tailieunhanh - Communication Systems for the Mobile Information Society phần 8

Internet cũng có sẵn mà không có bảo hiểm UTMS tồn tại và cũng đảm bảo kết nối khi đi du lịch ở nước ngoài (chuyển vùng quốc tế). Khi mạng lõi UMTS là một sự tiến hóa đã có GSM và GPRS, một chức năng lập hóa đơn giải pháp trên toàn thế giới đã tồn tại. | Wireless Local Area Network WLAN 245 Internet is also available where no UTMS coverage yet exists and also ensures connectivity when traveling abroad international roaming . As the UMTS core network is an evolution of the already existing GSM and GPRS networks a functioning world-wide billing solution already exists. WLAN on the other hand does not have a standardized billing solution. This is due to the fact that for many scenarios like for home and office use for which the WLAN standard was initially conceived no billing was necessary. For commercial hotspots like in hotels however billing is an essential task. Due to missing standards and the vast number of hotspot operators a number of different billing methods are appearing on the market. These range from scratch cards that can be bought at the hotel s reception desk online credit card payment and billing via the GSM or UMTS. The later billing method can only be used if the WLAN hotspot is operated by the mobile operator of the user. In most cases a user is therefore not able to use the hotspot right away but has to deal with billing first. An open issue for public use of WLAN is the technical realization of lawful interception by the authorities. This contrasts other telecommunication networks including GSM GPRS and UMTS for which most countries have passed laws and standardized methods to allow access by police and other organizations to the data that a user transfers. This process has not yet started for WLAN hotspots and is also not easily achievable due to the current user authentication architecture. With the increasing success of WLANs it is likely that laws will be put into place for this technology as well. This will force many WLAN hotspot operators to redesign their current user authentication and data routing functionality. WLAN has been designed for small coverage areas. This area can be somewhat increased by using several access points to form an ESS. As all access points have to be in the same .