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Apache in a Wireless World
Originally appearing in WebCompare.Wireless Internet access has the opportunity to serve, literally, every person everywhere. Delivering wireless content to cellular phones and PDAs is similar to but not exactly the same as serving traditional Internet content. Because of these products' limited physical size and communications speeds, new protocols have been developed to package the Web for the wireless world. WAP and WML are the backbones of wireless Web. Placing the Apache Web server into this picture is a natural and easy fit, as Aaron Weiss reports.
Wireless Internet access has the opportunity to serve, literally, every person everywhere. Delivering wireless content to cellular phones and PDAs is similar to but not exactly the same as serving traditional Internet content. Because of these products' limited physical size and communications speeds, new protocols have been developed to package the Web for the wireless world. WAP and WML are the backbones of wireless Web. Placing the Apache Web server into this picture is a natural and easy fit.
While configuring Apache to deliver wireless data is relatively simple, as we will discuss shortly, it is helpful to understand the context of the issues surrounding wireless content delivery.
Land-based Internet communications move data around the world using the TCP/IP protocol. This protocol helps "packets" of data navigate the complex routes across networks, changing paths where necessary to maintain traffic flow across the system. Vendors of wireless communications devices, including such heavyweights as Nokia and Motorola, realized that a data routing system was necessary to push information across wireless networks, which operate with different principles and constraints than physical land lines.
Thus was born the Wireless Application Protocol, or WAP. WAP was designed to push data across the many various types of wireless network topographies in a secure manner, since the wireless space is inherently more vulnerable to eavesdropping than are physical connections. Any operating system can theoretically support WAP. However, the reality is that most devices that will require WAP capabilities will be small in their physical size, like mobile phones and hand-held PDA-style machines.
The consequence of WAP devices' small size is that although WAP as a protocol is perfectly capable of pushing existing data formats such as HTML, these devices are essentially too constrained to properly render documents encoded in these formats, which have been developed with desktop monitors in mind. A companion to WAP was needed then, as well as a defined document format that would render sensibly in the constrained space of small wireless devices.
"And so as wireless begat WAP, WAP in turn begat WML ...", as they might have said in Biblical times had they been writing about content delivery over wireless networks. The Wireless Markup Language, WML, will strike a familiar chord to anyone who has ever worked with the HTML behind most Web pages. In fact, WML is a specific implementation of XML, defining a markup syntax and structure with which users can design pages suitable for a small device.
HTML and WML operate on slightly different underlying metaphors. Whereas HTML is premised on the now-ubiquitous "page" metaphor, WML rests on a "deck of cards" metaphor. Typically, an HTML document represents a single Web page, but a WML document represents a deck within which there can be one or more cards. Navigation within the deck consists primarily of flipping between cards in the deck, either in sequence or via hyperlinks.