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With the omnipresence of XML on client and server computers, it was only a matter of time before it had to show up on alternative devices such as cellular phones and Personal Digital Assistants (PDAs) like Palm and Psion. And so it happened, in the form of the Wireless Application Protocol, WAP.
WAP allows a new generation of mobile phones to browse Web pages in a specialized format called Wireless Markup Language (WML). Telephone service provider all over the world are quickly establishing WAP portals for their customers, and Web portals are launching adaptations of their Web service targetted for the new wireless access methods.
Why is WAP not named MobilePhoneML? Because WAP is much more than just a markup language. It defines:
The application protocol is a layered communicaton protocol that is embedded in each client device. The network side includes a server component implementing the other end of the protocol that is capable of communicating with any WAP client. Often the server component takes on the role of a gateway, routing requests from the user to an application server or Web server.
A WAP application consists of a server application and a client application that the gateway downloads from the application server to the user agent for execution. A standard application environment is needed so that the same client application can be run on different mobile clients. WAP provides such a standard, consisting of a browser and a script interpreter. The script interpreter also implements a set of libraries that allow the application to access certain services of the phone.
Sounds familiar? The WAP architects deliberately picked the successful Web application model and created a parallel wireless universe:
| Internet | Wireless |
|---|---|
| HTML + JavaScript | Wireless Markup Language (WML) + WMLScript |
| HTTP | Wireless Session Protocol (WSP), Wireless Transaction Protocol (WTP) |
| TLS - SSL | Wireless Transport Layer Security (WTLS) |
| TCP/IP, UDP/IP | Wireless Datagram Protocol (WDP), over different bearers such as SMS, CDPD, CSD |
Where the Web has the venerable HTML and JavaScript technologies, WAP has comparable concepts in WML and WMLScript. Session and security protocols have been devised in a similar fashion, and a packet-based transport protocol equivalent to UDP can be overlayed over different existing wireless transport mechanisms (bearers), such as Short Messaging Service (SMS), Cellular Datagram Packet Data (CDPD), or Curcuit Switched Data (CSD).
Next are some WAP specialties.
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Produced by Michael Claßen
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URL: http://www.webreference.com/xml/column12/index.html
Created: May 23, 2000
Revised: May 23, 2000
