ough a carrier or through a reseller, customers are connected to a prepaid platform, which authenticates their device and tracks usage to determine either whether to charge a credit card or if the subscriber's amount of time or usage has been used up. The prepaid platform is connected to the carrier's core mobile network. Wal-Mart sells prepaid services using Straight Talk's prepaid platform. WI-FI STANDARDS, ARCHITECTURE, AND THEIR USE IN CELLULAR NETWORKS Residential consumers and enterprise staff expect the same level of mobility within homes and work environments as they experience in mobile cellular networks such as those operated by Verizon Wireless and AT&T Mobility. Wi-Fi provides short-range wireless service within these locations. Wi-Fi networks are widely deployed in cafes, libraries, and municipalities as a service to customers and city and town residents. The 802.11 Wi-Fi Standard The designation 802.11 refers to the family of Institute of Electrical and Electronics Engineers (IEEE) standards around which most Wireless Local Area Networks are built. Wi-Fi, short for wireless fidelity, is widely accepted worldwide with small variations. Table 7-4 lists the earliest commonly installed 802.11 network protocols. Table 7-4 802.11 Wireless Local Area Network (Wi-Fi) Standards Achievable Number of Frequency Speed Speed Channels* www.TechnicalPDF.com 802.11a 54Mbps 25Mbps 802.11b 11Mbps 5Mbps 2.4GHz 802.11g 54Mbps 12- to 25Mbps 2.4GHz *The number of channels varies internationally. A Deeper Dive into Wi-Fi Standards The standards presented in Table 7-3 refer to the frequencies, speeds, and number of channels in each Wi- Fi standard. Other 802.11 standards that specify capabilities such as security, Quality of Service (QoS), and internetworking with cellular networks are listed in Table 7-8 in the "Appendix" section at the end of this chapter. Wi-Fi networks in enterprises commonly support all three of the standards plus additional standards that specify higher data rates. The frequency of a signal impacts it