The UP.Link platform, shown in Figure 1-1 below, provides subscribers with secure, wireless access to a wide array of Internet and other network services using data-capable wireless phones or personal digital assistants (PDAs). For the purposes of this documentation, these specially-enabled handheld devices are called UP.Phones.
Using an UP.Phone is much like using a conventional Web browser. The user presses keys to navigate and request URLs. Unlike standard browsers which use the Hypertext Markup Language (HTML) to display information on a computer screen, UP.Phones use the Wireless Markup Language (WML), an open language developed by the Wireless Application Protocol (WAP) Forum1 to accommodate small handheld devices. Like HTML, WML is tag-based and supports text and image presentation, data input, and forms.
The UP.Phone uses the data capabilities of conventional wireless networks to send user requests to the UP.Link Server. The UP.Link Server converts these requests into Hypertext Transport Protocol (HTTP) requests and forwards them over the Internet. When the target service responds, the UP.Link Server relays that information back to the UP.Phone.
The UP.Link Server is the core of the UP.Link platform. Its ability to serve as an HTTP proxy for UP.Phones lets subscribers access any site on the World Wide Web. Some information providers also offer WML services that use WML to take advantage of the UP.Phone interface. These services can also initiate communication by "pushing" information to the UP.Link Server, which, in turn, relays it to an UP.Phone. This process is called notification.
In addition to HTML translation, the UP.Link Server provides a number of other services. It acts as an information gatekeeper by maintaining a database of UP.Phones and their access privileges. It provides optional fax services that let UP.Phone users fax Web site content (including text, Microsoft Word, and Postscript files) to a local fax machine. It also provides configuration parameters that allow administrators to monitor or log transactions.