rd will not be able to interface directly to an 802.11a access point. The real operational bit rates are much lower than the ideal ones. The gross digit speeds are summarized in Figure 13.38. 802.11a 54 Mbit/s TCP/UDP less 5 GHz band 802.11b 11 Mbit/s 2.4 GHz 802.11g 54 Mbit/s 2.4 Ghz Server Internet From line-of-sight to a number of walls Figure 13.38 Gross digit speeds - the net speed with TCP/IP traffic is considerably less than the gross digit speed Access Network Mobility management Subscriber management Signalling access network Billing/charging Security management 2G/3G core network Functionality within WLAN access network and access to 2G/3G core network functionality provided by solutions based on IETF protocols Figure 13.39 Cooperation between WLAN and 2 G/3G mobile systems WLAN as an Extension to Mobile Systems (ex GPRS and UMTS) For a mobile operator, WLAN is a complementary access technology, especially for city area packet data service offerings. The solution gives broadband mobile public access to the Internet and to corporate intranets. Combined cellular and WLAN could be interesting to business professionals. They already use mobile phones and they usually bring their laptop computers along when they travel. Trouble-free access to the Internet, intranet, e-mail and corporate applications is becoming an everyday necessity. Combined cellular and WLAN allows GPRS and UMTS customers to take advantage of WLANs at indoor environments (hot spots) such as airports and hotels conference areas, and roam between cellular and WLAN networks without interruption. Figure 13.39 gives an idea what UMTS functions and FPs could support WLAN access. Authentication (part of security) and VPN functionality mechanisms are some specific functions that are offered to WLAN. New user segments are expected to pick up WLAN, such as young people using WLAN for interactive gaming and entertainment UMTS operators can provide two access forms to mobile packet data services: one via the wide area UMTS network (WCDMA-based) and th