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Understanding WAP Wireless Applications, Devices, and Services phần 4

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Mặc dù WAP-kích hoạt điện thoại chỉ là trong quá trình được đưa ra, hiện nay có khoảng 200 triệu thuê bao GSM sử dụng các thiết bị không dây. Tìm kiếm ít hơn năm năm tới, dự báo của các nhà sản xuất thiết bị cầm tay lớn dự đoán con số này có thể sẽ tăng lên 700 hoặc 800 triệu, và chúng tôi có lý do tốt để tin rằng phần lớn các thiết bị cầm tay sử dụng sẽ hỗ trợ WAP | Page 73 4.5 WTA services and WTA service providers A WTA service consists of executable content that uses the features provided by the WTA and WAE frameworks. Content building a WTA service is typically stored in the repository and triggered by events in the mobile network using the event-handling mechanism defined in WTA and accessing the mobile device s functionality through WTAI. A WTA service is delivered by a WTA service provider who could be the mobile telephony service provider the operator to which the user subscribes or a content or service provider that is authorized by the mobile telephony service provider to deliver WTA services. A WTA service provider offers enhanced telephony services to a WTA user agent by providing content and services accessible on a WTA server. 4.6 WTA security model and access control When transferred from a WTA server to a client WTA service content is separated from other content by the use of different WDP port numbers on the WAP gateway. A WTA user agent always uses specific WDP ports on the WAP gateway when establishing a WSP session and such a session is the only one allowed to transfer WTA content to a WTA user agent. Content that is not related to WTA services is to be transferred through the WAP gateway using other predefined ports. This mechanism is pictured in Figure 4.3. The security mechanism presently available in WAP provides transport layer security. This security is implemented using WTLS between two WTLS connection endpoints of which a client is one and a WAP gateway or an origin server with built-in gateway functionality is the other. WTLS allows for the WTA user agent to authenticate a WAP gateway and have WTA service content encrypted when transferred between the WAP gateway and the WTA user agent. A WTA user agent uses this authentication to identify specified gateways that are supervised by the mobile telephony service provider and trusted for delivery of WTA services. At the time of writing this chapter .