than 100 milliseconds. However, these initial offerings have shortcomings. For instance, there are different sets of features on WLAN and cellular calls. Also, not all cellular calls are automatically transferred to the WLAN when the user gets within range. These shortcomings are to be addressed in future releases. Meanwhile, two major questions have been at issue in the integration of WLANs and cellular: Can WLANs support voice effectively? Do cellular carriers have any real desire, or incentive, to support VoWLAN? The following sections dis- cuss these issues. Chapter 15 WMANs, WLANs, and WPANs Technology Issues for Integrating WLANs and Cellular Networks The main concerns in using a WLAN to support voice include network capacity and traffic prioritization, battery life, security, handoffs, and feature integration. The recently announced systems address these concerns by implementing WPA, proprietary architectures, and proprietary approaches to feature access. The issues of network capacity and traffic prioritization present a rather diffi- cult problem, due to the limitations of using a shared-media LAN. These concerns are being addressed by providing handsets that support the three major radio link standards, 802.11a, 802.11b, and 802.11g. IEEE 802.1 and g, operating over the .4GHz band, provide only 3 noninterfering channels, leaving them open to inter- ference from cordless phones, microwave ovens, baby monitors, and neighbors' WLANs. IEEE 802.11a, operating in the 5GHz band, provides 12 channels, 8 dedi- cated to indoor and 4 dedicated to point-to-point. However, given the higher- frequency band, 5GHz, more WAPs are required to cover an area. By using .729 compression, vendors currently claim that they can handle 8 voice calls on an 802.11b WLAN channel and 20 on an 802.11a or 802.11g channel, while using some 50% of a WLAN's capacity. However, because there are few large-scale voice installations in place, it is difficult to verify these claims. Battery life is a critical element in all mobile devices. Wi