it is not an optimum solution because it requires that the handset wake up to receive beacon messages from the WAP several times per second to see if any traffic is awaiting delivery. Vendors are developing more efficient power-saving schemes and are proposing them to standards bodies. Security continues to be one of the major issues affecting the use of WLANs, particularly in commercial organizations. The fact that radio signals propagate through free space, combined with the very limited security features associated with 802.11b, creates a major security concern for large enterprises as well as small offices and home businesses. Fortunately, there have been several important enhancements to WLAN security standards, such as WPA2 and 802.11i (as dis- cussed earlier in this chapter). Another important area of functionality has to do with seamless handoffs- that is, the ability to hand off a call from the cellular network to a WLAN, or vice versa. This is particularly vital to voice calls, where handoffs are much more likely to be required because the user's mobility is greater. Handoffs are SO important that the emerging standard IEEE 802.21 addresses them. This standard is designed to enable seamless handoffs between networks of the same type as well as handoffs between different network types, such as cellular, GSM, GPRS, 802.11 networks, and Bluetooth. Another emerging area that addresses the need to move between networks is cognitive radio (discussed in Chapter 16), which is a smart wireless WLANs technology that will serve the user by first locating and then connecting with any nearby open radio frequency. Finally, feature integration is a highly desirable part of dual-network (i.e., WLAN and cellular) functionality. The goal of integrating 802.11 technology within the enterprise with cellular telephony outside the enterprise is to simplify business communications and support contiguous communications across n